[Spaceships] Winged Spaceships

[Anthony]

Originally Posted by scc

From what I understand Jet engines are supposed to help in cases like this

The short answer to that is 'not at TL 8, and only maybe at higher tech levels'. Regular jets have a maximum atmospheric velocity that's only 15-20% of the delta-V required for orbit, and there are quite substantial costs to adding a jet engine.

Originally Posted by scc

If I switch to a X15-B inspired design things get a little better, but part of my problem is that one of the worlds I'm working with has a higher escape velocity then Earth

Then use HEDM rockets, nuclear-thermal, or laser launch; conventional rockets are hopeless.

[jeff_wilson]

Originally Posted by scc

From what I understand the problem comes from trying to use the reactor to power the engines. Basically you can build a plane that has enough lift to carry a reactor, you can't build a reactor that can generate enough power to make the plane fly

This is not correct to my knowledge, it can be done in principle, but it's very expensive and risky to try *and* the ICBM was invented so the chief need for a round-the-world-unrefueled bomber evaporated.

You might not get a very fast plane, though.

[scc]

Originally Posted by Anthony

The short answer to that is 'not at TL 8, and only maybe at higher tech levels'. Regular jets have a maximum atmospheric velocity that's only 15-20% of the delta-V required for orbit, and there are quite substantial costs to adding a jet engine.

Yes, but those jet engines reduce the amount of work rockets need to do by the same percentage, while also increasing the efficiency of the rockets due to the higher altitude light-off. And the settings at TL 9, or where you talking IRL?

Originally Posted by Anthony

Then use HEDM rockets, nuclear-thermal, or laser launch; conventional rockets are hopeless.

HDM works, maybe too well. 8 tanks is 4.8 mps, not enough even with jet assist, but 9 is 6.3 too much (In one case enough to reach escape velocity)

[RyanW]

Originally Posted by jeff_wilson

This is not correct to my knowledge, it can be done in principle, but it's very expensive and risky to try *and* the ICBM was invented so the chief need for a round-the-world-unrefueled bomber evaporated.

And even though ICBMs can't do everything a B-52 can do (it's not that great for tactical carpet bombing, for example), aerial refueling, plus the fact that the US Air Force expects to have access to Diego Garcia, Incirlik, and Kadena, have eroded the need further.

[Anthony]

Originally Posted by scc

Yes, but those jet engines reduce the amount of work rockets need to do by the same percentage, while also increasing the efficiency of the rockets due to the higher altitude light-off. And the settings at TL 9, or where you talking IRL?

Talking IRL -- the problem is that adding a jet engine and wings to a huge cost (both weight and money), so you aren't going to do it on a SSTO, and if you're doing it with a multi-stage to orbit you need a rocket that is transportable and launchable from a jet, without destroying the jet, and again, that's expensive in design terms (normally, multi-stage rockets separate stages in vacuum and are willing to expend lower stages. That's not a realistic option for a jet). It's basically one of those things that sounds like a good idea in theory, but has trouble in practice.

Originally Posted by scc

HDM works, maybe too well. 8 tanks is 4.8 mps, not enough even with jet assist, but 9 is 6.3 too much (In one case enough to reach escape velocity)

There's a wide variety of HEDM fuels in the literature, and the stuff in Spaceships is at the high end; you can plausibly set delta-V to some lower value. Practical SSTO probably requires on the order of 0.25-0.3 mps/tank.

[scc]

I was talking about boosters, but some of my points may apply to SSTO's.

Flyback ability, a booster can land at a facility allowing it to be recovered, jet engines even allow for margins of error. This is opposed to it soft landing somewhere inconvenient or being lost all together, the later costing millions in lost spacecraft.

Being able to obey noise restrictions. This may not sound like much, but as the jet engines are quieter housing may be built closer to the spaceport, which will support a small city and having the workers legally require an hour + drive every morning will cut into you costs (Unions won't allow this to come out of leisure time). Plus it is possible that your 'spaceport' is just a normal airport with longer runway's, much cheaper then building everything from scrath

[RyanW]

One option currently being pursued is the combined-cycle engine, that can function as jet engines in atmosphere, and as rockets in space (or at speeds of Mach 6+).

Quick math suggests a tank of H2 would give 17 times the operational duration of a tank of H2/LOX when operating in air breathing mode. However, that is probably a completely wrong way to figure it. Even ignoring the differences of aerodynamic operation, the engine would run as sort of hybrid of a chemical rocket and a thermal rocket (using H2/O2 reaction to heat N2 reaction mass).

[Anthony]

Originally Posted by RyanW

Quick math suggests a tank of H2 would give 17 times the operational duration of a tank of H2/LOX when operating in air breathing mode. However, that is probably a completely wrong way to figure it.

9 times (the oxygen mass is 8x the hydrogen mass, not 17x), but yes, it's a completely wrong way to figure it, because the incoming airstream is moving. It's still a huge benefit at low velocities -- if you can overcome the engineering challenge of designing an engine to work on two totally different types of fuel, and the oxygen intake systems, and the wings if you use them.

Originally Posted by scc

I was talking about boosters, but some of my points may apply to SSTO's.

Flyback ability, a booster can land at a facility allowing it to be recovered, jet engines even allow for margins of error. This is opposed to it soft landing somewhere inconvenient or being lost all together, the later costing millions in lost spacecraft.

Oh, no, those potential advantages are obvious. It's just that the design compromises required to take advantage of those advantages have, thus far, not made this a practical design.

[vicky_molokh]

Reconfigurable systems might be the closest thing SS has to a switchable-modes engine. Raises some TL questions, of course.

[ericbsmith]

Originally Posted by vicky_molokh

Reconfigurable systems might be the closest thing SS has to a switchable-modes engine. Raises some TL questions, of course.

While Reconfigurable Systems may be TL 11 or ^, realistically any system where the two modes are closely related (such as propulsion systems that use the same or similar fuel in a similar manner) should probably be only one TL higher than the standard systems are.