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dodecahedron
2008-Apr-27, 05:51 PM
Why did NASA choose to use chemical thrusters to slow the descent of the Phoenix lander rather than re-using the airbags used with the Mars Exploration Rover missions?

AGN Fuel
2008-Apr-27, 11:53 PM
Why did NASA choose to use chemical thrusters to slow the descent of the Phoenix lander rather than re-using the airbags used with the Mars Exploration Rover missions?

A few possible reasons spring to mind:

- The landing site is important, as this is not a 'rover' mission and so the lander can't relocate itself to a better position if it bounces on landing into an awkward spot.
- Again, because the lander must operate from where it lands, it must have clear access to the Martian soil beneath. The deflated airbags may risk interfering with that access.
- There are a number of sensitive instruments on board, that may not be able to survive the rigours of an impact landing.

These are my speculations only. The real reason may well be something completely different. :)

Van Rijn
2008-Apr-28, 12:23 AM
Why did NASA choose to use chemical thrusters to slow the descent of the Phoenix lander rather than re-using the airbags used with the Mars Exploration Rover missions?

This article has a fairly detailed discussion of the trade-offs and the reasoning for the choice:

http://www.airspacemag.com/space-exploration/mars_airbag_supplement.html?c=y&page=1

Apparently, airbags would be possible, but it was designed before they were verified to work. Also, there are weight tradeoffs, and a rocket landing allows for a more pinpoint (less random) landing location, as AGN Fuel discussed.