Winter Quarters, at Low Ridge Haven |
Winter Quarters, at Low Ridge Haven |
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#1
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Member ![]() ![]() ![]() Group: Members Posts: 166 Joined: 20-September 05 From: North Texas Member No.: 503 ![]() |
Since Spirit is no longer "Running for the Hills" and it appears that she will be staying at Low Ridge Haven for the next eight months or so, it seems like a good time to start a new topic.
I thought we could start with the great panorama stitched by jvandriel, and then altered by Tesheiner. We are going to become very familiar with this view in the coming months. David [attachment=5107:attachment] (286k) |
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#2
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![]() Senior Member ![]() ![]() ![]() ![]() Group: Moderator Posts: 2262 Joined: 9-February 04 From: Melbourne - Oz Member No.: 16 ![]() |
Very odd.
I see three possibilities: 1) They saw Michael Howards worry about MMB problems if too many image were taken at one site/drive number and decide to help out. ![]() 2) They 'tried' to move the broken wheel. 3) They refined there knowledge of Spirits position (there were a number of 'sun finds' at the time of the change) and defined a new site with the new values. I'm not sure I beleve any of these though, a question for Jim Bell I think... James -------------------- |
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#3
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Senior Member ![]() ![]() ![]() ![]() Group: Moderator Posts: 4279 Joined: 19-April 05 From: .br at .es Member No.: 253 ![]() |
Very odd. I see three possibilities: 1) They saw Michael Howards worry about MMB problems if too many image were taken at one site/drive number and decide to help out. ![]() 2) They 'tried' to move the broken wheel. 3) They refined there knowledge of Spirits position (there were a number of 'sun finds' at the time of the change) and defined a new site with the new values. I'm not sure I beleve any of these though, a question for Jim Bell I think... James Right on the money, James! From http://marsrovers.jpl.nasa.gov/mission/status.html: QUOTE SPIRIT UPDATE: Spirit Perfects Pointing Parameters, Collects Images Large and Small - sol 855-859, June 1, 2006:
Since arriving at the rover's current location on the 807th sol, or Martian day, of exploration (April 10, 2006), Spirit's knowledge of its attitude relative to the sun has drifted. The rover uses an onboard computer to keep track of attitude changes, but error builds up in this measurement over time. On sol 855 (May 30, 2006), rover planners transmitted an attitude update of 1.97 degrees to correct for the drift. After the update, Spirit re-acquired images from the same location to allow the science team to accurately target future observations. |
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#4
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![]() Senior Member ![]() ![]() ![]() ![]() Group: Members Posts: 4252 Joined: 17-January 05 Member No.: 152 ![]() |
From http://marsrovers.jpl.nasa.gov/mission/status.html: QUOTE SPIRIT UPDATE: Spirit Perfects Pointing Parameters, Collects Images Large and Small - sol 855-859, June 1, 2006: Since arriving at the rover's current location on the 807th sol, or Martian day, of exploration (April 10, 2006), Spirit's knowledge of its attitude relative to the sun has drifted. The rover uses an onboard computer to keep track of attitude changes, but error builds up in this measurement over time. Anyone understand what the nature of this drift is? I thought that normally this drift occured when the rover was driving, and hence accumulating errors while its orientation changes. In this case Spirit has been sitting still, and hasn't even settled according to the images. If it's orientation was known 50 sols ago it should be known as accurately tosol! |
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#5
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![]() Member ![]() ![]() ![]() Group: Members Posts: 408 Joined: 3-August 05 Member No.: 453 ![]() |
Anyone understand what the nature of this drift is? A small bias in the noise levels of the gyros that would add up to a measurable change over many days? But that would be true when driving too, so what is so special now? The rover can still update its orientation based on sun angles, which could (would?) reset the attitude vectors I would think. Hm, a puzzle indeed... Airbag |
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#6
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![]() Dublin Correspondent ![]() ![]() ![]() ![]() Group: Admin Posts: 1799 Joined: 28-March 05 From: Celbridge, Ireland Member No.: 220 ![]() |
The rover can still update its orientation based on sun angles, which could (would?) reset the attitude vectors I would think. The JPL update confirmed James' third alternative. The precision of the knowledge of the orientation of the rover was improved because they had many more sun pointing shots over time with which to refine the calculation. |
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#7
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![]() Member ![]() ![]() ![]() Group: Members Posts: 408 Joined: 3-August 05 Member No.: 453 ![]() |
The JPL update confirmed James' third alternative. The precision of the knowledge of the orientation of the rover was improved because they had many more sun pointing shots over time with which to refine the calculation. This issue is perhaps not as straighforward as it might seem - at least to me. Those Sun images are roughly 20 pixels across, and let's assume the centroid can be measured to within 1 pixel. Since the Sun's angular diameter as seen from Mars is about .35 degrees, the position of the Sun can in theory be measured to within say .015 degrees. This is of course assuming the rover's position is know (it is), and the rovers's clock and Pancam pointing accuracy are at least as good as the measurements require. Then, a series of measurement with the Sun near the zenith (to avoid refractive effects, which can't be that big a deal on Mars anyway) can be used to obtain the rover's pitch and roll, assuming a reasonable knowledge of its yaw. Yaw can not easily be measured this way - think of it this way, the Sun at zenith would look the same for all yaw values (assuming a level rover). Towards sunset a similar set of measurements can be used to refine yaw as even refractive effects would not affect the "sideways" position of the Sun is the sky. These new measurements would then be fed into the next cycle. Given the in theory very accurate measurements of the Sun's centroid, I presume then that it is a greater inaccuracy of the rover's clock and/or Pancam pointing accuracy that limits the rover's attitude accuracy and hence benefits from averaging over multiple solls? Well, a fascinating topic I think, and I'd be interested to learn more if anybody has any more information (as opposed to my speculation ![]() Airbag. |
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#8
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![]() Dublin Correspondent ![]() ![]() ![]() ![]() Group: Admin Posts: 1799 Joined: 28-March 05 From: Celbridge, Ireland Member No.: 220 ![]() |
Then, a series of measurement with the Sun near the zenith (to avoid refractive effects, which can't be that big a deal on Mars anyway) can be used to obtain the rover's pitch and roll, assuming a reasonable knowledge of its yaw. Yaw can not easily be measured this way - think of it this way, the Sun at zenith would look the same for all yaw values (assuming a level rover). Airbag. True but: A: The rover is not level. B: The sun shots are taken at a variety of times of day not just one. C: In this case we have sun shots taken over an extended period of time and the suns overall track has changed significantly (at least relative to the accuracy of the Pancam). Its a very interesting topic all the same. |
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#9
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![]() Member ![]() ![]() ![]() Group: Members Posts: 408 Joined: 3-August 05 Member No.: 453 ![]() |
True but: A: The rover is not level. B: The sun shots are taken at a variety of times of day not just one. C: In this case we have sun shots taken over an extended period of time and the suns overall track has changed significantly (at least relative to the accuracy of the Pancam). Its a very interesting topic all the same. Some thoughts on your comments: A: For the purposes of these hand waving arguments, I'd say 11 degrees is effectively level (as compared to the 90 degrees zenith angle). B: I suggested two sets of measurements should be sufficient. Looking at the positions of the Sun shots (using MMB's pano mode for sols 807-855), it appears the measurements fall into two clusters - one near the zenith, and the other about 20-30 degrees above the horizon, with some outliers in between. C: This I believe is at the heart of the issue, assuming the Pancam pointing knowledge is indeed less than the Sun's measured accuracy (in pixels). This link states the pointing knowledge is 0.1 degrees, which although about a magnitude larger than my centroid accuracy estimates above, is still much less than the almost 2 degrees attitude adjustment. So I'm still puzzled why the adjustment was so large. Airbag |
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