The current plans of Spacex is to have Starship get refueled in LEO and then fly to Mars and refuel it there on the ground. Will Starship also have to get refuel while it is in orbit around Mars on it's return trip?
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asked Aug 20, 2022 at 13:06
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$\begingroup$ @Jasen Nice pun, but: So far all the hype was substantially justified, against all odds, except for the timeline. $\endgroup$– Peter - Reinstate MonicaCommented Aug 21, 2022 at 10:14
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Mars has lower gravity and a smaller radius which significantly reduces the delta-v to reach orbit. Given that, and possibly also a lighter cargo load, Earth return can be done with only surface refueling.
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4$\begingroup$ As Elon Musk puts it, Earth is kind of a worst-case scenario for getting to orbit: high gravity and thick atmosphere. Most other bodies in the solar system are much, much easier. Mars' gravity is about one third of Earth's and its atmosphere only one hundredth. You can easily SSTO from Mars with lots of delta-v to spare to get to Earth. $\endgroup$ Commented Aug 20, 2022 at 16:29
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6$\begingroup$ @JörgWMittag I suppose musk has never heard of Venus then $\endgroup$– TopcodeCommented Aug 21, 2022 at 2:16
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2$\begingroup$ @Topcode Or Jupiter. Or of the 1000 km/h storms on Saturn. "The weather forecast indicates that a launch today is unlikely. Everybody back into the bunkers." $\endgroup$ Commented Aug 21, 2022 at 10:09
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4$\begingroup$ Or the sun. I thought it was pretty clear he was limiting things to the planets one could conceivably be launching a spacecraft from the surface of. Of those, Venus is the only one that even has a surface. $\endgroup$ Commented Aug 21, 2022 at 16:53
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1$\begingroup$ It's not really about surface gravity or radius. Low surface gravity reduces the thrust required to lift off and the gravity losses in ascent, but even on Earth gravity losses are a small fraction of the overall delta-v requirements. What you really want to look at is escape velocity, which for Mars is 5 km/s, compared to 11 km/s for Earth. $\endgroup$ Commented Aug 21, 2022 at 17:02