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Movie of OSIRIS-REx’s last rehearsal before sample grab

Closest point to Nighingale landing site during OSIRIS-REx's last rehearsal
Click image for full movie.

The OSIRIS-REx science team has released a movie made by the spacecraft’s navigation camera during its August 11th final rehearsal prior to the planned sample grab-and-go now set for October.

The image to the right is a capture of one image when the spacecraft was closest to the asteroid, about 131 feet above the surface. The target landing site, dubbed Nightingale, is the somewhat smooth area near the top half of the frame.

These images were captured over a three-hour period – the imaging sequence begins approximately one hour after the orbit departure maneuver and ends approximately two minutes after the back-away burn. In the middle of the sequence, the spacecraft slews, or rotates, so that NavCam 2 looks away from Bennu, toward space. Shortly after, it performs a final slew to point the camera (and the sampling arm) toward the surface again. Near the end of the sequence, site Nightingale comes into view at the top of the frame. The large, tall boulder situated on the crater’s rim (upper left) is 43 feet (13 meters) on its longest axis. The sequence was created using nearly 300 images taken by the spacecraft’s NavCam 2 camera.

Nightingale might be their best choice, but it remains about half the size they had originally wanted for their grab-and-go site, with far too many objects larger than planned. They designed the grab-and-go equipment to catch objects smaller than 0.8 inches. Little at this location, or on the entire surface of Bennu, is that small. The asteroid is truly a pile of gravel, with no dust.

Conscious Choice cover

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  • Chris

    So two items here:

    Why can’t the OSIRUS-REx simply maneuver slowly and gradually to the surface? Why does it need to be a bounce down grab and go?

    The desire here is to get essentially dust or small pebbles. I still maintain that if this thing is really just a pile of rubble loosly held together by its own gravity then all the dust and smaller items are probably in the center. This would be caused by any disturbance due to other bodies, moons, planets etc “shaking” the rubble. If you take a pile of rocks and pebbles and sand and vibrate it the smaller items fall through the larger items. Bennu’s gravity points to its center – that’s where I think the dust is.

  • Chris: Several points that might help answer your questions about their technique of sample grab.

    1. The spacecraft must work autonomously. They designed it with that limitation in mind.

    2. They had never seen a rubble pile asteroid when they designed the spacecraft, so they could only guess at what they’d find, based on what has been seen with every other asteroid so far visited. None however were anything like Bennu (or Ryugu for that matter).

    3. The rocks on Bennu are held in place by a very tiny gravity. Touch it, and they will be greatly disturbed, and fly everywhere. (Search BtB for “Ryugu” and “Hayabusa-2” and you will find the movie of that spacecraft’s sample grab. Watch how everything flies wildly when they touch the surface.

    Coming in slowly means the spacecraft is exposed to this flying debris longer. In this area they guessed right (without every seeing a rubble pile asteroid like this). You need to get in and out quick or else you risk getting hit badly by something.

    4. You are absolutely right about the dust. The scientists themselves believe it has settled inward.

  • Chris

    Hi Bob,

    I understand that the structure of Bennu is different than expected. (That it is different is probably a joy.) On moving in for a closer look the issue I see is that the time (sample time) between making a position correction and then seeing what the actual new position is long. (distance, speed of light, reaction time on thrusters…etc.) That means that moving close would need to be made in smaller and smaller steps; with less and less adjustment as you come in. But I would think the spacecraft could essentially track closer and closer to the asteroid. This way the bounce in, grab, and go has a much lower velocity… Or even a “landing” this way there is no large disturbance of the rubble pile. The key in my mind is to move very slowly. This will also cause much less disturbance of the surface.
    There may be some other dynamic at work here that I don’t know about such as a relative spin of the rubble pile that would make the maneuver I am proposing more difficult.

  • LocalFluff

    Remember NASA’s (well, White House really) crazy idea to send astronauts to an asteroid like this? An EVA astronaut digging into this stuff would’ve been surrounded by a cloud of rocks and dust. They wouldn’t even have done an EVA, but just look at it and then go back home again.

    Then the even crazier idea to instead use an uncrewed tug to tow one of these things to Lunar orbit (to do the astronaut EVA there instead, which they wouldn’t have). That would hardly have worked as the thing disintegrates when pushed.

    They then proposed to pick up a boulder from a NEA, that might’ve worked. That would only have been be a bigger sample collection mission.

    The range of different concepts for asteroid redirect proposals, for Earth’s defense against impacts, can be narrowed down a bit now. Impactors, physical pushing and heating an asteroid on one side to let out gassing drive it away, can probably be dismissed now that 2 out of 2 asteroid sample return missions have found rubble piles

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