[X] My Assistant

[Guest_BruceMoomaw_*]

(1) The Jan. 2005 "Geochemical News" ( http://geochemsoc.org/archives/gn/gn122.pdf , pg. 9-16) contains an interview with David Des Marais full of intriguing statements of his views on both Mars exploration in particular, and the difficulties of interpreting possible Precambrian fossil evidence in general.

(2) MEPAG's Mars Human Precursor Science Steering group -- which issued its report in mid-2005 -- had a subgroup devoted to determining the necessary measurements to allow safe landings and surface exploration by both unmanned and manned craft, and its report is at http://sirius.bu.edu/withers/pppp/original...resentation.ppt . It's particularly interesting for two reasons. First it summarizes the kinds of measurements that must be made by the atmosphere-oriented 2013 Mars Science and Telecom Orbiter for such purposes -- the biggest problem is wind measurements at various altitudes, which may require development of a Doppler lidar. Second, page 8 indicates that the MER landings were even a nearer thing than we thought:

"Spirit designed with range of atmospheric states for during EDL

• A week before entry TES observation of dust storm changed anticipated
atmosphere

• Based on TES, a new density vs altitude profile was created

• However, the reconstructed atmosphere, done post-flight, indicated a
significantly different density (reduced by 15% between 20-30 km) from TES
calculation, and was very close to the limit of system performance

• Also, steadily increasing oscillations of both Spirit and Opportunity before
parachute deployment nearly exceeded safe range (could get tangled chute).

• Oscillations due to either unexpected atmospheric turbulence (some unknown
aerodynamic instability) or mechanical instability of vehicle in fluid.

• Lesson: The atmospheric state is not well quantified, with both models and
NRT calculations yielding weather predictions with large intrinsic errors

• Lack of atmosphere information may affect vehicle design, possibly creating
unstable descent system

• There are still unexpected turbulent layers, and unexpected affects from large
atmospheric dust storms"
_____________________________

Obviously, we cannot keep running these risks as our landers get bigger and more expensive -- a better understanding of Martian atmospheric behavior and changes is crucial for the immediate future, not just the moderate future.

[djellison]

Also very interesting to this thread.....

Mars Exploration Rover Entry Descent and Landing Trajectory Analysis
http://techreports.larc.nasa.gov/ltrs/PDF/...a-2004-5092.pdf

Mars Exploration Rover Terminal Descent Mission Modelling and Simulation
http://techreports.larc.nasa.gov/ltrs/PDF/...4-14sfmm-br.pdf

Doug

[The Messenger]

Also very interesting to this thread.....

Mars Exploration Rover Entry Descent and Landing Trajectory Analysis
http://techreports.larc.nasa.gov/ltrs/PDF/...a-2004-5092.pdf

From this report:

"The reconstruction work is ongoing in order to gain a better understanding
of what transpired during the “Spirit” and “Opportunity” landings."

I have been wondering out loud if and when this reconstruction would be completed, and I got an answer, of sorts, from Paul Withers. Paul has submitted a detailed paper to Icarus on the atmospheric reconstructs from the MER descents, and he hopes that it will be published within six months. Unfortunately, since some of the initial EDL parameters have not been publicly released (Do to ITAR???), Paul was forced to make a number of assumptions that limit the accuracy of his assessment. He also stated that the accelerometers and other instruments used for engineering, but not scientific, purposes will not be included in the PDL. (GRRRR)

The good news is, he also plans to release the software he wrote/used to create the model, so we may have another toy to play with. (I wonder if it will let me tweak the Mars gravity and MoI the way I think they need to be

Paul's paper has words to the effect that NASA has spent a lot less time and effort trying to create a complete MER EDL profiles than prior missions, and that a complete workup is not likely in the future. This also contrasted with these other reports. Clearly much more must be understood before a manned flight could ever be attempted, and for heavens sake, let's make sure the next probe has enough sensors to give us definitive answers without resorting to lame assertions of gross parachute over/under performance. (We saw this in the Pathfinder & Viking EDL's.)