Legs, Bags, or Wheels?
When choosing landing gear for Mars spacecraft, engineers have to weigh their options-literally.
- By Tony Reichhardt
- Air & Space magazine, August 2007
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At first the JPLers weren’t convinced a Skycrane-style landing, which looks precarious, would be controllable. But they watched videos of helicopters nimbly moving around large construction equipment, invited a Skycrane pilot to sit in on one of their engineering review boards, and of course did lots of ground testing to verify that the MSL system will work. As a bonus, the touchdown will be gentler: The rover’s wheels will hit the ground at a mere three feet per second, compared to eight feet per second for the Phoenix landing.
If the Skycrane maneuver works, it may become the landing technique of choice as NASA sends even heavier spacecraft to Mars. But that doesn’t necessarily mean the end of airbags. The engineers behind Europe’s ExoMars mission, due to launch in 2013, are leaning toward using a new kind of “vented” donut-shaped airbag that recently performed well in ground tests in Italy. The Spirit-size ExoMars rover would be ensconced in the middle, and the donut would plop down on the surface like a beanbag, then instantly deflate.
Even though vented airbags are an old idea, as with many technologies for exploring Mars, they haven’t yet been tried. And when it comes to the make-or-break landing system, spacecraft engineers don’t like to take chances. From the time the spacecraft enters the atmosphere to the moment of touchdown, a Mars landing takes just a few minutes. There’s often no redundancy in the hardware, and with TV cameras in the control room, there’s no place for mission managers to hide if things go wrong. Wish them all luck.