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NASA Selects Landing Site for Phoenix Mars Lander
Earlier this week, NASA made a course adjustment for its Phoenix Mars Lander which puts it on a path to land in "Green Valley" on the Red Planet late next month. The site was chosen for being a broad, flat expanse that is relatively free of rocks capable of damaging the lander when it sets down. The location will be confirmed pending further reconnaissance from an orbiting satellite. The probe's mission, which we've previously discussed, is to investigate subsurface ice.
"The landing area is an ellipse about 62 miles by about 12 miles (100 kilometers by 20 kilometers). Researchers have mapped more than five million rocks in and around that ellipse, each big enough to end the mission if hit by the spacecraft during landing. Knowing where to avoid the rockier areas, the team has selected a scientifically exciting target that also offers the best chances for the spacecraft to set itself down safely onto the Martian surface."
They do have a better way. Retro rockets to slow the descent to a crawl + springy legs because 1 to 2 m/s is still a hard landing. It comes down to cost. This solution is more expensive.
Bearded Dragon
Considering that Phoenix is a re-fly of the 1998 Mars Polar Lander mission, this was the subject of an intensive study of the command dictionary, flight software, and ground software.
Please remember that the 1998 MPL and MCO missions were part of NASA's "Better Faster Cheaper" movement. These were budget class missions that exchanged significantly increased risk, in the form of less internal and external oversight and review, for significantly lower cost. The problem is that landing on another planet is a very hard problem, especially Mars. This mission carried "flagship" mission difficulty (ala MER) but wasn't given the budget to address anywhere near all the higher order risks. Keep in mind the atmosphere on Mars is too thick to use retro rockets all the way to the ground, like on the Moon, and too thin to use parachutes all the way down, like we have done on Earth. Also keep in mind that MPL and Phoenix missions use a landing system which is closest to a system that we hadn't flown in over 20 years (Viking). And it was chosen primarily for budgetary not technical reasons. I'm not even going to get started with the landing radar...
The kinds of errors that killed MPL and MCO were exactly the kinds of risk that NASA bought by forcing the budget low. They purchased a mission with flagship risk on a budget that precluded mitigating those risks.
Phoenix is a three-quarter measure to fix the errors of MPL. It's a re-fly of the 1998 MPL mission with the kind of oversight and peer review that the original mission would have had if it were designated the kind of budget that it deserved. The results of these ongoing studies have led to numerous design changes in hardware, radar firmware and antenna design, flight software, and fault protection. The team at Lockheed and JPL is cautiously optimistic.
Phoenix is a re-fly of MPL using flight-spare MPL hardware. The difference is that since the spacecraft and instruments were already on the shelf, there was relatively more budget for the kind of investigation, review, and rework that the original mission should have had. As a result, we've identified and fixed a sobering number of fatal errors in the original design.
The disposition of the team at this time is "cautiously optimistic", which is more confidence than we had on MER at the same time. That said, there is always residual risk and the chance of just having a bad day.