Douglas said:

"It seems a little overly complex in places - the deadbeat airbags seem like a recipe for a nightmare - but I'd like to hear Gary's words on the entry design and how it compares to the B2 design (page 13),

Unsure on the nano-rover design, looks like it would have to be teathered, and getting out past the collapsed airbags wont be easy.

BUT - if ESA is going to do Mars landings, I think something like this is a far better place to start than going straight into ExoMars.

Now - let the character assasination and lambasting begin"

--- end quote ---

I'll start with the character assassination: IMHO anyone who funds a proposal with Colin Pillinger's name on it is courting disaster. If I was the funding authority reading this proposal, my immediate response would be to reject it with the admonition to get rid of Pillinger. After they got Pillinger out of the picture, they should resubmit the proposal for actual technical review.

Concerning the aeroshell design: Somebody is learning! I'm pleasantly surprised. The design is a hybrid between the basic Viking geometry and Huygens. The half angle is correct. The ballistic coefficient is conservative. They didn't specify the nose radius which was amateurish (nose radius is a crucial parameter). From the drawing it looks like the nose radius might be too small (it should be half the base radius). They used the Huygens design philosophy of a large forebody having a sharp outer radius lip with a smaller radius backshell. This was done to keep the ballistic coefficient small and the backshell deep inside the wake bubble where gas temperature is cooler. I'm a little bit nervous about forebody heatshields having a sharp outer radius edge like that. That sharp edge will tend to get very hot (probably hotter than the stagnation point). The sharp edge will also have dynamic pressure issues that could cause TPS material spallation. Another worry is a strong vortex will form in that pocket between the back of the forebody and the backshell. Vortices behind a supersonic vehicle are never steady and tend to expand and contract. Strong vortex oscillations can make the vehicle statically unstable at a higher Mach number. This is a classic example of the design trade-off: One would like to make the ballistic coefficient as large as possible (the design as-is does that nicely). However one would also like a nice clean shape with no concavities that permit vortex formation.

Aeroshell design conclusion: This Mars 2009 aeroshell design is superior to the Beagle-2 design and appears to be practical. Someone has obviously learned from their mistakes.

Doug was critical of the air bag design but I would disagree. Whoever advised them about the aeroshell also gave them good advice about the airbags. Unlike Pathfinder and MER, Mars 2009 is not using decellerator rockets. This means it will hit the martian surface at a much higher speed. Mars 2009 can take that approach because it is a much smaller vehicle that derives benefit from the laws of scale. However that higher impact speed requires the designer to be extra clever about their airbag design. Having something that bounces like MER and Pathfinder is not an option. The airbag needs to pop on the initial impact. Having multiple cells means multiple pops which allows better kinetic energy dissipation. A viable proposal would have to include signficant research and development funding for this new airbag design.

Bottom line: Overall this design looks practical. If they can get rid of Colin Pillinger then they may have something that can actually work on the surface of Mars.

Gary