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Asteroid approach, Science operations begin!
Holder of the Tw...
post Nov 30 2018, 05:17 PM
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I guess the best word I can think of here is "ironic".

Hayabusa 2 was planned with three sample acquisitions in mind, with the idea of getting diverse samples. But Ryugu turned out to appear fairly homogeneous so now they are only planning one sample (what about the sub surface sampling though? But I digress... ).

Then you have OSIRIS-REx only planning one single sample grab from Bennu.

I know they haven't reported anything yet about any of Bennu's compositional differences but, well... just look at it.

Technically, they could make three tries at sampling, provided the canister didn't fill up on the first try, so I wonder if they might rethink things.

Also, I'm a little worried at this point. OSIRIS-REx seems to be counting on there being dust and small pebbles for its sampling. It is still too far from Bennu to tell, but if the surface turns out to be like Ryugu with nothing but larger pebbles and rocks available, I wonder how they will deal with that.
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tanjent
post Nov 30 2018, 07:08 PM
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That's a nice side-by side comparison of the three bodies, and it is consistent with the unexpectedly rocky surface of Ryuku and likely Bennu too.

Isn't that how panning for gold works? If you put heterogeneous gravel in a pan and agitate it, the smaller particles will settle to the bottom and the larger chunks will "float" to the top, even if they are intrinsically denser, because their irregular shapes prevent them from packing together as tightly. So in a rubble pile asteroid, the finer material will tend to migrate to the center. Itokawa probably had a bit more structural rigidity than the other two, at least enough to prevent this sorting process from proceeding quite so far.

The similar slightly oblate shapes of Ryugu and Bennu seem to reflect a balance between centrifugal force and their minimal gravity which may prove to be the norm for very loosely accreted piles of variously-sized junk.
If so, it may well complicate the sample collection process as Holder suggests.
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Adam Hurcewicz
post Dec 2 2018, 01:05 PM
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OSIRIS-REx Arrival to Bennu (3-18 Dec 2018)


https://www.youtube.com/watch?v=Yrc4jR3Gy5M


I use SPICE (bsp,bc,tsc,tpc,tf) files from NAIF/NASA
Model of OREX is from NASA 3D models converted to cmod.

Soft is Celestia 1.7 64bit

More info apout arrival :
https://www.asteroidmission.org/asteroid-operations/


Attached Image


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Daniele_bianchin...
post Dec 3 2018, 11:30 AM
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I allowed myself to revisit Emily's comparison (Itokawa + Ryugu) and add asteroid Bennu:

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PhilipTerryGraha...
post Dec 3 2018, 05:55 PM
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This is what I'm assuming to be new, higher-resolution MapCam imagery. This GIF is featured on the mission's front page and the "spacecraft imagery" page, but clicking on the link (https://www.asteroidmission.org/?attachment_id=12095#main) leads to a 404... Anyways, many congratulations to the OSIRIS-REx team for completing the long journey to Bennu! I wish nothing but the very best for the mission ahead!


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Holder of the Tw...
post Dec 3 2018, 07:08 PM
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At the OSIRIS-REx website, the caption for the above image sequence reads as follows:

QUOTE
This series of images taken by the OSIRIS-REx spacecraft shows Bennu in one full rotation from a distance of around 50 miles (80 km). The spacecraft’s PolyCam camera obtained the thirty-six 2.2-millisecond frames over a period of four hours and 18 minutes.

Date Taken: Nov. 25, 2018

Instrument Used: OCAMS (PolyCam)

Credits: NASA's Goddard Space Flight Center/University of Arizona


Congratulations to the spacecraft team for a successful arrival today!
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vjkane
post Dec 3 2018, 08:31 PM
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I suspect it may take a lot of careful planning to find a safe touchdown surface on that asteroid.


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ElkGroveDan
post Dec 3 2018, 08:54 PM
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The first thing that stands out is how unusually sharp and angular the surface debris appears.


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Y Bar Ranch
post Dec 4 2018, 02:33 AM
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The animation makes it look like boulders should be flying off of it left and right. wink.gif

It'd be interesting to run a "Project Crowbar" to lever off one of the bigger boulders and drag/toss it into orbit for a full grapple and analysis.
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elakdawalla
post Dec 4 2018, 06:17 AM
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I pride myself on being able to discern solar system worlds, but if it were not for Ryugu's special polar boulder and Bennu's "pimple" boulder I would not be able to tell the two apart without consulting reference images.


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Hungry4info
post Dec 5 2018, 12:33 AM
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One thing that will help will be that the camera views aren't going to be constantly at full phase.

Here's Bennu at half phase from MapCam.
https://www.asteroidmission.org/20181203_mapcam/


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nprev
post Dec 5 2018, 03:13 AM
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Sure is a jagged little beast. Makes me wonder if the regolith is relatively fresh with less thermal & micrometeoritic weathering than we've seen on other comparable bodies.


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HSchirmer
post Dec 5 2018, 04:03 AM
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QUOTE (tanjent @ Nov 30 2018, 07:08 PM) *
...
Isn't that how panning for gold works? If you put heterogeneous gravel in a pan and agitate it, the smaller particles will settle to the bottom and the larger chunks will "float" to the top, even if they are intrinsically denser, because their irregular shapes prevent them from packing together as tightly.


Actually, what you're describing is "the Brasil Nut Effect" and there's even a paper on this
"The spherical Brazil Nut Effect and its significance to asteroids" https://academic.oup.com/mnras/article-pdf/...556/stu1388.pdf

Panning for gold is kinda the opposite, based on bulk density rather than grain size. Since gold is denser than stone, it is retained in the pan, or settles out into the grooves of a sluice, or if you're really old-school, settles out in the wool of a sheepskin...
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Holder of the Tw...
post Dec 5 2018, 05:47 PM
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High Phase Angle Picture taken seven hours before arrival by MapCam (click on link).

There will be a press conference December 10th to discuss the initial scientific results from approach, along with presentations at the AGU (American Geophysical Union) meeting on the 11th and 12th.

Press Conference Page

QUOTE
Get ready for some asteroid science. Now that OSIRIS-REx has arrived at Bennu, the mission team will be presenting the initial results of their scientific studies of the asteroid during the spacecraft’s Approach Phase. The highlights will be discussed at a press conference on Dec. 10 at the American Geophysical Union’s fall meeting in Washington, DC. For conference attendees, three special scientific sessions in collaboration with JAXA’s Hayabusa2 mission will explore the early results from both missions in more detail on Dec. 11 and 12
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Steve5304
post Dec 7 2018, 01:05 PM
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QUOTE (Holder of the Two Leashes @ Dec 5 2018, 05:47 PM) *
High Phase Angle Picture taken seven hours before arrival by MapCam (click on link).



The thing on the bottom left looks like a flat curled up sheet blink.gif

Its probably an optical illusion but man this thing has definitely collected a lot of rocky stuff over the years. Much different than Ryugu


Full Rotation

https://www.asteroidmission.org/?attachment_id=12182#main
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