Now, here’s a picture many of you have probably already seen: the Mars Curiosity rover’s landing module under canopy on its way to the surface of the Red Planet, shot by the Mars Reconnaisaance Orbiter, orbiting 211 miles higher above it. (The original shot is available here and the whole release is here).
Parachutes work just the same in Mars as on Earth — in principle. But in practice, engineers have to deal with some otherworldly facts to successfully deliver a payload the the Martian surface.
Because NASA has successfully landed other craft on Mars (the two Mars Exploration Rover missions, Pathfinder and Viking).The later chutes have depended on Pathfinder’s design, just scaled up for heavier loads.
But in Mars’s thin air, even an enormous chute can’t decelerate a massive payload enough to protect delicate scientific instruments (or, for future reference, human beings). How do you keep the Frammis Spectrometer, say, from winding up as a pile of glass and carbon fiber in a smoking hole? The Spirit and Opportunity rovers’ landing craft used airbags, which protected the whole lander and only deflated when it was finished bouncing. The MSL instead uses a complex four-stage guided-entry landing architecture:
- Guided Entry: small rocket thrusters steer the atmospheric entry vehicle in the thin outer atmosphere, aiming the lander towards a precise point.
- Parachute Descent: when the air is thick enough, the parachute deploys and decelerates the entry capsule, within the parameters possible in the low-pressure Martian “air”. This part of the descent does not seem to be steered, but is at the mercy of the winds.
- Powered Descent: The capsule is a computer-controlled rocket-powered aircraft that flies on the powered lift of four main thrusters. It flies a precision approach to a selected sort of landing place (the exact area can’t quite be pinpointed… there are no GPS satellites orbiting Mars, so more complex and less precise methods than terrestrial Satnav must be used.
- When Powered Descent has brought the craft in position… then the “Sky Crane,” as they call it. essentially hovers and lowers the craft on a tether, bringing it to a gentle touchdown, before flying off to a separate landing. (It’s not clear if its landing place becomes a second scientific station, or if it’s completely expendable). The Sky Crane is new on this mission. The most recent Mars landers and rovers have relied on airbags to protect them from high-apeed landings.
Curiosity, the mobile part of a lander known by NASA as the Mars Science Laboratory (NASA has a deep and venerable culture of three-letter acronyms, so MSL), is about the size and weight of an old M151 Jeep, the favorite conveyance of SOG guys on a 3-day pass for snatching an NVA. One difference is the lack of the driver; another is that Curiosity is unlikely to be pilfered from some leg unit, painted black to conceal its illegitimate provenance, and turned to a higher purpose.
Unless. Unless the Martians have SF.