In article ,
lid says...

On 19-08-04 17:53 , Jeff Findley wrote:
In article ,
says...

On 2019-08-03 12:54, Jeff Findley wrote:
...
Even Musk's plan to use Starship to go to Mars will take a *lot* of
tanker Starship flights to LEO just to bring up enough propellant for

LEO is the keyword here. not "Gateway". LEO lets you deliver fuel much
faster, and with far less hot re-entry than coming back from Gateway.

The Starship tankers won't need to be able to handle a reentry from a
return from the moon and/or Mars. So their thermal protection system
might not need to be quite as complex/expensive. But, the crewed
Starships going to the moon and/or Mars will need to be able to handle
that.

A fall-back alternative might be for a Starship, returning to Earth from
Mars, to use its remaining fuel not for landing, but to brake into a low
orbit around Earth. A tanker could then refuel the Starship with enough
fuel for reentry and landing on Earth.

Orbital mechanics is a harsh mistress. The fact is the mass of heat
shields for reentry (i.e. aerodynamic braking) is *far* less than the
mass needed to do propulsive braking into the earth orbit.

However, braking into LEO from a Mars-return trajectoy may need
considerably more fuel than a mere landing on Earth after an aerobraking
re-entry, so this fall-back method would probably reduce payload
capacity; the question is by how much, and I suspect by a lot. This
could perhaps be solved by refueling the returning Starship in low Mars
orbit, after launch from Mars and before trans-Earth injection, using
tankers (or Starships acting as tankers) from Mars, but that is getting
a bit complex...

Refueling in Mars orbit might make a lot of sense if you expect to do
propulsive entry back into earth orbit. That Mars tanker could
presumably land back on Mars to be refilled again by the in-situ
propellant production equipment. But you'd have to "run the numbers" to
see if this even makes any sense.

Jeff
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