[Spaceships] TL10 Space RV

[Ulzgoroth]

Originally Posted by Michael Thayne

The Vehicles sidebar ignores the fact that the earth's atmosphere isn't like an ocean, with a well-defined "top". Atmospheric pressure gradually decreases as you get higher and higher. This means that aircraft generally have a flight ceiling well below the altitude where it's possible to orbit for any length of time before de-orbiting (or even burning up) due to drag. The altitude record for an air-breathing aircraft is ~37 kilometers, less than half the commonly quoted "edge of space" of 100 km.

If you want launching from Earth's surface to be easy, I would recommend allowing fusion torches, standard/hot reactionless engines, and/or contragravity lifters. If you want space travel to be super-duper cheap I guess you could also arbitrarily declare that in your setting, those systems cost less than they do in RAW.

This is true, but it's eliding a key difference between air-breathing aircraft and this vessel:

The reactionless thruster produces the same 0.1g at all speeds and altitudes. That's the main limiter on real high-altitude airplane operation. Air-breathing engines lose performance (or outright stop working) in thin, fast airstreams. (Even if you're using a non-combustion air-breather like a nuclear ramjet.) No problem with that here.

Without that problem, I think things look good. Drag and lift both tend to scale with air density and the square of airspeed, AFAICT, so if you can get above the surface effect at sea level with 0.1g you should be able to sustain flight an any altitude with 0.1g, and that means you can insert into low orbit for sure.

[Michael Thayne]

Originally Posted by Ulzgoroth

Without that problem, I think things look good. Drag and lift both tend to scale with air density and the square of airspeed, AFAICT, so if you can get above the surface effect at sea level with 0.1g you should be able to sustain flight an any altitude with 0.1g, and that means you can insert into low orbit for sure.

<Does algebra>

Oh huh, you're right. At higher altitudes, you can cancel out having less lift due to lower pressure by going faster, which you can do because the lower pressure means less drag. So it al works out.

EDIT: This actually upends a lot of assumptions I and other seem to have historically made about world-building futuristic settings. Kinda wanna test out a low-thrust spaceplane concept in a simulator like Orbiter. But I'm going to resist the urge to get too deep into this in the near-future.

[AlexanderHowl]

Wouldn't gravity drag be an issue with only 0.1g acceleration? For a 3g acceleration, you end up losing around 0.5 km/s when attempting to reach orbital velocity (meaning gravity drag is around 0.15g). In effect, the spaceship should not be able to fly, much less leave the atmosphere, as gravity drag would negate its acceleration.

[Ulzgoroth]

Originally Posted by AlexanderHowl

Wouldn't gravity drag be an issue with only 0.1g acceleration? For a 3g acceleration, you end up losing around 0.5 km/s when attempting to reach orbital velocity (meaning gravity drag is around 0.15g). In effect, the spaceship should not be able to fly, much less leave the atmosphere, as gravity drag would negate its acceleration.

'Gravity drag' only exists when you're thrusting against gravity. You basically don't ever do that at all with this type of craft.

Gravity drag is also a somewhat misleading name, and describing it as an acceleration suggests you have in fact been mislead...