Caption to a picture of Viking at http://pds.jpl.nasa.gov/planets/welcome/viking.htm :

"Captured here in this rendering is a Viking lander just before it touched down on the Martian surface. The parachute and upper aeroshell can be seen in the upper left corner of the image. At this stage of the descent, the lander's terminal descent propulsion system (three retro-engines) had slowed the craft down so that velocity at landing was about of 2 mps (7 mph). Seconds after the lander reached the surface it began transmitting images back to the orbiter for relay to Earth."

With part of an airbag obstructing the main egress, and especially with the risks of 'bouncedown' ("in the lap of the gods" as Gary put it), I'm back to wondering again about the relative merits of 'bouncedown' vs. touchdown a la Viking.

My understanding was that Pathfinder was designed for FBC, and, airbags being cheaper than automated retrorocket descent, they were used instead. On the other hand, MPL was also part of FBC, and used retros - so I'm a bit confused. What determines the choice of one system over the other?

The Vikings showed how large interplanetary labs could be safely landed, completely automatically, with 70s technology. Isn't retro landing the only long-term option - not just re the anxiety of 'bouncedown', but especially the soft-landing requirements of larger infrastructure such as is needed in Mars Direct. (how are we going to hard-bounce an entire hab?)

The funding for MER is some US$800m. I can't find an equivalent figure for Viking but apparently it was worth $4 bil in 1995 terms. So, is cost savings still the main factor determining airbags for MER? or is it also the culling of the 'old engineers' (and the loss of their heritage) by Goldin et al? Both these factors could explain the loss of MPL. But, even given sufficient funding and skill, I guess I'm asking - is one landing system intrinsically more reliable than the other?

Any comments welcome ..
Daniel