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Reprojecting the Perseverance landing footage onto satellite imagery

matthewearl.github.io

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Re: Reprojecting the Perseverance landing footage onto satellite imagery

#12

Post by pkaye »

milofeynman wrote: post #7

I've been having trouble finding the answer to this. How close to it's intended target did it land? Thanks

I was designed to have an error under 40m. I don't what it accomplished.

https://arstechnica.com/science/2019/10/heres-an-example-of-...

Re: Reprojecting the Perseverance landing footage onto satellite imagery

#13

Post by rfdonnelly »

milofeynman wrote: post #7

I've been having trouble finding the answer to this. How close to it's intended target did it land? Thanks

5 meters. However, the "intended target" is not simply defined.

The landing ellipse for Perseverance was 7.7km by 6.6km. The goal is to land at a safe spot within the ellipse rather than land at a specific location.

The new Terrain Relative Navigation capability determines the rovers position relative to the surface during descent by comparing camera images to onboard satellite imagery. On Earth you'd use GPS. No GPS on Mars.

Once the rover knows it's position, it can now determine the safest spot to land using an onboard hazard map. The spot it chose to land at vs the spot it actually landed at was 5 meters apart.

Re: Reprojecting the Perseverance landing footage onto satellite imagery

#14

Post by bertylicious »

twright wrote: post #6

Excellent post! I wonder why SIFT didn't find sufficient keypoints early on, it's typically a beast of a method for such a task. It looks like there's some intensity variation, the satellite image is darker, but I'm not sure that would explain it all.

The SIFT algorithm discards low contrast keypoints. In the beginning the surface looks quite blurry (it seems the camera is auto-focusing the heat shield) which probably causes only low quality keypoints to be found on the surface. Additionally, if the algorithm also capped the maximum number of keypoints per image, the situation gets even worse, because strong keypoints on the heat shield (which had to be discarded "manually" later) compete against weak keypoints on the surface.

Re: Reprojecting the Perseverance landing footage onto satellite imagery

#15

Post by Laremere »

milofeynman wrote: post #7

I've been having trouble finding the answer to this. How close to it's intended target did it land? Thanks

You can see the map of where it landed and it's path moving here: https://mars.nasa.gov/mars2020/mission/where-is-the-rover/

The yellow oval is the target landing zone, though it looks like it's a bit too tall on this map compared to other sources.

You can see it's landing targets within the oval here: https://www.jpl.nasa.gov/images/jezeros-hazard-map

So it looks like it landed a little over 1km from the center of the oval, if that's your question.

When precisely talking about space travel, things tend to be discussed as "nominal" instead of being on target or correct. This is because some variance is expected, and systems are designed to work successfully within that variance. In that sense, Perseverance landed within the landing oval and on a safe landing spot, so it was 0 meters away from target.

An analogy would be it hit the bullseye and got the points, even it if it wasn't exactly in the middle of the dart board.

Re: Reprojecting the Perseverance landing footage onto satellite imagery

#17

Post by saulrh »

It'd be pretty neat to lift this up into 3d - you could probably reverse the transforms to find the camera pose for each frame, then drop it into a scene alongside the camera frustum and the topography so we can see exactly how much steering the descent stage did to hit its target and how fast it was descending at every stage.

Re: Reprojecting the Perseverance landing footage onto satellite imagery

#20

Post by Cogito »

rfdonnelly wrote: post #13
milofeynman wrote: post #7

I've been having trouble finding the answer to this. How close to it's intended target did it land? Thanks

5 meters. However, the "intended target" is not simply defined. The landing ellipse for Perseverance was 7.7km by 6.6km. The goal is to land at a safe spot within the ellipse rather than land at a specific location. The new Terrain Relative Navigation capability determines the rovers position relative to the surface during descent by comparing camera images to onboard satellite imagery. On Earth you'd use GPS. No GPS…

> Once the rover knows it's position, it can now determine the safest spot to land using an onboard hazard map. The spot it chose to land at vs the spot it actually landed at was 5 meters apart.

To add a bit more info, poorly remembered from this excellent We Martians episode[0] interviewing Swati Mohan, who is the Mars 2020 Guidance, Navigation and Controls Operations Lead and was the voice of the landing. Go listen to it!

On the way down an image is taken. Using data about how the atmospheric entry is going, and with a lot of constraints that include the hazard map and what kinds of manoeuvres are possible with the descent system (in particular it does a divert and there are minimum and maximum distances the divert must lie between), a single pixel is chosen from that image to aim for. That pixel represents a 10m x 10m square, and the rover landed with 5m of that square.

The hazard map is created from images with a 1m x 1m resolution, from one of the orbiters (Mars Reconnaissance Orbiter I think). Those images are scaled down for the hazard map, as the on-board image processing had very tight bounds on how long it could search for a valid landing site. The podcast goes into some cool detail about that whole system and its technical design.

0: https://wemartians.com/podcasts/94-guiding-perseverance-to-t...

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