The Planetary Society Blog
By Emily Lakdawalla
Update on the Mars Science Laboratory site selection process
May. 14, 2007 | 10:04 PDT | 17:04 UTC
Mars Science Laboratory is repeating a highly successful process performed for the Mars Exploration Rovers, in which the entire scientific community -- not just the mission's science team -- has been offered the opportunity to provide input into the selection of the landing site. This process is being led by researchers John Grant and Matt Golombek, who are both quite committed to the idea that such openness yields better missions and better science.
They held their first open meeting here in Pasadena a year ago (which I unfortunately couldn't attend because I was at my 10th college reunion), and they've just announced the date for the second meeting, October 23-25. In their announcement of the second meeting, they mentioned a couple of interesting tidbits about the changes to the mission: "Please note there are a number of important changes to the engineering constraints since the first workshop that include a decrease in the latitude range and altitude to between ±45° latitude and below 1 kilometer MOLA-derived elevation, respectively." There's a document detailing the engineering constraints for the landing, updated on April 27, at the MARSOWEB website at NASA Ames. Here's the summary of those constraints, table 3.3 from this document:
| Engineering Parameter | Requirement | Notes |
|---|
| Latitude | 45°N to 45°S | | | Elevation | < +1 km | MOLA-derived elevation | | Landing ellipse radius | < 10 km | Excluding uncontrolled wind effects during parachute descent | | Slopes | 2 to 5 km length scale | < 3 degrees | Radar altimetry errors to start powered descent | | 200 to 500 m length scale | < 5 degrees | Control authority and fuel consumption during powered descent | | 20 to 40 m length scale | < 15 degrees | Control authority and fuel consumption during sky crane | | 2 to 5 m length scale | < 15 degrees | Rover landing stability and trafficability in loose granular material | | Rock height | < 0.55 m | Probability that a rock higher than 0.55 m occurs in a random sampled area of 4 m2 should be less than 0.25%.
Suggests low to moderate rock abundance | | Radar reflectivity | Ka band reflective | Adequate Ka band radar backscatter cross-section (> -20 dB and < 10 dB) | | Load bearing surface | Not dominated by dust | Thermal inertia > 100 J m-2 s-0.5 K-1 and albedo < 0.25; radar reflectivity > 0.01 for load bearing bulk density | | Surface winds | < 15 m/s (steady)
< 30 m/s (gusts) | Constraints apply over all seasons and times of day, at 1 m above the surface. Steady winds never exceed 40 m/s. |
I'm not actually sure what the old requirements were, but it sounds like the engineers are getting a little more conservative with their estimate of how their entry, descent, and landing (often abbreviated "EDL") system can perform. Requiring lower elevations usually results from the engineers wanting the EDL system to have more atmosphere for the heat shield and parachute to use to slow down the descent before they switch over to the final part of the landing system, which, for Mars Science Laboratory, is a new one called "Sky Crane."
I'll be following this process very closely, mostly because I can; I had a lot of fun watching the Mars community come to a consensus on the rovers' landing sites, and I think it will be just as enjoyable a process to watch for Mars Science Laboratory. In fact, I think it will be more fun, because this new rover will be more capable than Spirit and Opportunity, its landing system can get it to more rugged landscapes, and we'll have much better imagery of potential landing sites from Mars Reconnaissance Orbiter HiRISE and CRISM to use for choosing the future landing site. If you'd like to follow along, too, here's some good places to find the most up-to-date information:
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