Landing on Mars

Landing on Mars is a difficult problem.

To date over 60% of the missions [to the Martian surface] have failed. The scientists and engineers of these undertakings use phrases like "Six Minutes of Terror," and "The Great Galactic Ghoul" to illustrate their experiences, evidence of the anxiety that's evoked by sending a robotic spacecraft to Mars — even among those who have devoted their careers to the task. But mention sending a human mission to land on the Red Planet, with payloads several factors larger than an unmanned spacecraft and the trepidation among that same group grows even larger. If we need a four hundred foot diameter parachute manufactured in space out of aluminum oxide fiber and sent to Mars in stiff deployed condition instead of being packed, we will not learn about it unless we see a need to experiment. Such a parachute might merit investigation. It would avoid opening shock and might be sufficiently heat resistant to maintain structural integrity during the entire descent in Mars' low gravity well. The larger the diameter of the parachute, the less the max g loading. So let us be honest with ourselves about all necessary colonization technology.

The expected max temperature for ballistic entry into Mars atmosphere is expected to be a thousand or more Kelvin degrees above the melting point of aluminum oxide so coating course aluminum oxide fibers with potassium oxide which decomposes at 490 Centigrade might protect the fibers through atmospheric entry by ablative cooling or it might not. A mixture of potassium and sodium oxides as a coating or Teflon as a coating are things that are conceivable. Engineers in this specialty would have a better idea.

Another alternative with a greater probability of working, but possibly high cost, is a delta winged entry vehicle or lifting body with insulation like that on the space shuttle. The insulation would be somewhat cheaper because Mars atmospheric entry is less demanding than Earth reentry. It would fly supersonic close to the ground then ignite its rockets for landing. Then it would perform a Pugachev's Cobra maneuver loosing most of its horizontal velocity by drag and loosing the rest by rocket thrust. It would touch down on its tail.

Another alternative is the Sky Crane:

the 2009 Mars Science Laboratory (MSL) rover, weighing 775 kilograms (versus MER at 175.4 kilograms each) requires an entirely new landing architecture. Too massive for airbags, the small-car sized rover will use a landing system dubbed the Sky Crane. "Even though some people laugh when they first see it, my personal view is that the Sky Crane is actually the most elegant system we've come up with yet, and the simplest," said Manning. MSL will use a combination of a rocket-guided entry with a heat shield, a parachute, then thrusters to slow the vehicle even more, followed by a crane-like system that lowers the rover on a cable for a soft landing directly on its wheels. Depending on the success of the Sky Crane with MSL, it's likely that this system can be scaled for larger payloads, but probably not the size needed to land humans on Mars. (See Ref #1)