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Comment by sgt101 | Hacker News Reader

I looked into manned Mars missions in a fit of enthusiasm 30 years or so, and I concluded that we couldn't do it because landing a human + life support on Mars requires deceleration technology we just don't have. Basically the speed of a Martian orbiter needs to be reduced to 0 or so to avoid splatting the human, but Mars' atmosphere is so thin that parachutes just don't provide the required break.

Has that now changed or is it still just fantasy?

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Um, the moon also has no atmosphere. We were able to land on that in the 60's.

https://en.wikipedia.org/wiki/VTVL.

Lots of things to be worried about for a Mars trip, landing probably isn't really one of them.

But the moon is 1/9th the mass of Mars (approx)

The moon has an average orbital velocity of 1km per sec (approx)

Mars is 24km per sec (approx) Terminal velocity is 600ms, on earth it's 54ms

So we are talking about something that is an order of magnitude more difficult. I think if retro rockets are to be used then far more fuel will be needed. But that means far more mass, which means more fuel - how much fuel would be needed to slow something like Starship for example?

Many of the landers we've already put on Mars are heavier & less tolerant of G forces than a human, so it's clearly not an insurmountable hard limit. They use a combination of parachutes, retro rockets & airbags usually. But you're right that the lander stage has to be a small fraction of the size of the interplanetary stage, & the economics aren't very good. Maybe you'd need to send several Starships to Mars orbit to refuel & support a single one landing &/or returning to Earth -- at least until refueling facilities exist on the surface, & assuming Starship is actually capable of this mission.

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