[Spaceships] getting into orbit without superscience?

[Prince Charon]

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.

[DemiBenson]

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.

[Fred Brackin]

Originally Posted by fdsa1234567890

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.

[Varyon]

Originally Posted by Fred Brackin

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.

[Fred Brackin]

Originally Posted by Varyon

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).

[Varyon]

Originally Posted by Fred Brackin

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?

[Fred Brackin]

Originally Posted by Varyon

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" - ?

Free neutrons don't constitute any sort of long-term radiation hazard. All of the major components of Earth's atmosphere are still harmless after absorbing a neutron. The neutron hitting a nucleus but not being absorbed does transfer some energy but it's pennyante stuff. You're in much more danger from the heat of the exhaust.

[Rupert]

Originally Posted by Varyon

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.

Actually, some designs would leak radiation - in the form of fuel. You see, having a barrier between the energy source (fuel) and the propellant limits how hot you can run the rocket to what that barrier can handle. So some designs relied on careful flow design to keep the fuel from (mostly) leaving. Better performance at the cost of radioactive exhaust and consuming expensive radioactives at a much higher rate.

[malloyd]

Originally Posted by Rupert

You see, having a barrier between the energy source (fuel) and the propellant limits how hot you can run the rocket to what that barrier can handle.

This is why *all* reaction engine designs have trouble getting into orbit. Chemical rockets already run hot enough containing the exhaust is an issue. So there's not a lot of space for going hotter (the requirement for better fuel efficiency), which combined with the issue that heating by something other than reaction in the fuel adds weight for both the heat source and heat exchange system, means there really isn't lots of room for improvement even in theory.

The truth is that even a lot of spacecraft engines and power plants that aren't "officially" superscience really are, it's just the required superscience is the somewhat invisible "requires parts that still work at temperatures too high for chemical bonds to exist".

[Anthony]

Originally Posted by malloyd

This is why *all* reaction engine designs have trouble getting into orbit. Chemical rockets already run hot enough containing the exhaust is an issue. So there's not a lot of space for going hotter.

Well, you can use hydrogen as reaction mass instead of combustion byproducts; that allows an ISp of around 1,400 without being any hotter than current rocket. The problem is that reactors can't generally run anywhere near as hot as a current rocket engine.