Click for a higher resolution version.
On May 26 the OSIRIS-REx science team completed their first rehearsal and close approach to their back-up sample-grab-and-go site on Bennu, dubbed Osprey, getting as close as 820 feet. The image to the right, cropped and reduced to post here, shows that sample site within the white box. According to the image caption, the “long, light-colored boulder to the left of the dark patch, named Strix Saxum, is 17 ft (5.2 m) in length.” Note also that they have rotated the image so that east is at the top in order to make it more easily viewed.
This particular spot in this crater is actually a revision from their first choice from early in 2019, which originally was to the right and below the dark patch in the center of the crater. After six months of study, they decided instead on the present target area above the dark patch, because it seemed safer with the most sampleable material.
So how safe is this new location? Let’s take a closer look.
Click for full resolution.
The photo to the right is taken from the full resolution mosaic of today’s image [a very large file], and focuses specifically on the region in that white box. Even so, the image resolution is reduced. To see just this section at full resolution you need to click on the picture.
This is a very gravelly surface, with no dust, and many many pebbles larger than an inch across. Since OSIRIS-REx’s grab-and-go equipment is designed to collect objects smaller than 0.8 inches, there is a lot of stuff here that it can’t grab, but if disturbed could very well damage the spacecraft. And since Bennu’s gravity field is so weak, any contact with it will certainly disturb it, causing many of these pebbles to fly all over the place, as we saw when Japan’s Hayabusa-2 spacecraft did two touch-and-go sample grabs on the similar asteroid Ryugu. (Images from the first can be seen here, and a movie of the second here.)
In other words, the sample grab at Osprey would be a risky proposition.
If you are now saying thank goodness this is the back-up site, don’t. The primary site Nightingale is really not much better, and is probably as risky. The actual sample-grab-and-go at that primary site is presently scheduled for October 20, with a final rehearsal getting to about 131 feet set for August 11.
Keep your fingers crossed that all goes well. It will likely take a bit of praying to help the engineering.
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