What are these?

2 months ago by dingbizcuit to c/perseverancerover

I see these images almost every day. What are they? Is that the sun and are they recording or sampling atmospheric conditions? In the past they were preceded by four images of star fields (if you download and zoom in.) What are those? (Image in comments). Are they related? Credit: NASA/JPL

Promethiel 10 points 2 months ago

It is the sun, yeah. They use the Perseverance cams to monitor solar activity.

https://www.jpl.nasa.gov/...

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paulhammond5155 9 points 2 months ago

The images you highlighted in your post are MastCam-Z images of the sun taken through neutral density (ND) filters that are used for solar imaging. Each of the MastCam-Z cameras has a pair of ND filters (590 ± 88 nm (ND6) and 880 ± 10 nm (ND5))

They image the sun on a regular basis, primarily to check the rover's internal navigation system, but they also use the cameras with those filters to measure sunspot activity, especially when Mars is on the far side of the sun, they have also measured the Martian moons transiting the sun, this can more accurately measure the rotation speeds and orbits of the moons compared with Earth based telescopes.

I'm assuming this set of images were acquired on sol 1944 for navigation checks. Basically the rover have a set of internal motion detectors, they are used during driving and at the end of each drive to record the position of the rover. That x, y & z data is returned to JPL shortly after each drive. That data permits the update of the rover traverse and location maps. However there can be minor inaccuracies (e.g caused by wheel slip on slopes or soft sand), but those small errors can accumulate over several drives where the rover's computer thinks it is in a certain location, but it's slightly off. So they use the sun to accurately check the actual position. The way I understand it (from MSL days) is that the rover points the camera at where it calculates the sun should be at a specific time of the day (if its navigation is accurate) and snaps a photo. If it is accurate the sun will appear in the center of the images, if the navigation is off (even by a little) the sun will be 'off-center' in the image and ground engineering team members can reset the x, y & z accordingly. The amount it is off-center can be used to accurately calibrate / correct its location. These sun checks are similar to how navigators sailed the seven seas back in the day with a sextant. The sun images are used in conjunction with end-of-drive images to determine accurate location :)

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dingbizcuit 2 points 2 months ago

Hey Paul, I really appreciate your detailed responses. Now when I sort threw the raw images I know what they are for!!!! This makes it fun as I can now stop and try to determine how far off the rover is. Looks like it was fairly close on 1942 and 1944 if I'm reading them right, a little high?

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paulhammond5155 1 point 2 months ago

Hey Paul, I really appreciate your detailed responses. Now when I sort threw the raw images I know what they are for!!! This makes it fun as I can now stop and try to determine how far off the rover is. Looks like it was fairly close on 1942 and 1944 if I’m reading them right, a little high?

Just a little off, not bad when you consider that as well as understanding the estimated location, they have to take into consideration, the yaw of the rover, as well as the roll and the pitch. When they have drifted by whatever limits they set themselves, they reset the rover's 'frame' these are known as sites (you can see them on the drive reports that are shared here.

Depending on the terrain, they reset the site number when required, this happens on average about every 13 to 15 drives, but in challenging terrain it can happen more frequently. They just reset the site number to 91 at the end of the last drive (sol 1947). Which is not bad considering that they have only driven 546 times since landing, so their internal navigation, which is based on the motion sensors are pretty accurate.

At the end of the last drive (Sol 1947) they adjusted the drive distance by just 16cm having driven 1212 meters since the last reset, so I think that shows that the motion sensors are very accurate :)

I'd post more drive images, but Lemmy times out when I am trying to upload. I'll try again later.

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paulhammond5155 1 point 2 months ago

Hey Paul

Check this out from some recent images

NASA’s Perseverance rover watches Earth vanish from the surface of Mars

https://www.sciencedaily.com/...

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dingbizcuit 8 points 2 months ago

Credit: NASA/JPL

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paulhammond5155 4 points 2 months ago

Which sols are the images you highlighted in the image in your comment?

It is possible that the rover returned metadata to show the pointing and the precise UTC timing of the capture by the camera when those 4 images were acquired. Such data can be used by experts to understand what star field camera was looking at, but that's a skill I have not acquired. The actual reason for the images will likely be detailed in the mission managers report for that sol, but if they are recent images, then you'll have to wait several months before that information hits the PDS / Analysts Notebook

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