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Is it possible for a compressed gas thruster to be used to launch a spacecraft into orbit?

Let's say, it's already moving at 250MPH(111.7 meters/second) relative to the planets surface. Planets surface has 90% of Earth gravity. Launch vehicle is 50km above the surface.

Lastly, let's assume that bthe compressed gas in question is CO2, and it's temperature is at least 65C before compression.

Also, would it be possible to design a re-usable space plane, capable of delivering one tonne of CO2 to a larger craft in a low orbit, then returning again? Using a compressed gas thruster?

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It would not be feasible. Compressed-gas thrusters have a very low specific impulse (a measure of fuel efficiency), and the ratio of launch mass to payload mass goes up exponentially with lower specific impulse. Achieving the horizontal speed needed for orbit is much harder than just gaining altitude, so the 50km start isn’t enough to make it work. One ton of compressed CO2 could in theory accelerate something like 45 grams to orbital speed, but that 45 grams has to include everything that isn’t propellant, including the tank that holds the pressurized gas — clearly not possible.

I assume you’re thinking about balloon launch from Venus. If you can arrange to bring some hydrogen with you, you could presumably make methane and LOX, which could fuel a powerful and efficient engine.

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  • $\begingroup$ I am thinking of something like a plane that flys around Venus on solar power, collecting CO2 and storing it in a tank. Then, once enough is collected, it launches itself into space, docks with a tanker-like spacecraft, and that spacecraft could bring hundreds of tonnes of CO2 somewhere else, where it is useful. Ideally, there should be a way to do this without bringing any resources from elsewhere. Is there any known material on Venus, or in it's atmosphere that could be used to propel a spacecraft into a low orbit? $\endgroup$
    – mzs.112000
    Jul 7, 2019 at 18:32
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    $\begingroup$ You could electrolyse carbon dioxide to carbon monoxide and oxygen. With enough stages that might get you to orbit $\endgroup$
    – Steve Linton
    Jul 7, 2019 at 22:11
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    $\begingroup$ at about 270s CO/O shouldn't need too many stages, but it's much more suited to Mars. $\endgroup$
    – user20636
    Jul 8, 2019 at 12:27
  • $\begingroup$ You could probably make hydrogen from sulfuric acid which is available on Venus in form of rain $\endgroup$
    – alexeykuzmin0
    Jul 9, 2019 at 17:56
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As the other answer says, flying to orbit on compressed CO2 is right out. Forget that approach.

However, if you are willing to use the CO2 as propellant in a nuclear thermal reactor, that has at least been looked at and found plausible for Mars applications, so maybe it could work at Venus.

Carbon Dioxide is the most readily accessible of all the candidate martian propellants. Composing 95% of the atmosphere, it can be obtained by pumping the martian air into a tank. At a typical martian temperature of 233 K, carbon dioxide liquifies under a pressure of 10 bars. Under these conditions, assuming an isothermal compression process, liquid CO2 can be manufactured for an energy cost of just 84 kW-hrs per metric ton. The NIMF engine produces over a thousand MW (thermal). If an electrical capacity of 1 MWe is built in as well, then the (2800 K, 40 MT) NIMF would be able to fuel itself for a flight into a high orbit in less than 14 hours! Liquid CO2 has a density 1.16 times that of water and is eminently storable under martian conditions.

(NIMF stands for Nuclear rocket using Indigenous Martian Fuel, dreadful acronym)

NIMF appears to have been conceived as a NERVA-like engine in which a nuclear reactor produces thrust by heating a propellant. Significant changes had to be made to use CO2 as the propellant.

The paper is here.

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