[X] My Assistant

[Guest_Analyst_*]

It has been mentioned here several times that Spirits EDL has been on the edge of failure, that is was a close call. The vehicle was only one or two seconds away from failure.

Is there any evidence (links, papers) available in the public regarding this? Everything I have suggests EDL was within the typical expected uncertainties (3sigma) and the deployment timeline left enough time for an even later parachute deployment and all the subsequent events. Even without DIMES the impact velocity would not be above of the airbag design limits. There exactly has been this close call?

Analyst

PS: Sorry Doug, wrong forum. Please move to Spirit. Thanks.

[mcaplinger]

It has been mentioned here several times that Spirits EDL has been on the edge of failure, that is was a close call. The vehicle was only one or two seconds away from failure.

I might argue that even in the best of circumstances the MER EDL system is only "seconds away from failure" -- the margins are pretty tight.

Many MER close calls were described in http://pweb.ae.gatech.edu/people/rbraun/cl...-ugly-truth.pdf
but the one that seems like it fits the bill is "dust storm 10 days before Spirit landing reduces atmospheric density" -- http://sirius.bu.edu/aeronomy/withersmericarus2006.pdf has a lot of technical detail about the atmosphere's state. There was a timing parameter that could be adjusted by ground command to factor in the atmospheric density, and this was commanded shortly before EDL (see http://www.nasa.gov/offices/oce/llis/1480.html and http://www.nasa.gov/pdf/160654main_Mars%20...onsultation.pdf ) That alone would make anyone nervous, although I don't know what the sensitivity of this parameter really was. If Rob Manning drops by this forum again, obviously he would have some insight.

The story in ROVING MARS about DIMES saving the day is certainly based on fact, though the DIMES team understandably would like to believe that their work was critical. I don't think we know for sure what would have happened without DIMES.

[Mark Adler]

I don't think we know for sure what would have happened without DIMES.

Well, for one thing, Spirit would not have landed in Gusev. Without DIMES to counter the higher modeled winds at Gusev, we would not have been able to certify Gusev as a "safe enough" landing site. We would have instead landed at the "wind-safe" but potentially boring Elysium landing site.

Mark Adler