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Mars Rover Opportunity Still Stuck In a Dune
Maddog Batty writes "The mars rover Opportunity, which has been stuck in a sand dune since the end of April, is still going nowhere after wheel spinning attempts were made to free the probe. It did manage to move a very short distance as can be seen in the difference between these two images. Before this attempt the NASA JPL team were playing in their own sandpit trying to replicate the conditions on Mars. (older coverage)"
This is the first attempt to get out since it got stuck. Maybe I should have pointed this out in the article...
wot no sig
According to JPL's site the latest move was not an attempt to *free* the rover.
"Opportunity rotated its wheels on sol 463 for the first time since the rover dug itself into a sand dune more than two weeks earlier. The wheels made about two and a half rotations, as commanded, and the results were a good match for what was expected from tests on Earth. In the loose footing, the rover advanced 2.8 centimeters (1.1 inch) forward, 4.8 millimeters (0.19 inch) sideways and 4.6 millimeters (0.18 inch) downward. After further analysis of the results, the rover team will decide whether to repeat the same careful movement again on sol 465."
... and furthermore
The rover managers have successfully tested methods for extracting Opportunity from the sand. Principal investigator Steve Squyres has said all along that it will be a slow process:
http://athena.cornell.edu/news/mubss/
Opportunity didn't move for two weeks because JPL is being properly conservative and haven't tried until they understood the situation. The first small movement command was given on May 14, and Opportunity moved about the way they expected.
o rtunityAll.html#sol464
http://marsrovers.jpl.nasa.gov/mission/status_opp
The drive that you are seeing in these images that supposedly did not get the rover out of the dune is in reality a short test drive performed on Sol 463. The response from the rover was roughly what was expected by the MER engineers as you can read on the JPL site.
Considering that the wheels spun the equivalent of a 60 meter drive when they got stuck in the first place. (according to Dr. Albert Haldemann, Deputy Project Scientist for MER) they anticipate a fair amount of driving/spinning to get out. Also obviously if thier testing at JPL was wrong they did not want to worsen the situation to the point of no return on thier first try.
They have a plan.
The rover got stuck because they are driving over a series of long ridges in the sand. These ridges are in rows that run mostly along one direction. The rover was originally expecting these ridges to be solid and it drove straight perpendicular across them. Unfortunately they are not as solid so it got stuck.
Once they get the rover un-stuck, they will instruct it to move parallel to the ridges, and to weave in between them when possible to make forward progress. It will be slow, but it should minimize the chances of getting stuck again.
Put her in low gear. Don't accelerate hard. Just keep your foot off the gas. Let her ride slowly out of the rut. Once you've move a little bit, turn the wheel, gently, then keep moving a little. Eventually you get yourself out of the rut and back rollin' again.
Movies at wohba.com... http://wohba.com/2005/05/diggin-out.html
--- gr8s-n-ppppp
the sand is likely VERY fine sand, and fine sands have a tendency to behave much like fluids.
That's an excellent question, and the short answer is, we don't know. We crossed about 4km of this stuff uneventfully before we encountered the current dune (BTW, it's technically a ripple, not a dune), and we aren't completely sure what makes this one different from the rest.
I've been a little out of the loop, since I switched back to Spirit a few weeks before the Ripple Event, but I followed some of the email traffic as best I could. Last I saw, the working hypothesis was something to this effect: this ripple just happened to be a little taller and steeper than normal, and we just happened to be gaining a little elevation anyway (so we were at a greater tilt than normal) when we came across it.
I don't think there are yet any particular guidelines about avoiding them, but as you might expect, there's a team working on it.
The two basic possible explanations seem to be geometry (which I touched on above) and material. Someone threw out the idea that we can tell "dangerous" ripples from the regular kind by their albedo -- possibly, hazardous (fluffy) ripples are made of lighter dust and are therefore brighter. But I don't know whether that idea gained any traction. To my eyes, the ripple we're on didn't look particularly brighter than many others we've crossed without incident, but I didn't do any systematic analysis, so I can't really say.
My impression is that geometry is the leading candidate explanation, and if that proves to be the case, our guidelines will likely include evaluating every sol's traverse path for hazardous geometry. If we can't tell the rover how to avoid them itself, it might also mean no more autonav drives (where we let the rover find its own way), which would significantly slow our progress. But then, so would getting into another of these ripples.
This is all still a work in progress, though. Just remember, this is why we call it "exploration"!
``Life results from the non-random survival of randomly varying replicators.'' -- Richard Dawkins