Dawn Drops To 1470km Orbit, Snaps Sharper Pictures of Ceres

An anonymous reader writes: NASA's Dawn spacecraft, after an extensive series of high orbits around Ceres, has now dropped to just 1,470 kilometers over the dwarf planet's surface. It has begun an 11-day process to map the entirety of Ceres, which it will repeat several times over the next couple months. Its lower orbit now allows photo resolution of ~140 meters per pixel, and it has sent back some great images. "Engineers and scientists will also refine their measurements of Ceres' gravity field, which will help mission planners in designing Dawn's next orbit — its lowest — as well as the journey to get there. In late October, Dawn will begin spiraling toward this final orbit, which will be at an altitude of 230 miles (375 kilometers)."

Comments

Re:how low can it go?

[stevelinton]

as there is no atmosphere could it get down to a mountain scraping orbit? Just high enough to get round the lumps and bumps and variability in the roundness of the object? Would that enable it to image things at a really small pixel size?

Apart from the question of what range the instruments were designed tooperaqte best at, the other problem is the unevenness of Ceres gravity. They are mapping that now, but it's unlikely the mass of Ceres is perfectly symmetrically arranged, so the gravity will be uneven. Those unevennesses distort the orbit and cause it to change over time. If you're 300 km away that's not a big problem, except that you occasionally have to use up some reaction mass to get back where you want to be. At 10km it would probabl;y be disasterous.

For the same reason it's very hard to keep a probe in a stable orbit less than 100km or so above Earth's moon.