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Comment by ddbeck | Hacker News Reader

One of the reasons for the skycrane is that it minimizes the area of the Martian surface that will be disturbed by the landing rockets. The skycrane approach moves less surface soil around the landing site (decreasing travel distance to pristine subjects for geological study) and deposits less rocket exhaust (which complicates chemical and biological studies).

NASA has an excellent and free ebook, _When Biospheres Collide_ [1], which goes into great detail about the problems posed by biological contamination (both forward and back). The book dedicates a long chapter to the great lengths taken with the Viking landers to avoid contamination problems. Having read it, I'm not at all surprised NASA is giving alternatives a try.

[1]: http://www.nasa.gov/connect/ebooks/when_biospheres_collide_d...

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Why didn't Viking worry about disturbing the landing site?

Also If it can drive why does it matter what happens to the landing site?

The Viking program was resigned to regarding the surface soil as untrustworthy for at least some (if not all) of their experiments. To get around this, the landers' robotic arms dug a few inches into the Martian surface to reach uncontaminated soil.

As for driving, the other commenters have it right: Curiosity isn't particularly fast and it's nice to start the scientific experiments sooner, rather than later. Moreover, driving around consumes limited electrical power which has to be shared with all the other systems on board, including transmitters and scientific instruments. Every minute spent moving from place to place is a minute of reduced data collection.

They drive at mm/s speeds. Moving over a few meters because the soil is stirred up is a huge waste of energy and time, not to mention the risk of failure.

No, not for curiosity. That robot is expected to drive many kms as part of its planned activities. Its nominal speed is 30 m per hour.

Which is 120 mm/sec -- about 4.75 inches, as parent noted.

Actually, 30 m/hour is 8 mm/sec. But that's a bad choice of units, because seconds is not a good mission time scale.

The point is that, within a couple of hours, you can drive beyond the contamination radius. And, over the span of the mission, you most certainly will.

Correct. Not sure where my math went bad.

The specific dust factor that is mentioned in the EDL video is dust, kicked up in descent, settling on the instruments within the robot.

Do you have a reference to the contamination rationale playing a role for the choice of a crane for MSL? Because I have not heard that mentioned.

Sorry, I wasn't able to figure out where I first heard about the contamination concern with MSL. I think I may have heard it in a video interview, which makes it nigh unsearchable. That said, a search of nasa.gov reveals several mentions of the use of a skycrane to reduce rocket exhaust contamination in relation to other missions, particularly ExoMars.

Hmm, if it's a factor for ExoMars, maybe it is for MSL too. Thanks for the info.

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