On Mar/18/2018 at 2:32 PM, Niklas Holsti wrote :
On 18-03-18 15:56 , Jeff Findley wrote:
In article ,
says...
** ...
In a "Pan Am flight 006 to Mars and back,* would the mass of the vehicle
making the drop from space and land to surface be roughly the same ? Or
would landing at one planet require much more fuel?

You'd need a lot more fuel and oxidizer to land on Mars since Mars
atmosphere is so thin you won't get anywhere near as much aerodynamic
braking as you get on earth.

Hmm. In his "Making Life Multiplanetary" address in September 2017, Musk
showed a simulation of a BFS Mars landing with text saying "over 99% of
energy removed aerodynamically". If less than 1% of the orbital energy
remains for rocket braking, is that really a significant difference
between Mars and Earth?


One percent of the energy of Mars' escape velocity (escape not
orbital energy, I think that is the relevant value to use here)
means one tenth its speed. That's about 503 m/s. According to
https://www.reddit.com/r/spacex/comm...tegy_analysed/
or https://tinyurl.com/hk252mj
the falcon 9 first stage inbound at 1.1 km travels at 105 m/s.
So 5 times the speed, 23 times the energy on Mars vs Earth.

I'd say it is significant but not a big problem. Of course, less
than 1% leaves plenty of room, 0.1% is less than 1%. But I would
think that it would be close to 1%, 5 times the speed seems
reasonable to me.


Alain Fournier