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kreios 11-17-2017 03:41 PM

[Blog] n-Body Politics
 
https://nbodypolitics.gitlab.io/

Finally starting a blog on the setting I had in mind for some time. I will also include corresponding rules, examples, and thoughts on GURPS rules related to sci-fi.

Starting with the first post:

Quote:

Originally Posted by https://nbodypolitics.gitlab.io/2017/11/17/introduction.html
For quite some time, I have worked on/thought about/written some things down on a setting I have preliminarily called n-Body Politics. Themes and ideas have changed over the last years, but the basics have remained the same - itís supposed to be a fairly hard science-fiction setting concentrating on themes of politics, humans, and space.

For inspiration, look at Transhuman Space, the Expanse, or 2300 AD - this is not Star Warís slow spaceships and fighters. Itís Newtonian movement (Einsteinian movement will probably not be attained), space combat with kinetics and lasers, and most crucially without energy shields.

But itís not supposed to be about war (though the technology and military positions shape arguably do shape the world) - itís about the people living in it. And yes, itís also about conflicts on a state/nation level.

Continue reading...

vicky_molokh 11-18-2017 04:33 AM

Re: [Blog] n-Body Politics
 
/me warily wonders if the politics will be optimistic like THS, or follow the lead of grim darkness of the Expanse . . .

kreios 11-18-2017 07:54 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by vicky_molokh (Post 2136727)
/me warily wonders if the politics will be optimistic like THS, or follow the lead of grim darkness of the Expanse . . .

I'm actually not sure whether the Expanse is that much darker than THS.

No, wait, hear me out!

Spoilers follow, but I'm trying to mark at least those for the later books.

I'd argue that much of the Expanse's less optimistic parts stem from the two factors of essentially only having a bipolar world and weapon yields. Note that I'm only looking at the Protomolecule as a generic catalyst of tension; the same might have been achieved by new technology.

Now, much of the tension comes from the fact that there are essentially only two main factions (Earth and Mars) plus the Third-World-equivalent (the Belt). This means that your conflicts are immediately much bigger, and escalation (coupled with the high weapon yields) much more dangerous.

However, I'd argue that THS, were it a bipolar world, could easily see something like that. The Pacific War can be compared to any of the Earth/Mars conflicts in the Expanse, except it actually went hot even on Earth. It just wasn't as destructive because the two factions didn't cover half a globe. Or look at the Andes War.

We also, in THS, tend to concentrate on the fifth-wave nations and on space (which has to have a high TL). The Expanse, on the other hand, looks at the proverbial underbelly of the system. What do you know about Earth? That there are 30 billion people who, according to Martian propaganda, consume free drugs and get a basic income. That suggests an acceptably high planetary income, but we almost never visit those places.

Spoiler for Nemesis Games
Spoiler:  


In summary, I'd actually say that the differences come more from a concentration on the poorer areas, only two main powers, and a higher "vulnerability" of the whole setting and situation - a necessity if you want to have those high-stakes stories. THS is still more optimistic, though.

But don't worry, I plan to be inspired much more by THS.

evileeyore 11-18-2017 12:40 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by vicky_molokh (Post 2136727)
... grim darkness of the Expanse . . .

In the grim darkness of the Expanse there is only Protomolecule!

kreios 11-22-2017 12:47 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by https://nbodypolitics.gitlab.io/2017/11/22/ftl_travel.html
Having done the introduction, the next logical step is to look at how the setting differs from today. And the main difference is - quite obviously - space. In itself, we can look at space technology in three different perspectives: Faster-than-light travel, STL travel and interface (or surface-to-orbit) travel. Weíll start with the FTL travel.

One might argue that one of the main setting decisions is which FTL drive to use. We need an FTL drive to get to other planets (the Space in our Space Opera) - and any restriction and attribute of the FTL drive shapes our setting.

Continue reading...

Emerald Cat 11-22-2017 05:44 PM

Re: [Blog] n-Body Politics
 
--Thoughts on FTL system--

Overall, your hyperdrive looks good. I'm confused, though. What is the range on your FTL drive? Or have you not come up with a specific number yet?

Note that your FTL design hasn't eliminated the potential for c-fractional (i.e. relativistic) projectiles. If you can drop out of hyperspace around asteroids, what is stopping you from dropping out at an asteroid in interstellar space? That would give you enough range to reach c-fractional velocity if you have a reactionless drive. If you're going to include reactionless STL drives, preventing this kind of abuse requires the FTL drive to be limited to the main part of a system or have sensors capable of detecting ships traveling at FTL at interstellar ranges.

Having the exclusion zone scale with mass seems more plausible than it scaling with diameter. That is a little more cumbersome than just using the diameter of the object. But on par with the math you would need to use the reaction drives from Spaceships.

However, I find it hard to believe that the arrival zone has a hard boundary. I'd allow daring captains to jump in closer. But I can't figure out an astrogation penalty scheme that is light enough to make this plausible without making it so easy that everyone would risk it to cut right to the recharge zone. So never mind.

Speaking of which, what is being recharged at these pit stops?

--Other Thoughts--

Does FTL communication exist in this setting? Or is communication limited to ship speeds?

kreios 11-23-2017 11:29 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Emerald Cat (Post 2138015)
--Thoughts on FTL system--

Overall, your hyperdrive looks good. I'm confused, though. What is the range on your FTL drive? Or have you not come up with a specific number yet?

Both, actually: The FTL drive has a certain range defined (1/5th of the distance between habitable planets, and about one jump per unimportant system), but not in LY yet. If we take the average density of stars near Earth, then the range is about 6-8 LY.

Quote:

Note that your FTL design hasn't eliminated the potential for c-fractional (i.e. relativistic) projectiles. If you can drop out of hyperspace around asteroids, what is stopping you from dropping out at an asteroid in interstellar space? That would give you enough range to reach c-fractional velocity if you have a reactionless drive. If you're going to include reactionless STL drives, preventing this kind of abuse requires the FTL drive to be limited to the main part of a system or have sensors capable of detecting ships traveling at FTL at interstellar ranges.
Very good point. It does at least make acceleration-FTL-undetected annihilation impossible. But, spoilers, I'll not take reactionless drives.

Quote:

However, I find it hard to believe that the arrival zone has a hard boundary. I'd allow daring captains to jump in closer. But I can't figure out an astrogation penalty scheme that is light enough to make this plausible without making it so easy that everyone would risk it to cut right to the recharge zone. So never mind.
Actually, this is an interesting idea. I had an idea about the recharge limit as a more flexible boundary (which roughly scales like a sigmoid function, meaning you don't have to get closer to the main star if you're willing to wait for a few weeks). I'll keep it in mind for a revision.

Quote:

Speaking of which, what is being recharged at these pit stops?
Space Magic. Maybe the FTL core is starting to get decoherent during jumps and needs gravity to regenerate. I'll have to think about an in-universe reason.

Quote:

--Other Thoughts--

Does FTL communication exist in this setting? Or is communication limited to ship speeds?
I don't think it will, and neither will FTL sensors. However, I'll decide in the future.

Also, thank you for the interest!

ericthered 11-24-2017 12:05 PM

Re: [Blog] n-Body Politics
 
They start at rest with regards to the object? Ok, that took guts to go for. It also means that if your STL light drives fails, you face certain death after a FTL jump.

5 kps is a huge delta-V cost, particularly if you make it apply both ways. with 10 kps I can get into orbit from earth's surface. And I can't just use an efficient Ion drive, because I'll slam into the earth first. So it looks like I'm going to have to spend large parts of my ship either storing fuel or massing three rocket engines to get the acceleration I need. Its not as bad as planetary take-off, fortunately, because falling is an option, and because you don't need to accelerate quite as fast, but it still places restricting demands on the drives.

So I wanted to know how different sizes of planet act with these rules, and what minimal spacecraft engines look like. And you made me spend an hour doing math. Hopefully some of it will be useful to you:

if you don't use engines after appearing around earth, you have a little less than 8 hours before you impact. using 1.11 * (R^3/(GM))^.5 gives the time to the center of the body. I figured the actual numbers, but those equations are nasty, and this gives pretty good results.

Resting time to impact simplifies down to about 35 * (GM)^.25 if you use .1 newtons instead of .01G

Engines need to be .015 G's or greater in order to make orbital velocity before the powered crash time is up. This is constant regardless of the body you are orbiting. the actual minimum is something else, but it lower, depends on the mass and radius of the orbiting body, and this is probably a good rule of thumb. It's also interesting, because a lot of rocket engines play just above or just below this values.

The KPS for the resting orbit of a body is (GM)^.25

the resting orbit for a body is (GM)^.5

* I am sorry for liberally mixing earth gravity with the gravitational constant, both represented by G. If the G has an M next to it, its the gravitational constant.

On minimally viable objects, all the planets have a recharge zone, the Galileans and Titan have recharge zones, but Pluto and Ceres do not, reinforcing the categorization of them as dwarf planets. Earth's moon does have a recharge zone, and in fact bodes like it take less fuel to use as stopping places. The cheapest place to stop in the solar system is Europa, but the next is earth's moon, both being about of third of what you'd spend to land on earth. There are probably some kuiper belt objects that can be used as rechargers, but we haven't found any in the solar system, which means they may very well be secrets well guarded by militaries, guilds, and smugglers. Or valuable waypoints through gaps in a network.

You CAN use a star directly, but you'll want really big fuel tanks to pull that off. A minimal red dwarf requires 50 kps to stabilize, and twice that if you ever want to leave. The sun requires 107 kps to stabilize. I think the minimum vessel I'd try jumping to a star would have 3 Advanced pulsed fusion drives, 2 fusion engines, and 11 tanks of fuel at TL9. The remaining fifth of the ship is probably shielding, control, life support, and living quarters for the nuts trying this out. And two weeks worth of food.

kreios 11-26-2017 06:39 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by ericthered (Post 2138300)
They start at rest with regards to the object? Ok, that took guts to go for. It also means that if your STL light drives fails, you face certain death after a FTL jump.

It's actually not that different from any other method: If your main drive fails, you'll either crash into something or will be on a month-long journey for which your supplies probably won't hold. (Excepting things like a free return trajectory).

Quote:

5 kps is a huge delta-V cost, particularly if you make it apply both ways. with 10 kps I can get into orbit from earth's surface. And I can't just use an efficient Ion drive, because I'll slam into the earth first. So it looks like I'm going to have to spend large parts of my ship either storing fuel or massing three rocket engines to get the acceleration I need. Its not as bad as planetary take-off, fortunately, because falling is an option, and because you don't need to accelerate quite as fast, but it still places restricting demands on the drives.
Agreed, and this is something we'll see in the next post.

Quote:

if you don't use engines after appearing around earth, you have a little less than 8 hours before you impact. using 1.11 * (R^3/(GM))^.5 gives the time to the center of the body. I figured the actual numbers, but those equations are nasty, and this gives pretty good results.

Resting time to impact simplifies down to about 35 * (GM)^.25 if you use .1 newtons instead of .01G

Engines need to be .015 G's or greater in order to make orbital velocity before the powered crash time is up. This is constant regardless of the body you are orbiting. the actual minimum is something else, but it lower, depends on the mass and radius of the orbiting body, and this is probably a good rule of thumb. It's also interesting, because a lot of rocket engines play just above or just below this values.
Quite interesting, and I didn't actually compute that myself - I had just assumed that a sufficiently strong engine (which I've already defined) would be available. I'll definitely have to spend another post later on on a few more options and math.

Quote:

On minimally viable objects, all the planets have a recharge zone, the Galileans and Titan have recharge zones, but Pluto and Ceres do not, reinforcing the categorization of them as dwarf planets. Earth's moon does have a recharge zone, and in fact bodes like it take less fuel to use as stopping places. The cheapest place to stop in the solar system is Europa, but the next is earth's moon, both being about of third of what you'd spend to land on earth. There are probably some kuiper belt objects that can be used as rechargers, but we haven't found any in the solar system, which means they may very well be secrets well guarded by militaries, guilds, and smugglers. Or valuable waypoints through gaps in a network.
Also very interesting. My assumption is that the range is sufficiently high that there's almost always going to be a few stars in range, and that brown dwarfs would be too inefficient to stop at for a commercial route.

ericthered 11-27-2017 09:15 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by ericthered (Post 2138300)
You CAN use a star directly, but you'll want really big fuel tanks to pull that off. A minimal red dwarf requires 50 kps to stabilize, and twice that if you ever want to leave. The sun requires 107 kps to stabilize. I think the minimum vessel I'd try jumping to a star would have 3 Advanced pulsed fusion drives, 2 fusion engines, and 11 tanks of fuel at TL9. The remaining fifth of the ship is probably shielding, control, life support, and living quarters for the nuts trying this out. And two weeks worth of food.

I just realized what this ship is: its a surveyor. Detecting planets around stars from light years away is something of a hit and miss proposition that takes big equipment and a ton of analysis. If you're in the system, it becomes much easier. So you send a ship to the next star you need mapped, it maps everything, and you can extend your charts with only a week or two of effort. You need to stay for about that amount of time to calculate the orbits of the moons in sol system anyway, unless you have really good gear (which is heavy, and you probably have to stay that long anyways).

Unless there is a way to fire the FTL twice in quick succession. Then that might become the best way to do surveys.

Quote:

Originally Posted by kreios (Post 2138657)
Also very interesting. My assumption is that the range is sufficiently high that there's almost always going to be a few stars in range, and that brown dwarfs would be too inefficient to stop at for a commercial route.

Brown dwarfs are a pretty expensive option, yeah. Its actually shorter to use the moon 10 times than to use jupiter once. I wasn't thinking of brown dwarves. I was thinking of some Icy body like Pluto or Eris orbiting a star at long distance. Eris is within 20% gravity of letting you recharge your drive. Such a body is going to be hard to find and cheap to travel to: great for smugglers, pirates, and military forces.

kreios 11-29-2017 01:13 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by https://nbodypolitics.gitlab.io/2017/11/29/interface_propulsion.html
Last time, we talked about FTL travel. However, to be able to FTL-travel, we still need to leave that pesky gravity well behind - and at roughly 9.4km/s, itís a doozy. Just looking at todayís rockets, mass fractions and propellant densities make multi-stage rockets necessary. But how does it look like in the future?

Continue reading...

Humabout 11-29-2017 04:41 PM

Re: [Blog] n-Body Politics
 
A note on your lift-off requirements and acceleration: as you decrease acceleration, the delta-v needed to attain orbit increases, thanks to gravity drag. Thus, blasting off at 3g takes less delta-v worth of fuel than doing it at 1.1g. To that end, if you correct for this, you'll find your assessment of boosters is off. You'll also (correctly) find that SSTO is just a dream for hlox, kerolox, and metholox engines.

kreios 12-03-2017 01:00 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Humabout (Post 2139504)
A note on your lift-off requirements and acceleration: as you decrease acceleration, the delta-v needed to attain orbit increases, thanks to gravity drag. Thus, blasting off at 3g takes less delta-v worth of fuel than doing it at 1.1g. To that end, if you correct for this, you'll find your assessment of boosters is off. You'll also (correctly) find that SSTO is just a dream for hlox, kerolox, and metholox engines.

A good point. It's just a rough estimate, but the conclusion stays valid in my opinion: Forget launching anything with conventional rockets if you want to remain economical.

Speaking of which: Next post!



Quote:

Originally Posted by Space Propulsion
Now weíre moving to the interesting topic of space propulsion, and which one to use. Since GURPS Spaceships offers a large number of them, Iím only going to look at the best ones - some, like ion drives or chemical rockets, are simply going to lack in either thrust or efficiency to be useful.

Continue reading...

Humabout 12-04-2017 10:58 AM

Re: [Blog] n-Body Politics
 
Again, an interesting analysis, but a few things to consider when discussing torches. While ISP is a measure of efficiency, it should be noted that rockets generally cannot be throttled down terribly far (iirc, the Merlin has the widest range at present and can be reduced to 30% max thrust). This means that a torch will not only provide constant acceleration (meaning high-dv transfers), but they also have higher thrusts (meaning even more dv consumption). The end result is that torches eat far more fuel than non-torches, but they do get you there faster.

Why do we care? Economics. It actualy turns out that, at TL 11 (because that's the TL I did the analysis at a while back), the most economical engine for anything outside of cislunar space is a fusion torch, with advanced nuclear pulse drive a close runner up (im doing this from memory; those might be reversed. I'll see if i still have the spreadsheet for this). Inside cislunar space, an ion drive is cheapest. And beyond Neptune, you have to use a pion drive and it's going to wreck your budget.

This analysis assumed single stage craft. Beyond Neptune might be achieved more cheaply with staged fusion engines/anpu.

If this doesn't square with the FTL drive requirements, ships may need a set of auxiliary high-G engines, or the FTL drive might need tweaking to "just work".

As for combat, again, a set of high-g engines might be useful for maneuvering. This does address two issues at once.

Also, recall that all of the above engines, excepting the ion drive, are probably too hazardous for populated space. This would indicate the presence of tugs that tow inyerplanetary ships into and out of port, so they can fire their engines safely. These tugs would likely use either high-g HEdM rockets or ion engines (again, cost).

The alternative to tugs are ion-engine-shuttles that transfer passengers and cargo from inhabited space to parking orbits further out where its safe to fire up a the kind of radioactive nightmare that is a ANPU drive or fusion drive.

ericthered 12-04-2017 11:36 AM

Re: [Blog] n-Body Politics
 
Quote:

Why do we care? Economics. It actually turns out that, at TL 11 (because that's the TL I did the analysis at a while back), the most economical engine for anything outside of cislunar space is a fusion torch, with advanced nuclear pulse drive a close runner up (im doing this from memory; those might be reversed. I'll see if i still have the spreadsheet for this). Inside cislunar space, an ion drive is cheapest. And beyond Neptune, you have to use a pion drive and it's going to wreck your budget.
I've got my spreadsheet handy: The best ISP is the advanced Fusion pulse drive. Its got better ISP than the torch at all TL's. The non-advanced fusion pulse drive is slightly under the torch. Of course, the torch has 10 times the power of the non-advanced and 100 times the power of the advanced drives. Freighters probably use the advanced Fusion Pulse drives.

Quote:

Originally Posted by Humabout (Post 2140537)
Again, an interesting analysis, but a few things to consider when discussing torches. While ISP is a measure of efficiency, it should be noted that rockets generally cannot be throttled down terribly far (iirc, the Merlin has the widest range at present and can be reduced to 30% max thrust). This means that a torch will not only provide constant acceleration (meaning high-dv transfers), but they also have higher thrusts (meaning even more dv consumption). The end result is that torches eat far more fuel than non-torches, but they do get you there faster.

I don't think the math there follows. You can't burn a rocket at 10% of total thrust, but you can burn a rocket for 10% as long, assuming its not a solid booster and you have reasonable tolerances.

kreios 12-04-2017 01:07 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Humabout (Post 2140537)
Again, an interesting analysis, but a few things to consider when discussing torches. While ISP is a measure of efficiency, it should be noted that rockets generally cannot be throttled down terribly far (iirc, the Merlin has the widest range at present and can be reduced to 30% max thrust). This means that a torch will not only provide constant acceleration (meaning high-dv transfers), but they also have higher thrusts (meaning even more dv consumption). The end result is that torches eat far more fuel than non-torches, but they do get you there faster.

As ericthered said, this is only an issue if we're assuming non-restartable engines. Which often happens in real-life - most rocket engines aren't restartable, and something like the Vinci engine with three or four ignitions is noted to increase Ariane 5's flexibility by quite a bit.

However, if our engine is restartable, a high-thrust engine is superior to a same-ISP low-thrust engine, since you can simply spend your dV over a shorter period of time. This also allows you to follow several trajectories which you otherwise couldn't follow (Hohmann orbits generally assume instant acceleration) and greatly simplify your orbital math.

Quote:

Why do we care? Economics. It actualy turns out that, at TL 11 (because that's the TL I did the analysis at a while back), the most economical engine for anything outside of cislunar space is a fusion torch, with advanced nuclear pulse drive a close runner up (im doing this from memory; those might be reversed. I'll see if i still have the spreadsheet for this). Inside cislunar space, an ion drive is cheapest. And beyond Neptune, you have to use a pion drive and it's going to wreck your budget.
Not unlikely. While the fusion pellets cost 25x as much as hydrogen, they also provide almost 8x as much dV, which means you should be cheaper at about... Interestingly, my back-of-the-envelope calculations give me 3000km/s dV needed (assuming no cost due to increased volume and mass), which is probably quite wrong.


Quote:

Also, recall that all of the above engines, excepting the ion drive, are probably too hazardous for populated space. This would indicate the presence of tugs that tow inyerplanetary ships into and out of port, so they can fire their engines safely. These tugs would likely use either high-g HEdM rockets or ion engines (again, cost).

The alternative to tugs are ion-engine-shuttles that transfer passengers and cargo from inhabited space to parking orbits further out where its safe to fire up a the kind of radioactive nightmare that is a ANPU drive or fusion drive.
The way it seems right now, one of the big lies in the setting will be a non-radiation-spewing fusion torch. I need my cheap spacelift.

Quote:

I've got my spreadsheet handy: The best ISP is the advanced Fusion pulse drive. Its got better ISP than the torch at all TL's. The non-advanced fusion pulse drive is slightly under the torch. Of course, the torch has 10 times the power of the non-advanced and 100 times the power of the advanced drives. Freighters probably use the advanced Fusion Pulse drives.
Most importantly, though, the fusion torch's propellant is also only $2000 (or $20 with water) per ton, compared to the $50,000 per ton for the pulse drives. That will probably make it more economical for almost all trade - if you can assume waystations, it will be more economical.

ericthered 12-04-2017 01:27 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by kreios (Post 2140573)
Most importantly, though, the fusion torch's propellant is also only $2000 (or $20 with water) per ton, compared to the $50,000 per ton for the pulse drives. That will probably make it more economical for almost all trade - if you can assume waystations, it will be more economical.

I missed that. For some reason I thought you'd be using raw hydrogen to fuel the pulse drives. That certainly makes the torches cheaper than the pulse drives.

It still leaves fusion rockets outperforming the torches, but its a narrower margin (x4 instead of x7). Actually, you probably won't strain credulity any more than the torch already does if you let one engine switch freely between rocket and Torch mode. Though that may just complicate your math more.

Are you trying eliminate space only craft as an element?

kreios 12-04-2017 02:27 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by ericthered (Post 2140581)
Are you trying eliminate space only craft as an element?

On the contrary - I find it strains my disbelief to see gigantic spacecraft (without superscience, of course) land. For me, it'll probably be shuttles and drop pods. And elevators, of course.

Humabout 12-04-2017 09:11 PM

Re: [Blog] n-Body Politics
 
The issue, Eric, is that constant acceleration transfers naturally achieve higher delta-vs than impulse transfers. And the higher your acceleration, the more delta-v such a transfer takes. So if you have a 0.1g acceleration drive running nonstop, it eats more delta-v than a 0.01g accel drive between The Same Orbits. Thus, lower accel drives tend to use less fuel, regardless of isp.

Kreios, I never said anything about restartability. I addressed throttle-ability. Modern rocket engines can't operate below about 30% max thrust. They can turn off and fire back up. Heck, JPL is looking at using the auxiliary thruster on Voyager 1 for attitude control after its been mothballed for 40 years. But they can't run it at 10% thrust.

The reason that matters is that you can't dial back a 1g drive down to 0.005g to get a lower delta-v transfer that doesnt take over a decade to get to Saturn (Hohhman). This is inherent to the drives and presents an unintuitive challenge when analyzing costs.

Ultimately, you want to cost transfers by ($/ton)(ton/dv) or ($/dv). Thus, the more dv, the more money, and then you can balance transit time (crew wages, maintenance costs, etc.) against the cost of fuel to get a ballpark transit time and cost per transit. Spreadsheets are your friend here.

kreios 12-05-2017 12:43 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Humabout (Post 2140664)
The issue, Eric, is that constant acceleration transfers naturally achieve higher delta-vs than impulse transfers. And the higher your acceleration, the more delta-v such a transfer takes. So if you have a 0.1g acceleration drive running nonstop, it eats more delta-v than a 0.01g accel drive between The Same Orbits. Thus, lower accel drives tend to use less fuel, regardless of isp.

Actually, this is wrong. The most efficient transfer is (depending on the ratio between the two orbits) is either a Hohmann or a bi-elliptic transfer. Both assume instant velocity changes, meaning you can never actually achieve them. However, the higher your acceleration, the closer you can get (and therefore need less dV). Assuming you're able to restart engines (bringing us back to that topic, but which means you can actually to those required two burns), a high-thrust engine is always more efficient than a low-thrust one to change orbits.

At the extreme end, we can look at the real-life example of the SMART-1 mission, which expended ~3.9km/s dV from a geostationary transfer orbit to a low lunar orbit. However, an optimal trajectory (such as produced by a high-thrust system) would only need ~1.5km/s dV for such a transfer. Of course, the ion engine was far more efficient in terms of propulsion (since its Isp is more than four times a chemical rocket's) - but if they would've had a high-thrust system with those numbers available, they would've used it.

Humabout 12-05-2017 01:55 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by kreios (Post 2140765)
Actually, this is wrong. The most efficient transfer is (depending on the ratio between the two orbits) is either a Hohmann or a bi-elliptic transfer. Both assume instant velocity changes, meaning you can never actually achieve them. However, the higher your acceleration, the closer you can get (and therefore need less dV). Assuming you're able to restart engines (bringing us back to that topic, but which means you can actually to those required two burns), a high-thrust engine is always more efficient than a low-thrust one to change orbits.

At the extreme end, we can look at the real-life example of the SMART-1 mission, which expended ~3.9km/s dV from a geostationary transfer orbit to a low lunar orbit. However, an optimal trajectory (such as produced by a high-thrust system) would only need ~1.5km/s dV for such a transfer. Of course, the ion engine was far more efficient in terms of propulsion (since its Isp is more than four times a chemical rocket's) - but if they would've had a high-thrust system with those numbers available, they would've used it.

Actually, this is correct in the context in which I was speaking.

1) Eric and I are addressing cost efficiency, not dv efficiency - which itself doesn't necessarily translate into mass efficiency or cost efficiency. And what will ultimately determine which engines get used in some hypothetical futurist setting is the combination of cost and demand.

2) Hohhman, bi-elliptic (that ration is 11:1, btw), and other high-thrust transfers are the least time-efficient transfers available. This makes them highly undesirable for most applications of space flight, both because no one wants to sit on a spaceship for a decade while they drift toward Saturn and because no company wants to pay a crew a decade of wages to drift toward Saturn once.

3) The fastest transfers available use constant thrust to attain high velocities over the course of the transfer. This necessarily increases dv, which in turn, increases the fuel costs. It, however, saves time, and thus allows more trips (meaning more revenue) and fewer paid crew hours (meaning lower expenses). This is desirable when maximizing profit, and thus, monetary efficiency.

4) When dealing with brachistochrone transfers, the higher the craft's acceleration, the higher the maximum velocity attained, and thus the more dv required to execute it. Thus, a fusion torch can pull 0.5G, it would need approximately 800 mps - meaning 13 fuel tank systems - to transfer from Earth to Mars, and you would have to refuel there. But, even a regular fusion rocket could pull 0.005G, need only 100 mps and make the trip there and back again on less than 2 fuel tank systems. They use the same type of fuel, so it's pretty plain to see that a fusion rocket is more cost efficient than a fusion torch. Or in other words, the lower-thrust drive is more cost efficient than the higher-thrust drive.

5) High-thrust rocket engines have existed since 1926. They had a high-thrust system available for the SMART-1 mission and chose to use a high-efficiency, low-thrust ion engine instead. It had a higher dv because it went faster, but it had a far lower fuel-mass percentage (3.33%) specifically because the ion engine was more efficient.

kreios 12-05-2017 02:29 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Humabout (Post 2140780)
3) The fastest transfers available use constant thrust to attain high velocities over the course of the transfer. This necessarily increases dv, which in turn, increases the fuel costs. It, however, saves time, and thus allows more trips (meaning more revenue) and fewer paid crew hours (meaning lower expenses). This is desirable when maximizing profit, and thus, monetary efficiency.

4) When dealing with brachistochrone transfers, the higher the craft's acceleration, the higher the maximum velocity attained, and thus the more dv required to execute it. Thus, a fusion torch can pull 0.5G, it would need approximately 800 mps - meaning 13 fuel tank systems - to transfer from Earth to Mars, and you would have to refuel there. But, even a regular fusion rocket could pull 0.005G, need only 100 mps and make the trip there and back again on less than 2 fuel tank systems. They use the same type of fuel, so it's pretty plain to see that a fusion rocket is more cost efficient than a fusion torch. Or in other words, the lower-thrust drive is more cost efficient than the higher-thrust drive.

Ah. I believe this is where we miscommunicated. And, I should add, I actually believe one of your assumptions don't necessarily hold. But for this, let's look at some numbers.

Specifically, ignoring orbits, your goal is to move to a target at 1 AU. Your available engines are a fusion rocket (0.005G, v_exh 10290km/s or 350mps/525km/s dV per tank) or a hydrogen-fuelled fusion torch (0.5G, v_exh 1323km/s or 45mps/67.5km/s dV per tank). I'm also ignoring acceleration changes due to fuel expenditure.

A brachistochrone transfer with the fusion rocket will take you just over 40 days (20 each spent accelerating and decelerating). In total, you spend about 175km/s dV for this (1/3rd of a tank).

A brachistochrone transfer with the fusion torch will take 4 days, spending an astronomical ~1750km/s of dV (surprisingly, that's just ~15 tanks). I believe that's where your numbers came from.

However, you can also use the fusion torch to accelerate to 87.5km/s, coast for some time, then decelerate. Total dV spent is 175km/s too (~2.5 tanks), but you spend slightly less than five hours each to accelerate/decelerate, and ten days coasting. In total, you spent the same dV, but cut your transfer time by 75%. In fact, you can achieve the same transit time as with the fusion rocket's constant acceleration by spending just 45km/s dV (2/3rds of a tank)!


Quote:

5) High-thrust rocket engines have existed since 1926. They had a high-thrust system available for the SMART-1 mission and chose to use a high-efficiency, low-thrust ion engine instead. It had a higher dv because it went faster, but it had a far lower fuel-mass percentage (3.33%) specifically because the ion engine was more efficient.
By "these numbers", I meant a high-thrust engine with similar dV. I should have made that clearer; apologies.

kreios 12-11-2017 11:06 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by The economics of interface travel
We now know what our space and interface propulsion looks like: Fusion torches, probably using water. What remains to be defined is the impact our technology has on the economy - how much does it cost to transport cargo or passengers?

Continue reading...

kreios 12-21-2017 08:32 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by The economics of interstellar travel
Getting everything into orbit is only the first part in a long journey. For the next one, weíll have to look at interstellar transport.

Continue reading...

johndallman 12-21-2017 08:41 AM

Re: [Blog] n-Body Politics
 
Quote:

To simplify math, all FTL jumps will deposit the spacecraft into a stable orbit.
It seems better to change that to FTL jumps being able to deposit the spacecraft into a stable orbit, if the dynamics of the target are known with sufficient accuracy. Otherwise you get weirdness with exploratory jumps, arguments over the definition of "stable orbit" and so on.

vicky_molokh 12-21-2017 10:17 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by ericthered (Post 2144530)
Huh, some interesting decisions here:

I'm not sure why you're using a fusion torch instead of a fusion rocket. the rocket has 4x the delta-v. Do you need the speed?

I'm surprised to find out that using water is cheaper than hydrogen, but the math holds up. Even counting transport costs, water is half the dv for 1/50th of the price, and you only decrease cargo space by 25%, so it makes sense. And you probably don't even need pure water: melted ice from an icy moon like Europa will work.

I'm sad to see you drop the FTL "emerging at rest" mechanism. I was having a lot of fun with it.

A freighter really shouldn't have 15% of its mass dedicated to armor, but spaceships always buts it in, so I can see not rocking the boat.

This has been branched off into a separate thread for the cargo/armour discussion.

kreios 12-21-2017 02:53 PM

Re: [Blog] n-Body Politics
 
I'll answer to the relevant points here.

Quote:

Originally Posted by ericthered (Post 2144530)
I'm not sure why you're using a fusion torch instead of a fusion rocket. the rocket has 4x the delta-v. Do you need the speed?

The acceleration, yes. If you only look at the departure burn, the Fusion Rocket needs more than eight hours thrust to produce the necessary dV (which means even more time spent on waiting for periapsis). The torch needs five minutes of thrust.

Quote:

I'm surprised to find out that using water is cheaper than hydrogen, but the math holds up. Even counting transport costs, water is half the dv for 1/50th of the price, and you only decrease cargo space by 25%, so it makes sense. And you probably don't even need pure water: melted ice from an icy moon like Europa will work.
So was I, but - assuming waystations - hydrogen is far too expensive. If I remember correctly, there's a break-even point somewhere between five and ten jumps, so maybe for exploration craft - but on the other hand, they'd have to deal with the hassle of cryogenic hydrogen.

Quote:

I'm sad to see you drop the FTL "emerging at rest" mechanism. I was having a lot of fun with it.
Hm... maybe I should spend a post looking over that mechanism and computing the dV. It might be worth keeping.

ericthered 12-21-2017 04:08 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by kreios (Post 2144629)
The acceleration, yes. If you only look at the departure burn, the Fusion Rocket needs more than eight hours thrust to produce the necessary dV (which means even more time spent on waiting for periapsis). The torch needs five minutes of thrust.

hah, every time I did the math I was assuming three engines: that's how many you need to achieve orbit in 8 hours.

Of course now when I look at costs I realize that engines are among the most expensive things in the book, and two systems, the engine and the stardrive, cost around 70% of the ship already.

Quote:

Hm... maybe I should spend a post looking over that mechanism and computing the dV. It might be worth keeping.
I've done some work. The amount of dv for a given orbit scales with the fourth root of mass and the square root of gravitational influence.

The equations got really complex and than all cancelled out. It was stunning. dv where a planet's influence is g and the mass is M is

dv = (GM)^.25 * g^.5 * .001

Where G is the gravitational constant.

doctorevilbrain 12-21-2017 05:09 PM

Re: [Blog] n-Body Politics
 
When I clicked on the continue reading link, it said "significant costs of surging". What's surging?

kreios 12-22-2017 07:30 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by ericthered (Post 2144651)
Of course now when I look at costs I realize that engines are among the most expensive things in the book, and two systems, the engine and the stardrive, cost around 70% of the ship already.

Extremely so. If you look at the Cargolifter from last post, which costs $8.75M, you'll note that I had designed a ram-rocket variant. Only exchanging the engines means increasing the cost from $8.75M to $60M. Hugely expensive.



Quote:

I've done some work. The amount of dv for a given orbit scales with the fourth root of mass and the square root of gravitational influence.

The equations got really complex and than all cancelled out. It was stunning. dv where a planet's influence is g and the mass is M is

dv = (GM)^.25 * g^.5 * .001

Where G is the gravitational constant.
That really is nice. (I tried reconstructing that formula; I'll probably have to repeat it and expand it in a blog entry, since I got other numbers). One of the issues, of course, is that the orbital math becomes more complicated when considering faster transfer burns.


Quote:

Originally Posted by doctorevilbrain (Post 2144665)
When I clicked on the continue reading link, it said "significant costs of surging". What's surging?

I have updated this passage to "[...] and the arguably significant costs of either coordinating massive numbers of shuttle flights (surging) or in-orbit storage of cargo. Remember - you only have eight hours to load and unload your whole cargo, every hour you waste costs you more than ten thousand dollars."
This hopefully makes it clearer.

thrash 12-22-2017 09:42 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by kreios (Post 2144629)
The acceleration, yes. If you only look at the departure burn, the Fusion Rocket needs more than eight hours thrust to produce the necessary dV (which means even more time spent on waiting for periapsis). The torch needs five minutes of thrust.

I ran into this issue with my own setting, which seems fairly similar to yours. My solution was to create a variant fusion torch with 0.2g per system and 1.5 mps delta-V per tank of water. This is the same basic performance as the fusion rocket (acceleration * ISP = a constant, in this case 0.3 at TL10, vs. 7.5 for the torch as written). It's still limited superscience, due to the temperatures involved, but makes for a more interesting set of tradeoffs.

kreios 12-30-2017 03:06 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Shipping Cargo and Passengers
We now know the cost - but what kind of cargo are we transporting? And how does a passengerís life look like?

Continue reading...

As the last post of the year, a look at the cargo being transported, and how much passengers will pay. Did you know that a freight load of gems can buy you over a hundred freighters?

ericthered 01-02-2018 12:56 PM

Re: [Blog] n-Body Politics
 
You should probably include one level below economy class, that uses bunkrooms instead of shared cabins. I'd keep the establishment and attendant rates the same as for economy class. You can about halve the price for such a class yet again.

I'm under no illusions as to how unpleasant this is. You have no privacy at all from your three bunkmates, and precious little from all the other bunk-rooms nearby, as you will have thin walls and shared joint bathrooms. the Opportunity to cook will be minimal. There will be very little space to walk around or exercise: you'll essentially be confined to your bunk.

And yet people have tolerated such conditions for time immemorial. Much of the US population had their ancestors cross in similar circumstances. This pattern has been used for barracks, and the conditions may be similar or even superior to a ship full of refuges fleeing their country.

I thought that such options should probably be mentioned.

kreios 01-02-2018 03:40 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by ericthered (Post 2147088)
You should probably include one level below economy class, that uses bunkrooms instead of shared cabins. I'd keep the establishment and attendant rates the same as for economy class. You can about halve the price for such a class yet again.

Definitely. That's why I wrote up a bunkroom-based class... except I apparently never added it to the blog. In fact, my first reaction to your post was "But didn't I add this?". I have gone back and edited it in.

Quote:

I'm under no illusions as to how unpleasant this is. You have no privacy at all from your three bunkmates, and precious little from all the other bunk-rooms nearby, as you will have thin walls and shared joint bathrooms. the Opportunity to cook will be minimal. There will be very little space to walk around or exercise: you'll essentially be confined to your bunk.
Yep. Slum-Class passengers have it really hard. I've included a quote from Babylon's Ashes on accommodations like that. Not sure I believe the whole prison-like features (thugs, beatings, blackmail), but it fits well with their storyline.

Quote:

And yet people have tolerated such conditions for time immemorial. Much of the US population had their ancestors cross in similar circumstances. This pattern has been used for barracks, and the conditions may be similar or even superior to a ship full of refuges fleeing their country.
I'll come to colonization later on (probably quite a bit later, since I'm going to stay in space for a while longer - FTL travel revisited up next, followed by space combat).

ericthered 01-03-2018 09:36 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by kreios (Post 2147135)
Definitely. That's why I wrote up a bunkroom-based class... except I apparently never added it to the blog. In fact, my first reaction to your post was "But didn't I add this?". I have gone back and edited it in.

Such things happen.


Quote:

Yep. Slum-Class passengers have it really hard. I've included a quote from Babylon's Ashes on accommodations like that. Not sure I believe the whole prison-like features (thugs, beatings, blackmail), but it fits well with their storyline.
I suspect slum-class situations are especially dependent on the circumstance and origin of the travelers. And the circumstance and origin of travelers is especially varied for slum-class ships. There is a great opportunity for unregulated and unpoliced behavior between strangers shoved into close proximity. And there is a good possibility that crime was common among them without the extra opportunity. But the ship could just as easily be full of disciplined soldiers* or a religious/political splinter group. A group of colonists intending to be future neighbors will have long memories. Its also possible that these travelers are sponsored by someone else, and the sponsor may have an unusual hold or ability to organize them.

Or the culture of travel might be different from place to place.

RyanW 01-03-2018 10:29 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by ericthered (Post 2147288)
A group of colonists intending to be future neighbors will have long memories.

On the other hand, if they are leaving behind an existing power structure, there will likely be people intending to get a head start at creating a new one, with them at the top.

ericthered 01-03-2018 10:35 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by RyanW (Post 2147292)
On the other hand, if they are leaving behind an existing power structure, there will likely be people intending to get a head start at creating a new one, with them at the top.

Quite so. But that looks qualitatively different from accosting people you'll never see again. Not that its any less unpleasant, but that its yet another variation.

kreios 01-06-2018 10:25 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by FTL Travel Revisited
A more detailed look at the FTL mechanics, introducing changes, and computing orbits.

Continue reading...

ericthered 01-09-2018 10:07 AM

Re: [Blog] n-Body Politics
 
Ahh, you got rid of the moons! Which is very understandable. Shape the setting the way you want it to go. And its a very elegant fix. It has the side effect of making Jupiter's moons possible but expensive to visit.

I didn't follow the fast transfer orbits section. is a acceleration or is it the average of perapsis and apoasis again? and is 'v' sub 'a' half of the additional delta-v you're spending?

kreios 01-13-2018 12:51 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by ericthered (Post 2148818)
Ahh, you got rid of the moons! Which is very understandable. Shape the setting the way you want it to go. And its a very elegant fix. It has the side effect of making Jupiter's moons possible but expensive to visit.

Yup. Most of the time, working out the mechanics makes it easier to "naturally" achieve the effect you want to achieve.
Of course, in this case, I could directly set the gravitational bound, so it was even easier.

Quote:

I didn't follow the fast transfer orbits section. is a acceleration or is it the average of perapsis and apoasis again? and is 'v' sub 'a' half of the additional delta-v you're spending?
That's unfortunate. I've added a sentence hopefully clarifying that I'm repeating the formula from above again (and yes, a is again the semi-major axis; I'm assuming almost-instant acceleration. v_a is the additional dV I want to spend)

kreios 01-13-2018 01:13 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Space Combat Iteration 1: Low Earth Orbit
Having decided on the general technology available in-setting, we can now look at how space combat is going to look like.

For this, letís take the spacecraft from GURPS Spaceships 8: Transhuman Spacecraft. Specifically, letís first take the Predator AKV from page 12. Exchanging the drive to a water fusion torch increases acceleration to 4.5G, and delta v to 45km/s, for a burn time of slightly over eleven minutes. This also increases cost to about $17M. Iím using armour-as-dice, so they have 15d/6d/9d armour.

The next spacecraft is one of the smaller SDVs: The EUís Hermann Oberth SDV (page 30). Replacing the drives as above gives it an acceleration of 3G and a delta v of 60km/s. Armour is 24d/6d/6d. Normally, thatíd include four Predator AKVs.

Continue reading...

A first - if fairly small - look at space combat as written in an example scenario.

kreios 01-20-2018 12:25 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Space Combat Iteration 1: Deep Space
Since last time, we admittedly suffered from sub-optimal engagement decisions by the SDV, weíll now be looking at a more reasonable scenario.

Now, the same officer-in-training who had failed the previous scenario is allowed a repetition. This time, he decides to try another approach: Heís taking the Oberth to a highly-eccentric orbit, timed to reach apogee just as the AKVs get close. This minimizes the relative engagement velocity.

Continue reading...

ericthered 01-22-2018 10:14 AM

Re: [Blog] n-Body Politics
 
I wonder how the last battle would have went if the Oberth targeted the missiles with lasers and trusted its own kinetics (with proximity explosions) to keep them from ramming it.

kreios 01-22-2018 02:36 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by ericthered (Post 2152140)
I wonder how the last battle would have went if the Oberth targeted the missiles with lasers and trusted its own kinetics (with proximity explosions) to keep them from ramming it.

Which missiles? Only four AKVs (and the SDV) were involved in the battle, and the Oberth targeted the AKVs.

(The next battle will involve missiles, though)

ericthered 01-22-2018 02:51 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by kreios (Post 2152213)
Which missiles? Only four AKVs (and the SDV) were involved in the battle, and the Oberth targeted the AKVs.

(The next battle will involve missiles, though)

Your electromagnetic guns. Those are conventional shells that are quite vulnerable to laser fire, particularly if you have several rounds to shoot at them, as they really don't dodge. I usually call them missiles because if you read the description on SS28 they actually have propulsion systems on them, just not the same as a missile.

kreios 01-22-2018 03:08 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by ericthered (Post 2152218)
Your electromagnetic guns. Those are conventional shells that are quite vulnerable to laser fire, particularly if you have several rounds to shoot at them, as they really don't dodge. I usually call them missiles because if you read the description on SS28 they actually have propulsion systems on them, just not the same as a missile.

That makes quite sense, and I had forgotten about PD fire against shells. This'll probably be my next post then, though I'm probably going to introduce rapid-fire guns for that.

kreios 01-28-2018 10:18 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Space Combat Iteration 1: Variations
We did test the space combat system. But this was only one configuration of weapons - what other things can we change?

Continue reading...

Features point defence, particle beams, and missiles.

Humabout 01-28-2018 11:08 AM

Re: [Blog] n-Body Politics
 
What are you trying to accomplish with this analysis exactly? It feels like you're trying to see what sort of gameplay using everything in GURPS Spaceships dictates instead of letting your design goals dictate which parts of GURPS Spaceships you should use. For four worked examples of the latter approach, check out So You Want to Build a Spaceship... in Pyramid #3/94 - Spaceships III.

kreios 01-29-2018 01:54 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Humabout (Post 2153824)
What are you trying to accomplish with this analysis exactly? It feels like you're trying to see what sort of gameplay using everything in GURPS Spaceships dictates instead of letting your design goals dictate which parts of GURPS Spaceships you should use.

Actually, I'm trying to do it the other way around - I have a set of rough design goals (or maybe a 'feeling of how it should look like'). However, I have difficulties going from the abstract design choices (types of weapon allowed, space drives, etc) directly to (a) how this changes the feeling of space combat and (b) how it influences space combat doctrine. And if I don't think about it, a player could end up slaughtering military forces with ease.

Going away from the abstract musings, consider the following: I like the concept of AKVs as a kind of networked and distributed lethality and as the extension of the cruise missile concept. For AKVs to be viable, several factors are necessary: They must be fairly difficult to intercept (otherwise they're toothless) and ramming must feature as a sometimes-necessary tactic (otherwise, they're a bit boring). Accordingly, damage of normal weapons shouldn't be able to vapourize any enemy spacecraft.

Another example: The last playtest showed that particle beams are a very useful secondary anti-AKV weapon. I'd have defaulted to lasers without gaming it out.

Quote:

For four worked examples of the latter approach, check out So You Want to Build a Spaceship... in Pyramid #3/94 - Spaceships III.
I have, and especially Working Stiffs is an inspiration to me (it's actually mentioned in the first post :-) )

Humabout 01-29-2018 04:29 PM

Re: [Blog] n-Body Politics
 
I guess what I'm getting at is that you're still taking everything as it is written in the books. If you want guns to have a certain feel, just change their stats so they meet your needs. Deciding weaponry and technology based on what works in RAW Spaceships combat may be contrary to your overall setting goals.

Humabout 01-29-2018 04:38 PM

Re: [Blog] n-Body Politics
 
Further thoughts!!

So first the bad news: As long as I can pack more energy into a weapon - including k8netic energy - I can eventually vaporize anything I hit. This suggests you might look at how AKVs can NotGetHit (tm). Options include enhanced vehicular dodge, large ships have triuble tracking small ships, or stealth. None of these sre realistic, but they would be necessary for your purposes.

Tell me, do you see AKVs more as fighters or torpedo boats?

kreios 01-30-2018 02:42 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Humabout (Post 2154112)
I guess what I'm getting at is that you're still taking everything as it is written in the books. If you want guns to have a certain feel, just change their stats so they meet your needs. Deciding weaponry and technology based on what works in RAW Spaceships combat may be contrary to your overall setting goals.

Oh, I definitely will. This is currently for testing an actual implementation of everything. The next step (which has been partly written) will be modifications (HP, for example)

Quote:

Originally Posted by Humabout (Post 2154117)
Further thoughts!!

Always glad for them.

Quote:

So first the bad news: As long as I can pack more energy into a weapon - including k8netic energy - I can eventually vaporize anything I hit. This suggests you might look at how AKVs can NotGetHit (tm). Options include enhanced vehicular dodge, large ships have triuble tracking small ships, or stealth. None of these sre realistic, but they would be necessary for your purposes.
True, more energy will always mean more damage. However, there are disadvantages even without introducing rules changes (which I might still do too). As an example: Assume an SM+8 spacecraft can mount a major battery which can threaten AKVs. Alternatively, an SM+10 spacecraft's major battery vapourizes them. But I can attack the latter with ten times the number of AKVs to get the same cost-benefit ratio. So there's a clear tradeoff between those two.

Quote:

Tell me, do you see AKVs more as fighters or torpedo boats?
Interesting question. I guess at the moment, I see them as a combination of two different roles: (a) In peacetime and against lightly-armoured opponents, they extend the effective range of spacecraft. (b) Against well-defended opponents, they are self-defending missiles.
I guess an analogy might be a kamikaze drone with submunitions which usually returns to be rearmed.
Or, to stay with naval terminology, maybe an unmanned PT boat with an additional spar torpedo which detonates a few tons of explosives in the boat?

(E) 01-30-2018 04:21 PM

Re: [Blog] n-Body Politics
 
Scott Westerfeld has written "the risen empire" and "the killing of worlds" the space combat in those books has some parralels with gurps' eggshell space ships.

One aspect of the combat in that series is the use of detached armour. Basically a large chunk of metal is detached from a vessel and kept between the vessel and the enemy.
Variations on this idea might include things like a solar sail that is used for concealment.

Humabout 01-30-2018 11:55 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by kreios (Post 2154334)
True, more energy will always mean more damage. However, there are disadvantages even without introducing rules changes (which I might still do too). As an example: Assume an SM+8 spacecraft can mount a major battery which can threaten AKVs. Alternatively, an SM+10 spacecraft's major battery vapourizes them. But I can attack the latter with ten times the number of AKVs to get the same cost-benefit ratio. So there's a clear tradeoff between those two.

Oh I just point out that wanting to avoid instagibbing AKVs as a goal isn't necessarily feasible outright. Someone can always make a big enough gun for that. With that said, other limiting factors, like one big gun vs. lots of little ones, will come into play. This still begs the question: If I can make one really big gun that can pink-mist AKVs and bang up big ships at long ranges, why use AKVs that will get pink-misted by the enemy when I can just shoot him in the face myself?

One answer might be that he has a really big pink-mist-making gun, too. I'd rather send in a swarm of AKVs, hope one or two get through, and stay the heck out of his range. Another might be that AKVs are cheap enough that it's more economical to risk a swarm of them instead of putting my mothership at risk.

This is all just food for thought.

Quote:

Originally Posted by kreios (Post 2154334)
Interesting question. I guess at the moment, I see them as a combination of two different roles: (a) In peacetime and against lightly-armoured opponents, they extend the effective range of spacecraft. (b) Against well-defended opponents, they are self-defending missiles.
I guess an analogy might be a kamikaze drone with submunitions which usually returns to be rearmed.
Or, to stay with naval terminology, maybe an unmanned PT boat with an additional spar torpedo which detonates a few tons of explosives in the boat?

Well, the reason I ask this is because airplanes and boats operate very differently within a naval battle. Aircraft are, by the nature of the medium in which they operate, faster and more maneuverable. They also have to be lighter, meaning they get destroyed really easily when you do hit them.

Boats, on the other hand, take a walloping and still don't sink, but they are slower, less maneuverable, and easier to hit. A torpedo boat is small and maneuverable compared to a dreadnought, but it is far easier to hit than a dodgy kamakaze zero, at least in movies (which I'm using a common point of reference for the sake of discussing feel).

If you are going more for the airplanes vs. naval ships feel, I'd suggest reading Planet-Hopping with the 273rd Fleet in So You Want to Build a Spaceship... It addresses mechanical changes to make some spaceships feel like airplanes and others like naval vessels.

On an unrelated side note, naval vessels in WWI and WWII generally took around 10 or 12 torpedo hits to actually sink. That's a nice benchmark for how fast you want your big spaceships to die (fewer hits and you get more like Cold War-era and modern naval warfare; more hits and it's more like Age of Sail broadsides).

kreios 02-03-2018 02:13 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by (E) (Post 2154367)
Scott Westerfeld has written "the risen empire" and "the killing of worlds" the space combat in those books has some parralels with gurps' eggshell space ships.

One aspect of the combat in that series is the use of detached armour. Basically a large chunk of metal is detached from a vessel and kept between the vessel and the enemy.
Variations on this idea might include things like a solar sail that is used for concealment.

I'll look those up.
With regards to the detachable armour, I don't think there's much of an advantage compared to regular or reactive armour.


Quote:

Originally Posted by Humabout (Post 2154465)
One answer might be that he has a really big pink-mist-making gun, too. I'd rather send in a swarm of AKVs, hope one or two get through, and stay the heck out of his range. Another might be that AKVs are cheap enough that it's more economical to risk a swarm of them instead of putting my mothership at risk.

Agreed - and it will take some tweaking to get everything nicely calibrated.



Quote:

Well, the reason I ask this is because airplanes and boats operate very differently within a naval battle. Aircraft are, by the nature of the medium in which they operate, faster and more maneuverable. They also have to be lighter, meaning they get destroyed really easily when you do hit them.

Boats, on the other hand, take a walloping and still don't sink, but they are slower, less maneuverable, and easier to hit. A torpedo boat is small and maneuverable compared to a dreadnought, but it is far easier to hit than a dodgy kamakaze zero, at least in movies (which I'm using a common point of reference for the sake of discussing feel).

If you are going more for the airplanes vs. naval ships feel, I'd suggest reading Planet-Hopping with the 273rd Fleet in So You Want to Build a Spaceship... It addresses mechanical changes to make some spaceships feel like airplanes and others like naval vessels.
I actually think that the airplane/ship distinction of the current sea combat (and by extension WW2 sea combat, and by extension also the 273rd Fleet article) is quite exactly that which I want to avoid. No different mediums to move through, and probably little dodging. Let's see whether I actually manage to do that, though.

Quote:

On an unrelated side note, naval vessels in WWI and WWII generally took around 10 or 12 torpedo hits to actually sink. That's a nice benchmark for how fast you want your big spaceships to die (fewer hits and you get more like Cold War-era and modern naval warfare; more hits and it's more like Age of Sail broadsides).
That's probably a good reference number, thanks.

kreios 02-11-2018 03:21 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Space Combat Iteration 2: Rules
The original space combat system test showed some issues. How do we fix them? For now, by importing 3e's system.

Continue reading...
First go at customizing the Spaceships system.

Apologies for the non-weekly update. I had thought my queue of posts to last a bit longer...

Humabout 02-11-2018 07:05 PM

Re: [Blog] n-Body Politics
 
Why don't ypu have to roll to hit with a speed of light weapon? You still have to point it at the target effectively. If an argument exists to remove rolls, it's the Active Defense roll, but Kromm has said repeatedly that even that is a measure of the target's evasiveness - not him literally dodging. This is why Dodge is allowed against guns and lasers and such in RAW.

Also, why does a railgun have a range at all? There isn't any appreciable drag to slow a projectile until it hits something. Its range is infinite with the caviat that ships can use objects as cover.

kreios 02-12-2018 02:42 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Humabout (Post 2157699)
Why don't ypu have to roll to hit with a speed of light weapon? You still have to point it at the target effectively. If an argument exists to remove rolls, it's the Active Defense roll, but Kromm has said repeatedly that even that is a measure of the target's evasiveness - not him literally dodging. This is why Dodge is allowed against guns and lasers and such in RAW.

That's actually an artifact from 3e's rules which I hadn't well clarified (the corresponding part has been updated). Essentially, in 3e's THS (p. 197) specified a to-hit roll; however, on failing, you still did half damage. In the interest of keeping it simple, I kept those rules for now.

Quote:

Also, why does a railgun have a range at all? There isn't any appreciable drag to slow a projectile until it hits something. Its range is infinite with the caviat that ships can use objects as cover.
I've also edited in a clearer explanation for that in the blog. Essentially, what I'm looking at isn't maximum range, but range in which I can guarantee a hit. Essentially, at 75 kilometres, you cannot avoid a projectile closing in at 15km/s with 0.5G.

In writing this, I also added a completely new section on guided railgun projectiles - and, spoiler alert, they're extremely nice!

Humabout 02-12-2018 08:34 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by kreios (Post 2157929)
Essentially, what I'm looking at isn't maximum range, but range in which I can guarantee a hit.

But by Kromm's own posts and comments, Dodge represents moving erratically to force a miss. It's an abstraction. Similarly, the skill roll to hit is to see if you are sufficiently on target to potentially score a hit against an unaware or non-defending target. Of course all of this assumes you're using 4th edition rules, and as of the your last post, it looks like you're playing 3rd edition THS. So that might by moot.

kreios 02-13-2018 01:51 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Humabout (Post 2157998)
But by Kromm's own posts and comments, Dodge represents moving erratically to force a miss. It's an abstraction. Similarly, the skill roll to hit is to see if you are sufficiently on target to potentially score a hit against an unaware or non-defending target. Of course all of this assumes you're using 4th edition rules, and as of the your last post, it looks like you're playing 3rd edition THS. So that might by moot.

I may have overshot there - my original intention with that range computation was to replicate SS3's tactical system's "guaranteed dodge", i.e. not being in the same hex as the salvo. However, I then decided to just compute when you wouldn't be able to dodge at all - even a ten-kilometre hex would take almost two turns to clear (i.e. a range of 540 kilometres from rest).

However - this brought me towards another idea (thanks for that!). We do have rules for long projectile flight durations, specifically from Tactical Shooting (p. 32 [i]Bullet Travel]). It tells us to take 1d-5 per additional second and apply the result as a modifier to the skill roll.

Now, for some Fermi Estimation: A human being is about two metres high. A spacecraft has roughly the same aspect ratio as a human being. A human moves at about 6m/s (according to the GURPS rules).
Let's take an SM+12 spacecraft (200m long) accelerating at 1G. At 20 second-turns, it can change its position by 2000 metres, which is 10x its length.
In a one-second combat turn, a human can change their position by about 3x their length.
Accordingly, we can use the following rule: Roll 1d-5 per two full combat turns a projectile attacking a spacecraft has been in flight and apply that value as a modifier to the attack roll. Modify this time by the following: Divide it by the square root of the spacecraft's acceleration, and divide it by two for every two SM you're smaller than SM+10.

As an example:
The modified Predator AKV I've been using (SM+6, 4.5G) divides that time by 2 (from acceleration) and by 4 (4 SM smaller than 10), i.e. you roll 4d-20 per turn it takes for the projectile to reach you.

The modified Oberth SDV (SM+9, 3G) divides the time by 2 (from acceleration; it's a rough estimate), i.e. you roll 1d-5 per turn.

Hm. While I like the general idea (because it nicely abstracts out relative velocities, for example), the numbers do seem a bit strange. But wait - I have the Hnd numbers available! So, take Hnd into account (representing size and reorientation for the main drive to propel you into a different direction)? In this case we can multiply it by 0.5 (Hnd 0), 1 (Hnd -1), 2 (Hnd -2) and 4 (Hnd -3)

That would give the AKV 2d-10 per turn and the SDV 1d-5. That seems nicer, and I'm looking forward to gaming it out.

Although I might apply this as a bonus to dodge instead, since that would mean that multiple projectiles (restricting your dodge vector) make it much more difficult to dodge than a single projectile.

(Well, that post went kind-of-rambly.)

Humabout 02-13-2018 07:31 PM

Re: [Blog] n-Body Politics
 
Something else to consider:

Lasers aren't instant-speed-of-light weapons. They have to send some sort of initial ranging pulse so they can adjust their focal array so that the laser beam is at maximum focus on the target. This takes 2 * [Distance in Light-Seconds] / [1 Light-Second per Second] to range the target and fire the weaponized laser. The weaponized laser then takes another [Distance in Light-Seconds] / [1 Light-Second per Second] to reach the target. Adding these and simplifying units, we find that it takes 3 * [ Distance in Light Seconds ] seconds to from pressing the fire button to the target getting hit. That generally won't be much time, but space is big and ranges might be large. Let's see what sort of limits exist for ability to dodge.

The target can probably detect the ranging ping (or it's really in for a cruel surprise), so let's just assume it can. This gives the target 2 * [Distance in Light-Seconds] seconds between getting pinged and getting hit. That's how long the target ship has to react to the ping and dodge.

Next, let's take a look at two cases: (1) Human doing the dodging and (2) computer doing the dodging.

(1) Human Dodging.
An average human takes about 0.25 seconds for visual stimulus, 0.17 seconds for audial stimulus, and 0.15 seconds for tactile stimulus, as per random Google result I'm not taking the time to vet. It doesn't sound horribly off. That suggests that depending on the warning system, the pilot will have different lengths of time to react and dodge. This mean that any shot within 0.25 light-seconds for visual warning, 0.17 light-seconds for audial warning, or 0.15 light-seconds for tactile warning probably shouldn't allow any dodge that requires pilot input other than general evasive maneuvers.

(2) Computer Dodging.
This is very hardware and software dependent. Currently, (by similar unvetted Google search), computers are alleged to have comparable reaction times as humans, but you don't have TL 8 computers. You have high-TL sci-fi computers, so can probably set this arbitrarily fast, meaning a computer can always attempt to dodge a laser weapon.

Next step is factoring in the responsiveness of the ship itself. This is quite a bit harder to do, since it is so very dependent on the specific ship. Here, you probably want to just pick a number of seconds that sounds reasonable. - you mentioned humans dodge 3 * Height, so that's one measure. But really when you think about it, the ship never has to move more than half it's longest dimension get out of the way of a shot. How long does this take? That's pretty simple:

t = sqrt(2 * distance moved / acceleration)

or for our purposes

t = sqrt{[Ship Length in Meters] / (9.81 * [Ship Acceleration in Gs])}

We add this time to the reaction time of whoever is dodging to get the total time to dodge. If this is less than 2 * [Distance to Target in Light-Seconds] seconds, the target can attempt to dodge. If not, the target just gets hit.

It's also worth noting that a spaceship can simply rotate out of the way, as well, but this is very geometry-dependent. At best, it's nearly instantaneous, and at worst, it takes too long. That sounds silly to mention, but GURPS doesn't give enough details to narrow the domain any further. It does, however, provide you with a way to fudge numbers in the target's favor, if that's the flavor you want.

WORKED EXAMPLE
A SM+12 ship is 200 m long and has a maximum acceleration of 1 G. This means that it takes the ship

t = sqrt{[200] / (9.81 * [1])} = 4.52 seconds to clear a worst-case attack.

Let's assume it is piloted by a human receiving visual warnings of inbound attacks, resulting in a 0.25 second reaction time. This means the target needs at least 4.77 seconds of warning to have a chance of successfully dodging. We know the target has 2 * [Distance in Light-Seconds] seconds to dodge, so we can then set this equal to 4.77 seconds to find that any shot fired within 2.385 light-seconds or 715,005 km has a chance to prevent the target from dodging a shot aimed at the dead middle of the ship. At the other end of the spectrum, a shot fired at the very edge of the end of the ship would need to have a range of 0.125 light-seconds or 37,474 km to deny the pilot time to even react.

Note: A computer wouldn't have that reaction time to worry about and could always dodge, and could dodge a hit amidship fired from beyond 2.26 light-seconds (677,531 km) or any shot at its extreme edge. This suggests AI have the advantage at close ranges, but aren't necessarily superior at longer ranges.

Also, This assumes the attacker already knows of the target's existence. Add another [Distance in Light-Seconds] seconds to find the time from detection to hit, assuming the attacker fires as soon as the target is spotted. Add 2 * [Distance in Light-Seconds] seconds to the target's allowable reaction time if the target was detected via active sensors and detected the ping (probably a safe assumption for military craft).

[EDIT]
And having written all of that, I realize that it ignores the "Dodge includes moving erratically to avoid being hit" thing. It does, however, provide a hard line where Dodge no longer can represent an actual reaction to an attack. If you don't mind the added complication, you could apply Restricted Dodge Against Firearms from Tactical Shooting, p. 17 with awareness determined by range to target as shown above. And those range thresholds can be pre-calculated for ships, so you don't have to do them on the fly.

doctorevilbrain 02-13-2018 09:53 PM

Re: [Blog] n-Body Politics
 
A Human being is 2 meters tall?! Where the National Basketball Association? It ignores the fact that each sex has different average heights. Different countries have different average heights too. I don't understand why somebody would say that without acknowledging the difference.

Humabout 02-14-2018 04:43 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by doctorevilbrain (Post 2158285)
A Human being is 2 meters tall?! Where the National Basketball Association? It ignores the fact that each sex has different average heights. Different countries have different average heights too. I don't understand why somebody would say that without acknowledging the difference.

Sexual dimorphism and astounding accuracy are pretty counter to the purpose of doing a Fermi Estimation (click the link). All humans are on the order of 2 meters tall in just as all SM +12 spaceships are on the order of 200 meters long. His Fermi estimation holds.

doctorevilbrain 02-14-2018 07:41 PM

Re: [Blog] n-Body Politics
 
I really don't care. I haven't changed my mind about what I said.

kreios 02-15-2018 03:36 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Humabout (Post 2158261)
[snip calculations]

Interesting point, although I am wondering whether you actually need ranging pings - you probably can get a fairly decent fix just by using passive sensors (or just ping several times per second; modern LIDARs like the high-end Velodynes already produce a few hundred thousand datapoints per second (granted, that's 360į). And, once you have the distance to the target determined to within a kilometre or so, do you actually lose much efficiency compared to a centimetre-exact distance?

Of course, the longest-range lasers I have have a 1/2d-range of 20,000 kilometres, meaning we have times measured on the order of 0.1 seconds.

Quote:

(2) Computer Dodging.
This is very hardware and software dependent. Currently, (by similar unvetted Google search), computers are alleged to have comparable reaction times as humans, but you don't have TL 8 computers. You have high-TL sci-fi computers, so can probably set this arbitrarily fast, meaning a computer can always attempt to dodge a laser weapon.
A computer, even today, should be able to get you some sort of dodging software within milliseconds. Assuming you have recognized a laser through some sort of heat detection, you should be able to propagate that information directly to the RCS and/or drive systems. I could probably write something like that today (if you give me the interface) that's limited by engine speed, not computation power.

Quote:

[EDIT]
And having written all of that, I realize that it ignores the "Dodge includes moving erratically to avoid being hit" thing. It does, however, provide a hard line where Dodge no longer can represent an actual reaction to an attack. If you don't mind the added complication, you could apply Restricted Dodge Against Firearms from Tactical Shooting, p. 17 with awareness determined by range to target as shown above. And those range thresholds can be pre-calculated for ships, so you don't have to do them on the fly.
That's a good idea. I'll have to see whether it adds anything to the game itself except for additional rolls, but it would be a start. Hm, I have the feeling I'm Tactical Shooting will soon become my second-most referred-to book...



Quote:

Originally Posted by doctorevilbrain (Post 2158285)
A Human being is 2 meters tall?! Where the National Basketball Association? It ignores the fact that each sex has different average heights. Different countries have different average heights too. I don't understand why somebody would say that without acknowledging the difference.

As Humabout noted, it's a Fermi estimate, meaning I'm actually happy if I'm within 50% or so of the target. You'll note that the other values are average human speed (6m/s, which is higher than GURPS average of 5y/s = 4.5m/s), a human and a spacecraft having the same aspect ratio (I don't even know what the aspect ratio of a spacecraft is, maybe 5:1?), and even G at 10m/s.

But, looking at the relation between height and speed, we have 3s (original estimate), 2.7s (165cm for median female height from wikipedia plus 5y/s from GURPS average), and 2.57s (ditto for male height). Meaning I'm still within less than 20% and, in my opinion, perfectly fine.

Remember - everything's an abstraction, and in the end, what counts is getting rules that aren't too disbelief-inducing.

Humabout 02-16-2018 05:53 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by kreios (Post 2158837)
Interesting point, although I am wondering whether you actually need ranging pings - you probably can get a fairly decent fix just by using passive sensors (or just ping several times per second; modern LIDARs like the high-end Velodynes already produce a few hundred thousand datapoints per second (granted, that's 360į). And, once you have the distance to the target determined to within a kilometre or so, do you actually lose much efficiency compared to a centimetre-exact distance?

Well, a kilometer or two can be quite a lot. Lasers work because they are highly focused, and I've heard of cutting lasers not doing anything useful if their focal length is minute fractions of a percentage off. Really, though, Luke Campbell is the better person to speak to actual tolerances.

That said (and linked), remember that as soon as you use any active sensor to ping the target, they know about you and should be assuming you're going to pull the trigger as soon as the signal gets back to you. This basically starts the Dodge Clock ticking and sets a minimum time limit - and consequently a maximum undodgeable range - on speed-of-light weapons. Nothing says the pilot isn't asleep at the wheel or his reflexes kind of suck. But those sorts of things are determined through surprise rolls and active defense rolls.

It also tells you that the most weapons will attempt to extend their range to that point, but the number that try to exceed it will drop off due to reduced efficacy. I'd expect the typical range of space-based weapons to be something like a skewed Guassian distribution with the mean around the maximum undodgeable range and weighted toward the undodgeable side, since that's the more effective side of things. Of course, super-long-range lasers are still plenty effective against unsuspecting, unpowered, or particularly unmaneuverable craft.

Quote:

Originally Posted by kreios (Post 2158837)
A computer, even today, should be able to get you some sort of dodging software within milliseconds. Assuming you have recognized a laser through some sort of heat detection, you should be able to propagate that information directly to the RCS and/or drive systems. I could probably write something like that today (if you give me the interface) that's limited by engine speed, not computation power.

I'm not really surprised. It looked pretty high, but I wasn't vetting anything when I grabbed the number, and we all know how reliable the internet is. Either way, even if it is that high, somehow, it wouldn't break my suspension of disbelief for futuristic computers to do this effectively instantly.


Quote:

Originally Posted by kreios (Post 2158837)
That's a good idea. I'll have to see whether it adds anything to the game itself except for additional rolls, but it would be a start. Hm, I have the feeling I'm Tactical Shooting will soon become my second-most referred-to book...

That rule doesn't add any rolls to the attack resolution sequence. It just limits defenses in specific ways for certain weapons.

kreios 02-18-2018 11:08 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Space Combat Iteration 2: Playtest Intercept
Letís playtest everything again! Weíll use the same scenario as beforehand, and simply use the new rules.

Continue reading...

kreios 02-25-2018 12:24 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Space Combat Iteration 2: Playtest SDVs
Similar to last time - except now, weíll pit two SDVs against each other. Specifically, two modified Oberth-class SDVs from last time. Iíll remove the one multi-purpose system from the front and replace it with a full-sized weapon system: Either a railgun or a particle beam.

Continue reading...

kreios 03-04-2018 01:15 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Space Combat Iteration 2: Ground Fire
Now that we have achieved orbital superiority, the planetís surface is no longer out of bounds - time for orbit-to-ground fire!

Continue reading...

A look at ortillery fire (using rules from High Tech), efficient orbital bombardment munitions, anti-orbital railgun tanks, and submerines.

kreios 03-18-2018 01:24 PM

Re: [Blog] n-Body Politics
 
Since I forgot to post the link last week (though it got hit by GurpsDay), here's a double feature of Planetary Invasion posts:

Quote:

Originally Posted by Planetary Invasion
As weíve seen last time, thereís sort of a Mexican standoff in space: Spacecraft are vulnerable to ground fire, but planetary defences can be killed fairly easily by orbital bombardment. This, by the way, fits with the ďif you can see it, you can kill itĒ which seems to have been the military trend of the last few decades.

This implies that spacecraft can hang back (such that they can dodge incoming shots) and slowly search for any suspicious ground craft which they then bombard (using the fact that those railgun tanks cannot dodge as well as spacecraft). But this cannot kill any submarines or tanks lying low (a fuel cell or MHD turbine tank thatís idling will be almost invisible).

So - are the spacecraft screwed? I donít think so.

Continue reading...

Quote:

Originally Posted by Planetary Invasion: Logistics
An army marches on its stomach, as somebody (the quote is attributed to both Napoleon and Friedrich II) once said. Accordingly, letís take a very rough look at the logistics of a planetary invasion.

Iím saying a very rough look because, ultimately, we donít yet know what kind of technology is used, and this will change the number. But, for now, since we just want a rough estimate, Iíll be using roughly modern supply numbers.

Continue reading...

kreios 03-25-2018 10:12 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Air Combat
Weíve looked at space combat, and weíve looked at how to get people down onto the surface. But how do they fight once on the surface? Specifically, how does air combat look like?

Continue reading...

A very short look into air combat, looking at ground-to-air fire, engine choices, and very fast fighter craft.

johndallman 03-25-2018 11:17 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by kreios (Post 2167646)
A very short look into air combat, looking at ground-to-air fire, engine choices, and very fast fighter craft.

Flying nap-of-earth with a fusion torch at Mach 5 is going to damage anything on the surface that isn't armoured. I'd also worry about detection via the IR from your fusion torch being seen from orbit, reflected back off clouds, and the like.

kreios 03-25-2018 03:09 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by johndallman (Post 2167659)
Flying nap-of-earth with a fusion torch at Mach 5 is going to damage anything on the surface that isn't armoured.

Quite possibly, and I should sit down and actually compute that at some point.

Quote:

I'd also worry about detection via the IR from your fusion torch being seen from orbit, reflected back off clouds, and the like.
Excellent point. A napkin calculation gives me roughly +11 for jet/stealth hull vs 25 for the fusion torch, both before sensor bonus and range. Accordingly, for a normal SM+10 craft (+9 from sensors), that's a 50/50 detection range of 5 kilometres vs 1,000 kilometres - suggesting that, indeed, my analysis is wrong when considering orbital detection. I'll update the post in the next few days.

kreios 04-03-2018 05:46 AM

Re: [Blog] n-Body Politics
 
I had updated the post a few days ago, adding
Quote:

Edit As an addition to the original analysis, johndallman over at the gurps forums, pointed out two things: (a) A fusion torch flying close to the ground will do quite a bit of damage to the ground, and (b) it will be easily visible from orbit. Iíll ignore point (a) for now, since the same thing applies to landing shuttles. (b) is quite relevant - the fusion torch fighter will be visible at +25, before sensor bonus and range malus. This is sufficient for a detection range from a 1,000 kilometre orbit for a normal SM+9 spacecraft. Kinetic strikes will follow shortly after.
plus a stealth fighter build.

Additionally: New post!

Quote:

Originally Posted by Armoured Vehicles
Now that weíve looked at aerial combat, weíll follow this up with a short post on vehicle combat - and one thatíll bring us even closer to the limitations of the Spaceships system.

Letís start by looking at two different vehicles: The tank and the infantry fighting vehicle.

Continue reading...

A short example of two vehicles (IFV, Tank) and infantry weapons capable of hurting them.

kreios 04-08-2018 04:33 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by Infantry Combat
Having looked at vehicle combat last time, weíll now have an example combat on the ground between two parties: One battlesuit-armoured, the other light infantry.

Continue reading...

Example infantry combat, which turns out to not work well even with rules adaptions.

The_Ryujin 04-09-2018 07:29 PM

Re: [Blog] n-Body Politics
 
Can't believe I'm just finding out about your blog (blarg... I've really gotta get out of my slump heh). So far I'm really liking what I'm seeing, keep it up!

Also I've noticed you're having some trouble getting getting Spaceships to line up with what you want and find HEMP a bit to powerful.

Well here are a few posts from my blog I think might help you:

This post hacks the Spaceships system to let you make ships of any size or weight.

A few ways to make vehicles made with the spaceships system more survivable.

This one hacks how Ultra-Tech scales the different warhead options it offers.

And here's my take on how to handle reactive armor in 4th edition to give battlesuits a bit more suitability on the Ultra-Tech battlefield.

I'm also trying to get back to updating my blog and one of the posts I'm working on will cover stronger, military grade armor options for Spaceships that give better and laminated dDR for TL10+ options but at the trade of having higher costs. So hopefully I'll have that one finished soon.


Edit:
Already finished heh

kreios 04-10-2018 07:34 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by The_Ryujin (Post 2170463)
Can't believe I'm just finding out about your blog (blarg... I've really gotta get out of my slump heh). So far I'm really liking what I'm seeing, keep it up!

Thank you.

Quote:

Also I've noticed you're having some trouble getting getting Spaceships to line up with what you want and find HEMP a bit to powerful.
Indeed, although I have a few posts which are coming closer to that in the backlog.

Quote:

Well here are a few posts from my blog I think might help you:
*snip*
Thanks! I had already read most of them, but that was quite some time ago. You'll actually find a few similarities in my own posts, for example the structural reinforcement (although my version gives even more HP). In the end, I believe my solution might look a bit different - for HEMP, look for next week's post :-)

The_Ryujin 04-10-2018 12:44 PM

Re: [Blog] n-Body Politics
 
Cool stuff, can't wait to see what you got.

Also, here's my crack at a 70 ton TL10 MBT, note I used my Structural Reinforcement rules for it since I worked on this before your reply and my HR on APEP rounds that brings them more in line with the ammunition modifiers in High-Tech and they only increase cost by 7, not 10 times.

It has 1 110mm main railgun, 2 15mm point defense railguns and the ability to hold a drone that weighs up to 1.2tons. It's driver section has two holographic workstations and a C6 mainframe. At the rear it has two more holographic workstations for the drone operations crew.

It's frontal armor is made of two layers of Diamondoid Laminate sandwiched between three layers of Advanced Nano-Laminate and counts as having double dDR vs shaped charge and plasma attacks. The rest of the tank has conventional Nanocomposite.

Other then this, it follows the basic plan of your 100ton MBT.

Code:

TL Vehicle    dST/dHP  Hnd/SR  HT  Move  LWt.  Load  SM  Occ.  dDR    Range  Cost      Loc.  Notes
10 70ton MBT  26/42  -3/5  13  3/30  70  1.6  +5  2+2SV  233/45  504 $12.2M  2C1T2t  [1]
[1]Has dDR 233 on the front vehicle arc that counts as laminated, dDR on the sides, dDR on top, dDR 25 at the rear, and dDR 20 on he bottom.

The 110mm main gun does 7d◊8(3) pi++ dDamamge, and has range 17,000/130,000 with APEP or 3d◊11 pi++, range 8,600/65,000 with basic ball ammo. The cannon has ROF 1, ST 71M, bulk -13, rcl 3 and holds 133 rounds that weigh 53lbs each.

The two 15mm point defense railguns do 4d+2(2) pi dDamage, and range 100,000/250,000 with APEP or 2d+1(2) pi dDamage, range 50,000/130,000 with basic ball ammo. The guns have ROF 20, ST 49M, bulk -11, rcl 2, and holds 120 rounds per gun that weigh 30lbs each.

Note that the 30lbs per shot for the point defense guns came from running the number with how Spaceships scale things, I personally think that's kinda overkill heh. Also the range figures a semi-fudged. I run some funky numbers to get my EM gun spreadsheet to give me rounds that would weigh as much as what Spaceships lists and the variables effect range. They're probably not too far off though and as you can see, the ranges at a point they almost don't matter in ground combat.

kreios 04-14-2018 11:30 AM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by The_Ryujin (Post 2170594)
Also, here's my crack at a 70 ton TL10 MBT, note I used my Structural Reinforcement rules for it since I worked on this before your reply and my HR on APEP rounds that brings them more in line with the ammunition modifiers in High-Tech and they only increase cost by 7, not 10 times.

Quite interesting. I did note some things on scale, though:

Quote:

The 110mm main gun does 7d◊8(3) pi++ dDamamge, and has range 17,000/130,000 with APEP or 3d◊11 pi++, range 8,600/65,000 with basic ball ammo. The cannon has ROF 1, ST 71M, bulk -13, rcl 3 and holds 133 rounds that weigh 53lbs each.
Is that RoF in Spaceship turns or in seconds?

Quote:

The two 15mm point defense railguns do 4d+2(2) pi dDamage, and range 100,000/250,000 with APEP or 2d+1(2) pi dDamage, range 50,000/130,000 with basic ball ammo. The guns have ROF 20, ST 49M, bulk -11, rcl 2, and holds 120 rounds per gun that weigh 30lbs each.
The 30lbs seems very high - at my first rough estimate, that's a length/width ratio of almost 150:1 for tungsten.

Quote:

They're probably not too far off though and as you can see, the ranges at a point they almost don't matter in ground combat.
Agreed; at that point it's either limited by terrain features or shooting tanks in the mountains a hundred kilometres distant.

The_Ryujin 04-14-2018 06:15 PM

Re: [Blog] n-Body Politics
 
Quote:

Originally Posted by kreios (Post 2171202)
Quite interesting. I did note some things on scale, though:

Is that RoF in Spaceship turns or in seconds?

Whoops, should of been more clear. Yeah, Spaceships 20sec scale. The tanks full mass would be almost all railgun if it fired at ROF 1 heh.

For some reason the point defense guns are in seconds though. Probably should of waited to get some sleep before stating this up heh.

Quote:

Originally Posted by kreios (Post 2171202)
The 30lbs seems very high - at my first rough estimate, that's a length/width ratio of almost 150:1 for tungsten.

Just ran the numbers again and I made a mistake. 30lbs is how much a round would weigh if it was a full sized medium battery, I forgot to reduce the weight for the round for being very rapid fire! It should weigh only 1.5lbs per shot.

If your interested:

Damage in d-scale from railguns is caliber in centimeters◊3. This takes into account that railguns have 2 miles/sec of muzzle velocity.

Caliber is 10^((SM+Gb)/13)
SM is the ships size.
Gb is 8 if a major battery, 7 if a medium battery, 6 if a secondary battery, 5 if a tertiary battery and 9 if a spinal battery.

Divide caliber by two if rapid fire, by 4 if very rapid fire.

Bullet weight is 10^((SM+Gw)/4)
SM is the ships size.
Gw is 12 if a major battery, 13 if a medium battery, 14 if a secondary battery, 15 if a tertiary battery and 11 if a spinal battery.

Divide weight by 5 if rapid fire, by 20 if very rapid fire (or by 4 and 16 if you want to be exact, oh David and your pentaphilia).

Number of shots is 10^((SM+Gs)/6)
SM is the ships size.
Gs is 6 if a major battery, 5 if a medium battery, 4 if a secondary battery, 3 if a tertiary battery and 7 if a spinal battery.

Multiply number of shots by 5 if rapid fire or by 20 if very rapid fire (or as before, 4 and 16).

Quote:

Originally Posted by kreios (Post 2171202)
Agreed; at that point it's either limited by terrain features or shooting tanks in the mountains a hundred kilometres distant.

Sir, they're counter firing!

Right. How much time until the round reach us?

19 minutes sir!

Very good. Plenty time for tea.


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