Lowest altitude viable Mars orbit

In article ,
Ben Hallert wrote:

Of possible interest, it is my understanding that because of gravity, the
Martian atmosphere extends further from the ground then Earths, so any long
term orbit would necessarily need to be higher to avoid significant drag.
400 kilometers might not be a good place to park your crew return vehicle,
for example, unless you were confident that it could be reliably reboosted
as needed.


On the flip side, how deep a hole would you have to dig on Mars so that
the atmospheric pressure at the bottom would approach 1 atmosphere? (And
how much thicker is the atmosphere at the bottom of Vallis Marineris
(say) than the "average" pressure on Mars?

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Ben Weiss | Any technology distinguishable from magic
President & CTO | is insufficiently advanced.
Shell & Slate Software | - Clarke C. Arthur

"Ben Weiss" wrote in message
...
In article ,
Ben Hallert wrote:

Of possible interest, it is my understanding that because of gravity,
the
Martian atmosphere extends further from the ground then Earths, so any
long
term orbit would necessarily need to be higher to avoid significant
drag.
400 kilometers might not be a good place to park your crew return
vehicle,
for example, unless you were confident that it could be reliably
reboosted
as needed.


On the flip side, how deep a hole would you have to dig on Mars so that
the atmospheric pressure at the bottom would approach 1 atmosphere?

Would tossing Phobos at Mars be enough to dig that hole?

Ben Weiss wrote in message ...
In article ,
Ben Hallert wrote:

On the flip side, how deep a hole would you have to dig on Mars so that
the atmospheric pressure at the bottom would approach 1 atmosphere? (And
how much thicker is the atmosphere at the bottom of Vallis Marineris
(say) than the "average" pressure on Mars?

http://www.madsci.org/posts/archives...5313.As.r.html

You'll find your answer...

Basically, even 10 km down, at the bottom of Valles Marineris, you'd
only have 50 millibars, that's 5% of Earth's pressure, and 6 times
less than at the top of Mount Everest.

Ben Weiss wrote:

On the flip side, how deep a hole would you have to dig on Mars so
that the atmospheric pressure at the bottom would approach 1
atmosphere? (And how much thicker is the atmosphere at the bottom of
Vallis Marineris (say) than the "average" pressure on Mars?

Average pressure on Mars is 7 millibars and we want 1000 millibars,
so the pit needs to be log-n(1000/7) = about 5 scale heights deep.
Scale height is 10.8 km on Mars; therefore the pit will need to be
roughly 54 km deep.


;K

Ben Weiss wrote:
In article ,
Ben Hallert wrote:

Of possible interest, it is my understanding that because of gravity, the
Martian atmosphere extends further from the ground then Earths, so any long
term orbit would necessarily need to be higher to avoid significant drag.
400 kilometers might not be a good place to park your crew return vehicle,
for example, unless you were confident that it could be reliably reboosted
as needed.


On the flip side, how deep a hole would you have to dig on Mars so that
the atmospheric pressure at the bottom would approach 1 atmosphere? (And
how much thicker is the atmosphere at the bottom of Vallis Marineris
(say) than the "average" pressure on Mars?


As a very, very, very rough guess, the scale height of the martian
atmosphere is going to be some 10Km.
The atmospheric pressure is 1% of earth, so you need 7 scale heights, to
hit 1 bar.
70Km.