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Old 08-20-2021, 03:46 AM   #1
fdsa1234567890
 
Join Date: May 2011
Default [Spaceships] getting into orbit without superscience?

The options don't seem great even at higher tech levels.

Chemical rockets obviously would still work, and with higher technology would at least be more affordable due to economic growth, but they would still be inefficient at best. While reusable designs would obviously help with costs, they are not really enough to really get truly serious numbers of people to into space in an economical fashion. Would these still have any real practical use at a higher TL?

HEDM would allow getting into orbit somewhat easily with an SSTO design, but they would also have a fairly high risk of explosion given the metastable nature of the fuel in use. I'm not sure how practical it would be for military applications considering this.

Orion drives would also work, but they also involve deliberately setting off nuclear weapons within the atmosphere, which make them extremely impractical as a common launch system. NTRs have a similar radiation flaw and are also no better than metallic hydrogen in terms of delta-v with even less thrust.

Are any of the higher tech fusion or antimatter designs even capable of getting to orbit in a practical design?
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Old 08-20-2021, 04:10 AM   #2
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Default Re: [Spaceships] getting into orbit without superscience?

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Originally Posted by fdsa1234567890 View Post
Orion drives would also work, but they also involve deliberately setting off nuclear weapons within the atmosphere, which make them extremely impractical as a common launch system. NTRs have a similar radiation flaw and are also no better than metallic hydrogen in terms of delta-v with even less thrust.
NTRs need not leak radioactive materials.

As for the overall question - yes, getting off Earth (and similar planets) with realistic rockets is a pain. Non-super science fusion is a no-go. Antimatter Thermal using high-thrust and/or water versions is workable at very high TLs, but isnt really any better than HEDM chemical rockets. On top of that, unless antimatter production is extremely cheap any antimatter rocket is going to cost an enormous amount to run. On the plus-side, antimatter-catalysed hydrogen (or water) fuel doesn't count as a volatile system.

There is another option from Spaceships 7 - the laser rocket. It gives the same performance as an HEDM rocket, but is cheaper and doesn't involve volatile fuel. The catch is that it depends on powerful laser systems at the launch facility, so it's not a low-infrastructure option. Also, the propellant is really cheap.
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Old 08-20-2021, 05:49 AM   #3
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Default Re: [Spaceships] getting into orbit without superscience?

I guess it all depends on how you define super science.

Since current scientific theory affirmatively declares FTL travel is not possible, anything allowing for FTL travel would be super science in my book.

But there are things that many scientists would not be surprised if they happened. So if you took a scientist 100 years into the future and we had FTL drives, that scientist would be surprised. One of the foundational theories he was taught as fact has been overturned in some way. This happens in the world of science. Newtonian mechanics were overturned by Einstein's relativistic mechanics. Scientists in Newtons day would be shocked by that. So even super science breakthroughs are not completely off the chart.

For me the next big scientific breakthrough that will change the very nature of space travel, and I expect it to happen at some point, is some sort of unified theory. Scientists are pursuing it right now. So while such an approach is "impossible" today, many think it is not forever out of reach. Unlike FTL drives. So I wouldn't call this super science. I'd call it speculative science for sure. We may never discover that theory. If we do though we can turn electrical power into gravitical thrust. We can probably bond new materials using strong and weak forces that we could never imagine creating now.

I suspect though that many would call the above super science because it is not yet possible. So your definition matters.
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Old 08-20-2021, 06:20 AM   #4
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Default Re: [Spaceships] getting into orbit without superscience?

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NTRs need not leak radioactive materials.
The important thing to keep in mind about NTR's is that it's the thermal bit that's crucial, it's just that said thermal energy is generated by a nuclear (fission) reactor. It should be possible to avoid making the exhaust radioactive at all, although I assume you'd lose some thrust in the mix (as you're essentially making more of the drive's mass consist of shielding). It's also possible that, even with radioactive exhaust, it's rather short-lived radiation, unlikely to cause any environmental issues. While the delta-V of NTR is decent (IIRC), I feel what makes it a real contender is the ram-rocket option, where the drive doesn't use any reaction mass so long as it's in an atmosphere above Trace. That lets you get (partially) up to speed at essentially zero cost, so you should be able to deliver a greater mass fraction into orbit. The big issue with NTR is what happens when you have a serious accident.

Quote:
Originally Posted by Rupert View Post
There is another option from Spaceships 7 - the laser rocket. It gives the same performance as an HEDM rocket, but is cheaper and doesn't involve volatile fuel. The catch is that it depends on powerful laser systems at the launch facility, so it's not a low-infrastructure option. Also, the propellant is really cheap.
As I've mentioned before, you can actually help justify the expense of the launch lasers in that they can readily double as defensive systems - if it's powerful and accurate enough to launch a spaceship into orbit, it can probably take out almost any ICBM over the same hemisphere. Of course, this also means you need the permission, or be powerful enough you don't have to ask for permission, of the other polities in the same hemisphere, as you could also readily shoot down any commercial flight or similar in that area.
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Old 08-20-2021, 06:54 AM   #5
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Default Re: [Spaceships] getting into orbit without superscience?

Space elevators are tricky to build and potentially dangerous if things go wrong, but do seem to be possible, and might end up being an efficient solution to the issue of getting into orbit, compared to rockets. There are also a few other methods of non-rocket spacelaunch that might work.

Atomic Rockets has a fairly long list of realistic Surface to Orbit concepts, both rocket (not limited to atomics) and otherwise.
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Old 08-20-2021, 07:07 AM   #6
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Default Re: [Spaceships] getting into orbit without superscience?

Realistically, getting into space by rocket is tough and inefficient.

If you’re working out the background for a future Earth, and want to figure out how to populate the solar system, then the answer to getting into orbit is… don’t use rockets.

https://en.wikipedia.org/wiki/Non-rocket_spacelaunch is pretty thorough, and should spark your imagination.
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Old 08-20-2021, 07:08 AM   #7
Fred Brackin
 
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Default Re: [Spaceships] getting into orbit without superscience?

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Originally Posted by fdsa1234567890 View Post
T

Orion drives would also work, ?
Orion drives "should" work but there's been no serious development done on them. Everything we think we know about them depends on some back of the envelope calculations. Some of these are 1960s vintage too and might not hold up that well these days.

There's trillions of $ in engineering work before they could fly even if there are no fundamental problems.

On the other hand I've heard that Gurps' assumptions about Nuclear Thermal Rockets are overly conservative in terms of thrust-to-weight. The radioactive exhaust problem is really only about traces of the fissionable core being transferred to the exhaust. This could probably be avoided with some sort of encapsulation system.
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Old 08-20-2021, 07:25 AM   #8
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Default Re: [Spaceships] getting into orbit without superscience?

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The radioactive exhaust problem is really only about traces of the fissionable core being transferred to the exhaust. This could probably be avoided with some sort of encapsulation system.
I had always assumed the radioactive exhaust was a form of secondary radiation - bits of your fission core flaking off seems like a really bad design, so it makes more sense if you're actually looking at the exhaust being made radioactive thanks to neutron bombardment. The way to avoid that would be more shielding for the reactor.
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Old 08-20-2021, 07:32 AM   #9
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I - makes more sense if you're actually looking at the exhaust being made radioactive thanks to neutron bombardment.
Only the exhaust is hydrogen or maybe water. Bombarding those with neutrons causes no serious radiation problems.

If you're using hydrogen (and you want to use hydrogen for the Isp) the most you can get is tritium when one of your neutrons hits a deuteron (i in 7000 of hydrogen atoms).
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Old 08-20-2021, 07:53 AM   #10
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Default Re: [Spaceships] getting into orbit without superscience?

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Originally Posted by Fred Brackin View Post
Only the exhaust is hydrogen or maybe water. Bombarding those with neutrons causes no serious radiation problems.

If you're using hydrogen (and you want to use hydrogen for the Isp) the most you can get is tritium when one of your neutrons hits a deuteron (i in 7000 of hydrogen atoms).
If you're in atmosphere, even if you aren't using a ram-rocket design I think your exhaust would contain free neutrons, which would interact with the atmosphere to generate secondary radiation. I'd still count that as "radioactive exhaust" - although I'll admit when I'm thinking of NTR in atmosphere, I'm generally thinking of a ram-rocket (and outside of atmosphere, the radiation hazard of the exhaust probably doesn't matter - it's primarily an environmental concern, after all). Although maybe those free neutrons were what you were talking about when you said "traces of the fissionable core?"

EDIT: Of course, I could be wrong and the intent actually is that flakes of the fissionable core are somehow getting into the exhaust. That just strikes me as a monumentally poor design. Of course, looking through SS1, I see no indications that any of the drives have radioactive exhaust, so I assume that information is in a different book?
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