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

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.

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.

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.