In Kerbal space program I built a mini cubesat (similar to NASA’s lunar flashlight probe) and managed to land on the moon only using ion thrusters. However, it was risky because it took a few tries. In the first couple of attempts the cubesat came down too fast. What other issues may appear if such a mission will happen in real life? Or what issues did appear if such a mission has happened?
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asked Jan 20, 2023 at 13:26
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13$\begingroup$ Do not conflate KSP with reality. $\endgroup$– David HammenCommented Jan 20, 2023 at 14:18
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$\begingroup$ All low-power engines in KSP are vastly overpowered because real world low power burns are simply too slow. Most of them also have vastly more Δv than they should so they can give reasonable burn times despite being overpowered. No, it's not reasonable to do a mission to Minmus and omit the ascent stage, but in the game you can reach orbit on the jetpack. $\endgroup$– Loren PechtelCommented Jan 20, 2023 at 23:21
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$\begingroup$ And, even more extreme, it's not reasonable to bring a Kerbal down from low Kerbin orbit just in a suit. (Requires level 3 Kerbal to have a parachute.) In the game if you burn the whole jetpack retrograde it reduces the thermal load on re-entry to just survivable. $\endgroup$– Loren PechtelCommented Jan 20, 2023 at 23:26
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$\begingroup$ different question but somewhat related Are patched conics (and by induction, KSP) "useless" for simulating ion propulsion? $\endgroup$– uhohCommented Jan 21, 2023 at 1:35
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1 Answer
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This is one of the cases where Kerbal Space Program differs significantly from real world rocketry.
The stock ion engine in KSP has a thrust of 2000 N at 250kg, a thrust-to-weight ratio of 4.9 on the Mün.
Real world ion engines are much much weaker than that. NSTAR (0.092 N at 8.33 kg) and NEXT (0.236 N at 13.5 kg). Thrust-to-weight ratios of 0.0068 and 0.011 on the Moon
So those game engines are unrealistic beasts, close to 3 magnitudes more powerful than the real deal, and thus capable of hoovering against their own weight. (which is an absolute requirement for a soft landing).
answered Jan 20, 2023 at 16:23
SE - stop firing the good guysSE - stop firing the good guys
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1$\begingroup$ So you are saying that a moon landing with an ion thruster is impossible with the currently available ones, because an ion thruster cannot produce enough thrust to even life itself off the surface of the moon? $\endgroup$ Commented Jan 20, 2023 at 16:54
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5$\begingroup$ Yes. There may be other problems too, but this is the main one. $\endgroup$ Commented Jan 20, 2023 at 16:56
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$\begingroup$ I will wait a day or so, but if no other answers come I will accept this one. $\endgroup$ Commented Jan 20, 2023 at 16:57
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$\begingroup$ Nobody is stopping you from trying your mission in RSS-RO with real engines and planet sizes. $\endgroup$– RAD6000Commented Jan 21, 2023 at 14:11
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$\begingroup$ It didn’t work with RSS-RO. Kept on coming down too fast $\endgroup$ Commented Jan 21, 2023 at 15:59