Hayabusa2 descends from Home Position to take its first close look at Ryugu
JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST.
Ryugu from Hayabusa2, 20 July 2018
Hayabusa2 obtained this image from a position less than 6 kilometers away from Ryugu's surface on 20 July 2018 at around 07:00 UTC. Near the center is a bowl-shaped crater, the largest on the asteroid.
With home base -- also known as the "Box A" position -- established, the spacecraft can now take two kinds of excursions. Taking the asteroid as being "down" from Hayabusa2 (that is, in the -Z direction)*, the spacecraft can now venture to all sides of Home position, 10 kilometers in the X or Y directions. Hayabusa2 will be able to view the asteroid from different angles and under different lighting conditions. Hayabusa2 navigators refer to this region, 10 kilometers in X and Y directions, as "Box B."
Another maneuvering zone contains Box A and allows Hayabusa2 to descend to within 5 kilometers of the asteroid's surface. This is called "Box C." Hayabusa2 left Box A for the first time on July 17, arrived at the bottom of Box C on July 20, spent a day there, and returned to Home position in Box A on July 25. The images that Hayabusa2 took from the bottom of Box C reveal meter-sized boulders and will help the team begin to select potential landing sites.
* What defines the precise "down" direction for Hayabusa2, though? I had initially assumed that "down" was "away from the Sun," but this is NOT true. The Hayabusa2 team actually defines "down" as "away from Earth," which makes sense as a coordinate system when your mission's biggest challenge is navigating precisely around a low-gravity object. From two-way light-time measurements, the navigators can very precisely track Hayabusa2's change in distance with respect to the asteroid.