[Spaceships] How should a large station... duck?
 

Say that a trans-to-post-human culture decides to implement one more kind of backup of itself, in the form of a complex ecology intended to last for ridiculously long periods with minimal nudging, inside a SM+34 McKendree Cylinder habitat. (Call it about a million square km of surface area, mass around 10 quadrillion tons; something vaguely like https://www.orionsarm.com/im_store/CYLINDER2.jpg , though with much larger solar collectors. And we can handwave construction methods with the magic words "von neumann".) And let's say that physics allows for spacecraft to accelerate to goodly fractions of lightspeed.

Without drifting too close or far from its home star, how can the cylinder's orbit be jogged, to make it more difficult for a hostile near-c interstellar impactor to target the cylinder?

Eg, can solar sails (or some other propulsion without reaction mass, such as a magsail) be arranged so the cylinder can 'tack' along its orbit, sometimes going a bit prograde and sometimes retrograde (or radial and antiradial, or normal and antinormal), so its average orbit remains at the right distance? Should I dive into the orbits of Janus and Epimethus, and have two cylinders who can "trade orbits"?

Would it help if the star this cylinder orbits was deep enough in a nebula to make it infeasible to pick out the cylinder from afar?

I'm hoping to find some numbers that add up to let the large cylinder be sufficiently unpredictable to dodge any good-sized near-c impactor before that impactor can change course. I'd rather stick with Reality Classic, but am willing to posit a reactionless drive (within certain limits). If that doesn't work out, I'm willing to shrink the cylinder to the point where such manoeuvres become possible, though I'd still like it to be large enough to be a BDO with lots of interior space to be explored. If /that/ doesn't work out, I'm willing to consider alternate approaches, such as Large Numbers of smaller habitats (eg, https://orionsarm.com/im_store/JenkinsDysonSwarm.jpg ), though I'd have to significantly re-jigger my intended narrative, so it's a last resort.

How many tricks am I missing?


-----8<-----

Preliminary build:

* SM +34, USL. TL10, no superscience
* SM +34, USL. TL10, no superscience
- 10 Quadrillion tons, length 1M yards (cylinder: length 914 km, circumference 1106 km, radius 176 km, diameter 352 km), dST/HP 150M, Hnd -10/5
* Design Features:
- Spin Gravity (0.2G, $100 Quintillion, -2 to handling)
- Self Healing (TL10): heals 1.5M HP/day, $200Quintillion
- Stealth Hull (-8 to detect): $1Quadrillion
- Chameleon Hull (-4 to see): $700T
* Design Switches:
- Exposed Radiators
- Slower Industrial Systems
- Pyramid 34: Armor Volume (9 armor systems: dDR * 1.4)
* Systems (18 + 2 core):
8 * Armor, Stone: dDR 30,000 (30k * 8 * 1.4 = dDR 336,000, semi-ablative: every 10 points of damage removes 1 point of DR)
1 * Armor, Nanocomposite: 500k dDR, $50Qn (500k * 1.8 = 700,000, total dDR 1,036,000, avg dDR 345,333 each for fore/central/aft)
10 * Open Space: each 500M areas (each 25M acres, total 250M acres, max of ~200M humans using traditional farming), Total Automation (replace 300M workspaces, $1.5Quintillion), $200T
1 * Smaller systems: 30 SM+31 systems (or even more smaller ones):
- SM+31 Cargo Hold: 15Qd tons
- SM+31 Control Room: C20, Comm/sensor 30, 15360 control stations, Total Automation (replace 30B workspaces with $150Qd), $600Qd. -1 to Handling/Stability.
- SM+31 Enhanced Sensor Array: Array Level 32, Total Automation (replace 30B workspaces with $300Qd), $600Qd
- SM+25 Robofac or Vatfac: $15T/day, Total Automation (replace 30M workspaces with $150T), $30Qd
- SM+25 Habitat: 2B cabins, Total Automation (replace 30M technicians with $150T), $300T
- SM+20 Hangar Bay (for robotic miner ships): capacity 1B tons (max SM+16, door diameter 700 yards), launch 3125k tons/minute, Total Automation (replace 3M workspaces with $15T), $3T
- SM+25 Mining: 1.5B tons/day, Total Automation (replace 30M workspaces with $150T), $300T
- SM+25 Refinery: 5B tons/day, Total Automation (replace 30M workspaces with $150T), $300T
- SM+25 Power Plant, Reactor, Fusion: 1PP, 400 years, Total Automation (replace 30M workspaces with $150T), $1.5Qd (refuel $150T/400y, ~= $375B/y)
- SM+25 Solar Power Array: 1PP, $1.5Qd
- SM+19 Robot Arm: Total Automation (replace 30k workspaces with $150B), $3T
- SM+18 Weapons battery, Hidden: 1B * SM+9 Weapons, Major Battery (TL10 UV Laser: 4dx5 damage, range L, fixed mount). $22.5Qd. (333M can be aimed at any one target)
- SM+14 Weapons Battery, Hidden, $22.5T: 1B * Missile launcher, 20cm: sAcc -2, range L, rcl 1: SM+5, 7 shots ea
- Ammunition, 1T shots: 200M tons, $200T
- Ammunition, 1T shots, 100 kt nuclear: 200M tons, $300T

* Price so far: $366.71 Quintillion.

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Re: [Spaceships] How should a large station... duck?
 

I don't see any sensors listed. If you're depending on naked eye sightings of the impactors, it's going to be pretty close to the habitat already. Depending on how close to lightspeed the impactor is, you may be taking about a minute between sighting the impactor and the collision, which won't let you change your velocity by much, so it'll depend on how big the impactor is both absolutely and relative to the habitat.

You can probably slow the habitat down or speed it up enough to generate a miss for a 5-mile diameter impactor aimed at the very end of the habitat, OTOH, if the impactor is targeting the habitat dead amidships, you probably aren't going to be missed, and a 5 mile diameter impactor, even at the speed of most objects in our own solar system would be an extinction level event for Earth. I don't see the habitat faring better. And on the gripping hand, unless your hostiles strap their own Captain Kong onto the impactor with a steering mechanism, they're going to have a hard time targeting an orbiting planet much less a habitat.

Re: [Spaceships] How should a large station... duck?
 

Buried in the small stuff: SM+31 Enhanced Sensor Array: Array Level 32, good enough to auto-detect a SM-10 piece of space junk at 50,000 miles, or a SM+15 rock at 7 AU.

(Also potentially relevant: Self-healing at 1.5M HP per day. So a typical SM+15 rock of 3M tons would typically do 630,000 dDMG on impact, 284,667 dDMG after armour, not enough to disable a full-sized system, and healed right up in four and a half hours.)


I'm trying to work out a threat profile starting from, say, 100 light-years away. Some posthuman culture gets hints that the cylinder backup project exists, decides to change that, and launches some relativistic impactor to nip the thing in the bud, before it even gets to be ten thousand years old. A few launch-lasers powered by the local solar-power Dyson Swarm sends the thing on its way, and they forget about it to focus on their most recent internal fight about which software license is the One True Way. A bit over a century later, the impactor has tried to nudge its course to give it the best chance of hitting its target, and we open up with only a light-month or so left to go... how well will the impactor have jiggled its target point by this point? How much more jiggling can it still do, and how well can it see its target to know where to aim, and how far has the target moved from its earlier estimates? ... and so on.

Re: [Spaceships] How should a large station... duck?
 

Can you give it a heavy counterweight that it releases? Or have it break into two or more pieces? That should give it a quick jump out of the way, but it's one-use only, and it would take some time and effort to reset.

Re: [Spaceships] How should a large station... duck?
 

It needs to change its' movement in an unpredicatable fashion with a frequency that is shorter than the amount of time impactors have to adjsut their courses.

So if that relativistic doomsday machine has to commit to one particular course a month befre impact change your orbit more often than that.

Re: [Spaceships] How should a large station... duck?
 

That was my thought. Use a spin tether and have the station either be in two halves or have a large counterweight. If it needs to move quickly you simply disconnect the tether and the two halves go flying off in opposite directions at high velocity.

Re: [Spaceships] How should a large station... duck?
 

Fair enough. Anyone up to sketching out one or two sample attacks, so I can get a better idea of the range of what to watch out for? :)


Mm. Tricky. My initial vision for this station is a can of pop, the size of Egypt if you rolled up that country into a tube. Sure, with advanced tech you could build in a line to split the thing in half when you wanted - but you'd lose all the important stuff inside if you did.

I'm already positing fairly strong nano-stringies just to keep a moderate level of gravity with the diameter in question. To convert the thing into a pair of sub-habitats, then the outer edge of their rotation would be the same as the outer circumference of the original cylinder, implying a much smaller overall hab.

Still, having a rock ready to release is basically the same as having a mass-driver engine installed; maybe I should take another look at having some emergency one-shot propulsion that uses up fuel. I suspect high-thrust is more important than overall delta-v, if the goal is just to jog the place out of the way of a large rock before it hits... but I'll have to dig through the SS books and run some numbers to be sure. :)

Re: [Spaceships] How should a large station... duck?
 

This is simple, in principle. The key question is how much delta-V can you generate at right angles to the impactor's trajectory, after you detect him?

If this is definitely more than he can generate in that time for changing his course to try to hit, by enough to cover the size of your cylinder and the impactor, you can force him to miss.

If you can't generate even enough to cover the sizes of the cylinder and the impactor, he'll hit if he was already on course to do so when you detected him.

If it's in between those values, it's a matter of life-or-death tactics in a brief period of time.

You do have an advantage in that relativistic time dilation operates to his disadvantage, both on his reaction time and on his thrust. However, he's going to be ready to react, and the cylinder won't be unless it has an automated defence system against this kind of threat, which is on-line all the time.

Re: [Spaceships] How should a large station... duck?
 

A SM+34 object would mass around 10 quadrillion tons, as mentioned above, and could not really afford to dodge anything. We assume that it possesses counter rotating sections that allow it to change orientation, but it is simply too massive to maneuver rapidly enough to dodge anything that can maneuver. A dumb relativistic object could be avoided through changing rotation rates to allow slight repositioning, assuming they received a few months warning.

A SM+34 object should really be more than a million square kilometers, as that suggests a mass of 10,000 tons per square meter column. Atmosphere masses 11 tons per square meter at sea level, meaning that the rest of the mass would need to be something else. A kilometer of water masses 1,100 tons per square meter and a kilometer of soil masses around 2,750 tons per square meter. You would either need an excessively thick ecosystem or a larger object to account for the mass.

So, if we examined a SM+34 object, a single habitat section would have sixty trillion cabins, and would require 1 trillion workers. If we assume high automation, we could reduce that to 100 billion workers. We could easily support giving every individual the equivalent of six cabins (one luxury cabin with total life support, one office, and one steerage cargo) and have the equivalent of six cabins worth of other things per person, allowing us to support five trillion people per habitat section.

An SM+34 habitat would probably have six habitats, six open spaces, three steel armor, and fifteen smaller systems (cargo holds, control rooms, fuel tanks, hanger bays, power plants, weapon batteries, etc.). It could support up to 30 trillion humans and could require around 1.5 trillion personnel with high automation. It would have dDR 100,000 with steel armor, meaning that it could ignore most attacks without any worry. Its SM+33 tertiary VRF laser weapons would have an output of 300 PJ and would deal 3d×5,000 (2) damage each hit, allowing it to turn most relativistic projectiles into plasma moving 0.9c in the opposite direction.

Re: [Spaceships] How should a large station... duck?
 

I feel like pointing out something obvious. If the enemy can pick out the cylinder from that kind of range, then the people who built the cylinder can definitely see the kind of energy expenditure it takes to accelerate a missile to relativistic speeds; something which would be much more obvious.

Re: [Spaceships] How should a large station... duck?
 

Well, a far enough starting point (like a light-year) and a slow enough acceleration (no more than 0.01g) might go undetected with the proper design, but it would be unlikely to get above 0.05c in a realistic setting. Anyway, destroying such a treasure would be beyond insanity, as it is a prize beyond compare. If it is a TL12 civilization, its productive capacity would be phenomenal (a SM+33 nanofactory could produce $3 quintillion worth of products per hour), and it could produce a SM+15 battleship every second with enough materials.

Re: [Spaceships] How should a large station... duck?
 

So far, for a one-shot emergency dodge system, the best option I've found so far is to use some of the smaller-than-SM+34 systems on a laser rocket. A SM+32 rocket, with total automation, costs $2.5 quintillion (not all that much on top of the $366 quintillion pricetag so far), requires an external source of a yottajoule of laserbeams (for which we can presume a small dyson swarm close to the star), and provides 0.2 gees of thrust (any more, and some of the interior will start falling upwards during maneuvers). A SM+33 fuel tank of ablative plastic costs $1 quintillion (plus $15 quadrillion for the fuel), and provides a delta-v of 0.15 miles/second (which, at 0.2 G, happens over about 2 minutes.

Ignoring orbital mechanics, with a diameter of 350 km, the station will diverge from its original course by its own width after about half an hour. I've already figured out that the cylinder's sensor array can auto-detect a SM+15 projectile 7 AU (or 58 light-minutes) away, and larger projectiles even further out... so we just might have a viable dodge system against simple near-c impactors.

Of course, more complicated attacks would require more complicated defenses, but I'm pleased that the numbers work out for at least the simplest case. :)

(Of course, after using this engine, the station would have to send out robo-miner craft to whatever other bodies in the solar system have the raw mass to refill the tanks, and the lasers might need to refill their capacitors, so it would be some time before a second course-change could be made, so a second impactor might be able to do what the first one didn't.)


I was mostly going by Spaceships' "Open Spaces" numbers; 10 SM+34 Open Spaces have that much surface area. ... I rather suspect that the SpaceShips system isn't quite designed for tin-can habs of this type, and so the scaling is probably off, but I don't have the math chops to go outside the books here.


The goal of this station is to keep a viable population of sapients living inside an ecosystem for arbitrarily long periods of time, even if those sapients happen to be stuck in the local version of the Stone Age for a few million years here and there. (They probably won't, with the occasional insertion of a vatfacced copy of one of the mind-uploaded builders every so often to check on things, but the goal is to be prepared even for that.) I'm generally assuming total automation is in place for every system.


... A fairly important point that I'd forgotten. :)


I've heard a few mentions that GURPS' sensor rules are a bit wonky, so I'm not on sure footing saying what can and can't be detected at interstellar ranges; which is why I'm focusing more on the cylinder's nearest light-month or so radius.


Beamriders. Gotta love 'em.


Even just a SM+29 TL10 Robofac (costing around 1% of the original station cost estimate), using the Slower Industrialization toggle, should be up to producing $1.5 quadrillion per day, which is nothing to sneeze at for anyone who can figure out how to gain control of the place. You'd only get one of those SM+15 battleships every 13h20m instead of per second, but really, how many of those do you need at a time? :)



Say, does the SpaceShips system include any mention of laser-boosted lightsails, outside of SS7's laser rockets that use ablative plastic?

Re: [Spaceships] How should a large station... duck?
 

SM+15 battleships are only a couple trillion, so I think you are low balling the production figures. Since the production figures in Spaceships 6 assumes daily rates rather than hourly rates, $3 quadrillion a day (nanofactories multiply by 20) equals 1,500 SM+15 battleships per day. The Star Forge has nothing on the level of production.

One of the odd things about such a station is that it could easily be mistaken as a metallic asteroid rubble pile when it is inactive due to its low density (it is the mass of a large asteroid like Euphrosyne 31). Without any anomalous energy readings, it might be ignored for decades or even centuries, as rubble piles are annoying to deal with, and its true nature might not be visible until someone goes to mine it. Heck, something like that could be floating in the Kuiper Belt and we would not know it until it went active.

Re: [Spaceships] How should a large station... duck?
 

The general case of dodging is that you have to move by more than the diameter of your object, in less time than the object has to correct.

This will usually not be possible for a competently designed impactor, as it will likely have as good course correction as the target, except in the extreme relativistic range, where light speed lag causes problems for both the defender and the attacker.

At 0.99c, in the reference frame of the target, it takes light 500s to cross 1 AU, and it takes the impactor 495s, so you have only 5s warning. This generally makes detection not very viable. However, the impactor has the same problem: you probably don't know the target's position with more accuracy than 'orbiting that planet', so if you've got 5 km/s delta-v available for course correction, you need to know the target's position something like 1,250s before impact, which means you need to be able to detect the target (and distinguish it from possible decoys) at 250AU.

Re: [Spaceships] How should a large station... duck?
 

What about using the robotic miners as tugs?

Re: [Spaceships] How should a large station... duck?
 

Place it in mutual orbit with a tethered counterweight. To dodge, reel out more tether.

Re: [Spaceships] How should a large station... duck?
 

I don't see the difficulty. The scaling of Spaceships that allows you to build a sM+34 object just by moving your decimal point far to the right will let you build an engine to propel it too.

Re: [Spaceships] How should a large station... duck?
 

That's very clever. I like it.

Re: [Spaceships] How should a large station... duck?
 

If you can manage a really big megastructure, you can one-up that by having a counterweight-and-cable system that wraps around the star and lets you adjust your orbital radius. Over lengthy projectile flight times that should let your orbital period be unpredictable so they basically have to search the entire orbit for you during the approach.

(If you don't mind being unsubtle, putting a big opaque cloud of satellite/statite objects around the system so the attacker can't see anything until they get very close is a possibility, but it sounds like security-through-obscurity is wanted here and being a blatant astronomical anomaly might hurt that.)

Re: [Spaceships] How should a large station... duck?
 

Put those things around the megastructure you're trying to hide. Then make the shielding items out of very transparent glass or plastic and fill them witha m ix of hydrogen with a little helium and maybe some traces of methane and/or ammonia.

From a few light years away you might look like a gas giant. :)

Re: [Spaceships] How should a large station... duck?
 

Scale issues. A SM+12 robo-miner/tug is around the size of one of the Pyramids; the station is around the size of the entirety of Egypt.


In case it might affect anyone's thought processes, I'm planning for the plot to be set a long time after this station was built, after several pre-industrial civilizations have risen and fallen internally. I want to heavily lean on the tropes of exploring the unknown, at several scales: not knowing what will be found inside the station, outside the station, and possibly even within the main characters if I can manage that level of subtlety. If I can get away with it, a more physics-compliant version of Dungeon Crawl Classics.

Re: [Spaceships] How should a large station... duck?
 

True, but I did note the was up to a billion tons of robo-miners, so if a large percentage could be used at once it might help (slowly). But equally there could be a number of reasons why it wouldn't work.

Re: [Spaceships] How should a large station... duck?
 

I think the problem is that as your orbital habitat gets bigger the distance that it has to move in order to dodge gets bigger, but the time you have to dodge in doesn't get any longer, so you need higher velocities and therefore greater acceleration. A habitat that is SM+34 is about a million metres across. If it gets, say, 100 seconds to dodge in it must apply 200 m/s² to dodging, which is about twenty gee. Whereas as ship of, say, SM+13 only needs to dodge by 300 metres in the same time: 0.006 gee is sufficient.

Give an SM+13 ship half a gee of acceleration to dodge with and then it can dodge in 11 seconds. An SM+34 habitat with half a gee needs 633 seconds.

It's an orbiting habitat the size of a minor planet, with no drives. With a bit of public-source intelligence it ought to be possible to predict its position for a year in advance with a precision better than one kilometre.