Lowest altitude viable Mars orbit

Is it possible to be in Mars orbit and collide with Olympus Mons?

(Explorer8939) writes:

Is it possible to be in Mars orbit and collide with Olympus Mons?

No. The summit of Olympus Mons is about 27 km above datum. The scale height
of the martian atmosphere is about 11.1 km, and the pressure at "datum" is
61 millibars, so the pressure at the summit is about 0.5 millibars, which
corresponds to the pressure (and density) at an altitude of only 55 km
on Earth --- barely out of the stratosphere, and well below the exosphere.
Hence, the atnospheric density at the top of Olympus mons is far too high
for a stable orbit.

For a second reality check, google on "mars atmospheric entry," and quickly
learn that peak heating for the Mars Pathfinder probe occurred at around
40 km above datum, and that the Mars Climate Orbiter burned up because
the english-versus-metric screwup meant that it had a closest approach
of about 57 km above datum instead of the planned 145 km above datum.


-- Gordon D. Pusch

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"Explorer8939" wrote in message
om...
Is it possible to be in Mars orbit and collide with Olympus Mons?

It's possible to be in Mars orbit and scrape the bottom of the Valles
Marineris if your perigee is low enough. Once, anyway 8-)

Jonathan Wilson

In article ,
Explorer8939 wrote:
Is it possible to be in Mars orbit and collide with Olympus Mons?

No, alas. (Not that anyone would want to collide with it, but an orbit
passing low over it would be quite the tourist ride...) Aerobraking and
reentry altitudes on Mars are actually similar to those on Earth -- the
atmosphere is much thinner, but the weaker gravitational field means
density drops off rather less rapidly with altitude. And Olympus Mons is
high, but it's not *that* high...
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

"Explorer8939" wrote in message om...

Is it possible to be in Mars orbit and collide with Olympus Mons?

Doubt it. It's 27km high and there are dry ice clouds up as high as
50km. http://www.daviddarling.info/images/...tmosphere1.jpg


--
__ "A good leader knows when it's best to ignore the __
('__` screams for help and focus on the bigger picture." '__`)
//6(6; ©OOL mmiv :^)^\\
`\_-/ http://home.t-online.de/home/ulrich....lmann/redbaron \-_/'

I wrote:

[...] the pressure at "datum" is
61 millibars, so the pressure at the summit is about 0.5 millibars,
^^^^^^^^^^^^^^

Typo correction: The above should read "6.1 millibars," not "61 millibars."


-- Gordon D. Pusch

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Henry Spencer wrote:
In article ,
Explorer8939 wrote:
Is it possible to be in Mars orbit and collide with Olympus Mons?

No, alas. (Not that anyone would want to collide with it, but an orbit
passing low over it would be quite the tourist ride...) Aerobraking and
reentry altitudes on Mars are actually similar to those on Earth -- the
atmosphere is much thinner, but the weaker gravitational field means
density drops off rather less rapidly with altitude. And Olympus Mons is
high, but it's not *that* high...

But if you are doing touristy things on Mars, you could aerobrake to near it
then start a retrofire and fly past it on the other side to retrograde orbit.

--
Sander

+++ Out of cheese error +++

Henry Spencer wrote:
In article ,
Explorer8939 wrote:

Is it possible to be in Mars orbit and collide with Olympus Mons?


No, alas. (Not that anyone would want to collide with it, but an orbit
passing low over it would be quite the tourist ride...) Aerobraking and
reentry altitudes on Mars are actually similar to those on Earth -- the
atmosphere is much thinner, but the weaker gravitational field means
density drops off rather less rapidly with altitude. And Olympus Mons is
high, but it's not *that* high...

My remembrance of Martian aerobraking guidance studies in the late
1980's (single pass) was that we were using periapsis altitudes less
than the height of Mt. Olympus. That would depend on the mission of
course, and the atmospheric models have presumably been upgraded since
then.

- Matt

Managed to dig out a conference paper:
AIAA 87-2401, "Optimal Guidance for Future Space Applications,"
J.E.Bradt, M.V.Jessick, J.W.Hardtla. AIAA GN&C Conference 1987

The last example trajectory is a Martian aerocapture patterned
after the Mars Sample Return Mission studies of the day.
Periapsis altitude was 80000 ft, a bit less than 25km.
L/D 0.75 and 141 lbf/ft**2 ballistic coefficient

T writes:

Explorer8939 wrote:

Is it possible to be in Mars orbit and collide with Olympus Mons?

Without yet reading the other (probably more informed) replies

That is generally a mistake.


I'll say if you can sustain a Powered Orbit (counteracting the tendency
of a fast orbit speed leading to a greater orbit circumference)

I think you need to review your basic orbital mechanics. The lower an
orbiting body is, the faster that orbiting body moves.


then you can skim right over the top of the highest peak you choose.

The real problem is friction from the martian atmosphere. So unless you
want to consider hovering flight under rocket power a "powered orbit,"
IMO, your answer is incorrect.


-- Gordon D. Pusch

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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.