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by rfdonnelly
1919 days ago
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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. |
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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...