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enter image description here

I'm becoming interested in how Mars missions are planning their landings. One aspect I see brought up time and again is Mars' awkward atmosphere - 'just enough there that you have to care about it'. This picture claims (I cannot vouch for it's validity) that Olympus Mons essentially pokes out of Mars' atmosphere.

Could an unmanned ship have a slow descent onto such a structure? Is it viable to roll down the mountain from there? Wikipedia says it is a 5 degree descent - hardly noticeable (though very noticeable in the picture above...)

I'm sure this has been ruled out for good reasons, I'm just curious what they are.

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    $\begingroup$ Why does your illustration show that Mauna Kea is higher than Mt. Everest? And I think that most of the mass of the Martian atmosphere is above Olympus Mons. Air density seems to increase rapidly already at ten times its height. But note the logarithmic scale and lets hear the experts, I cannot answer you, aerodynamics is a really difficult subject. $\endgroup$ – LocalFluff Nov 26 '14 at 16:44
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    $\begingroup$ They are trying to show that the ocean floor to the top of Mauna Kea is higher than sea level to the top of Mount Everest. Not necessarily a great comparison, but there is a point there that measuring from sea level is somewhat arbitrary. $\endgroup$ – Mark Adler Nov 26 '14 at 16:49
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    $\begingroup$ The Olympus Mons shown greatly exaggerates the slopes. The slopes of the flanks of Olympus Mons are around 5°. If you were there, you would hardly know that you were on the side of the largest mountain on Mars, especially since on a normal dust level day, you wouldn't be able to see the summit until you were most of the way up. $\endgroup$ – Mark Adler Nov 26 '14 at 16:51
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    $\begingroup$ I apologize for the inaccuracies of the image posted - it is not my creation. It was just the image that sparked this idea in my head. $\endgroup$ – Wutnaut Nov 26 '14 at 16:58
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    $\begingroup$ Taking off from Olympus Mons for a return trip would be a viable idea. But in that case, we're talking about a 550 km trip uphill. $\endgroup$ – MSalters Nov 27 '14 at 12:11
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Sure, with enough rockets and propellant you could land there. However the mass required for all that propellant would vastly reduce the mass of your payload, for an equivalent Earth launch mass.

Mars Science Laboratory was still going about Mach 17 (in Martian terms 1 Mach ~ 240m/s) when it was at the altitude of the top of Olympus Mons. So we're talking a lot of propellant. A very rough calculation assuming a storable biprop system would leave you with 1/4 to 1/5 of the payload you would have at "normal" landing altitudes, with the same entry mass.

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  • $\begingroup$ +1 and much better than my mobile-written post (concrete numbers cited). $\endgroup$ – Deer Hunter Nov 26 '14 at 19:32
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The real problem with Martian mountains is that by landing high you forego the ability to shed at least several hundred meters per second off your re-entry velocity available in the denser atmosphere below. Thus, you are forced to build in larger EDL (entry, descent and landing) propellant reserves and, all other variables equal, forget about putting more instruments into the lander.

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    $\begingroup$ But isn't less atmosphere an improvement? It is often popularly claimed that the Martian atmosphere is the worst thing to land in, too thick for this and too thin for that. So wouldn't the thinner atmosphere down to Olympus Mons improve this somewhat? That's how I interpret the question anyway. $\endgroup$ – LocalFluff Nov 26 '14 at 18:04
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    $\begingroup$ No, not high enough. You still have to go through the maximum heat pulse before you get to the altitude of Olympus Mons, but you have not shed much velocity yet. It's the worse of both worlds. $\endgroup$ – Mark Adler Nov 26 '14 at 19:20
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    $\begingroup$ Atmosphere is a plus for landing. The lower 27 km of Mars atmosphere can shed about 4 km/s. This aerobraking cuts needed propellent mass by more than half. It is taking off where an atmosphere is a pain. A maglev up the slopes of Olympus Mons is an interesting idea. It might provide enough velocity to rendezvous with the foot of a Phobos tether. $\endgroup$ – HopDavid Nov 27 '14 at 16:14
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The rovers we have exploring Mars move very slow. Every movement is planned on Earth based on analysis of the terrain. Even curiosity, the most capable rover ever built, will never go all that far from its landing point. Until we have rovers capable of independent movement over long distances rovers will be landed where they need to be to perform science. If good science can be done on Olympus Mons maybe they'll land one there, but given the distances involved they won't land there to avoid having to deal with the atmosphere.

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I believe a 5 degree slope would be easily within the limits of a landing system. From what I am reading the Apollo Landing Module had a slope tolerance of about 12 degrees. I found a chart in this document(page 11) which graphs the slope at landing sites for several Apollo missions. It seems to imply that many landing sites had rather high slopes, between 5-10 degrees.

Of course this was on The Moon with a gravity of 0.1654g, where as Mars has a gravity of 0.376g, which makes it a difficult direct comparison. There is also no atmosphere to consider on the moon.

I think that the wind on mars would pose a much larger problem than a 5 degree slope. Any landing system would have to be stable enough not to get blown over if it got caught in a storm, a requirement that would likely make any system have to be far more stable than concern of 5 degree slope at the landing site.

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NASA choozes missions at "science per dollar" basis. At mission development science definition team sets "points" for different scientific themes and studies how many points different mission designs and landing sites can give (versus cost and safety).

Other questions deal with difficulties of landing at high altitudes on Mars because of rarified atmosphere. In my opinion Olympus Mons also is not the most interesting area in terms of science. Olympus Mons is shield volcano so its surface should have low diversity - mostly volcanic rocks. No sedimentary rocks (clays, gipsum, etc), no history of hydrospre of Mars in past, no sites where possible lifeforms exist or could exist in past.

Also we don't need to land martian volcano to study igneous volcanic rocks and history of volcanism on Mars. Curiosity rover found igneous volcanic rocks in sand of martian dunes.

TLDR: Olympus Mons not very interesting area in terms of science.

Valles Marineris maybe much more promising because of geologic layers diversity. The main problems: landing ellipse should be diminished significantly, terrain can be too rough for landing, slopes of the canion can be too steep.

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