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Post-Sampling & Earth Return
nprev
post Oct 24 2020, 07:02 AM
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Now that the 'boop' has been completed (with spectacular success!), we'll move the discussion to here for subsequent mission events. smile.gif


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walfy
post Oct 24 2020, 08:37 AM
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Boosted the shadows to reveal what I assume are the rocks wedged in the mylar flap. Looks like our little robot gorged like a T-REx!
Attached Image


The third image in the sequence was the most over exposed, so the rocks hiding in the shadows are the least grainy when revealed:
Attached Image

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dsmillman
post Oct 24 2020, 01:30 PM
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The audio of the 10/23/2020 teleconference can be accessed for 30 days at:

1-866-373-4996
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Tom Tamlyn
post Oct 24 2020, 06:55 PM
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Thanks to for that link.

It was a great press conference. Even though Brian's helpful summary covered most of the the major points, it made fascinating listening, with detailed, clear, and fluent presentations and answers from Dante Lauretta and Thomas Zurbuchen, and sharp, business-like questions from well-informed reporters.

The stow operation is currently expected to begin on Tuesday. As Brian mentioned, the mission is seeking substantial extra DSN coverage in order to do something unusual for robotic spacecraft: conduct an operation interactively with "the ground in the loop." The revised stow plan will have a number of check points, at which the operation will pause while images are downloaded and analyzed to determine whether to proceed with the plan or try something different. As a result the stow operation is expected to last three days, instead of several hours as originally planned.

The previously scheduled activity of spinning the spacecraft with the arm extended to obtain a moment of inertia measurement has been cancelled, and Lauretta pretty much ruled out any other possibility for measuring the sample mass (as opposed to estimating the mass from images) prior to landing. However, he did seem to acknowledge that there had not been any occasion to think about a different way such a measurement could be taken during the return trip. I suppose it's possible they might come up with a way to tease some sample mass information out of trajectory telemetry during the return voyage.
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JRehling
post Oct 24 2020, 07:24 PM
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Looking at the apparent fragility of those "rocks" I wonder what is going to happen during the high g forces during entry. None of it will vanish, but it might lose some of the original structure.
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marsbug
post Oct 24 2020, 09:18 PM
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It's a nice problem to have in a way... but it's still a problem . Still it sounds like the team have it in hand.


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Explorer1
post Oct 24 2020, 09:56 PM
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QUOTE (Tom Tamlyn @ Oct 24 2020, 01:55 PM) *
However, he did seem to acknowledge that there had not been any occasion to think about a different way such a measurement could be taken during the return trip. I suppose it's possible they might come up with a way to tease some sample mass information out of trajectory telemetry during the return voyage.

Assuming the mass without the sample (including fuel and subtracting the nitrogen gas used) is known precisely enough, there should be a slight difference in how it 'handles' during maneuvers like the Earth return burn and any TCMs.
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dtolman
post Oct 24 2020, 10:42 PM
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So they cancelled the spin because visual inspection confirmed an abundance of material?
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Marcin600
post Oct 25 2020, 12:33 AM
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QUOTE (dtolman @ Oct 25 2020, 12:42 AM) *
So they cancelled the spin because visual inspection confirmed an abundance of material?


"...To preserve the remaining material..."
"...Any movement to the spacecraft and the TAGSAM instrument may lead to further sample loss..."
"...The loss of mass is of concern to me, so I’m strongly encouraging the team to stow this precious sample as quickly as possible - said Dante Lauretta..."
["some of sample particles appeared to be escaping slowly from the TAGSAM head - passing through small gaps where a mylar flap is slightly wedged open by larger rocks"]
(here)

I think that with very gentle and careful moving the TAGSAM head while enclosing it in the return capsule, and doing it without undue delay, the final loss of the collected mass (they collected about 400 g - much more than planned 60 g) will be insignificant. We have to keep our fingers crossed for this
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Reed
post Oct 25 2020, 06:32 AM
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QUOTE (dsmillman @ Oct 24 2020, 06:30 AM) *
The audio of the 10/23/2020 teleconference can be accessed for 30 days at:

FWIW, also on youtube (starts at ~13 minutes) https://www.youtube.com/watch?v=n274YX4xk_0 - just audio except for showing the gif from the press release for a while
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rlorenz
post Oct 25 2020, 10:16 PM
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QUOTE (Explorer1 @ Oct 24 2020, 05:56 PM) *
Assuming the mass without the sample (including fuel and subtracting the nitrogen gas used) is known precisely enough, there should be a slight difference in how it 'handles' during maneuvers like the Earth return burn and any TCMs.


In theory, yes (I think I remember reading a scifi story where a stowaway on a spacecraft is discovered this way). But in practice, this is a very small signal to look for (if you want to measure a 400g sample to 10%, as part of a 400kg spacecraft, that's a 0.01% precision)

I think thruster performance is probably not more consistent than 1%, maybe worse.

Measuring spin rates, and changes therein is something that can be done with exquisite precision, but more particularly putting the sample mass out on the TAGSAM arm gives a large moment arm, so the sample mass 'signal' component of the vehicle's moment of inertia. So having a viable retrieval of sample mass from this spin exercise does not mean you can do it with useful precision in a translation manoeuvre....
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mcaplinger
post Oct 25 2020, 11:21 PM
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QUOTE (rlorenz @ Oct 25 2020, 02:16 PM) *
In theory, yes (I think I remember reading a scifi story where a stowaway on a spacecraft is discovered this way). But in practice, this is a very small signal to look for (if you want to measure a 400g sample to 10%, as part of a 400kg spacecraft, that's a 0.01% precision)... I think thruster performance is probably not more consistent than 1%, maybe worse.

Agreed, I don't think thruster firing is going to tell you anything.

But the other small forces on the spacecraft (e.g., radiation pressure) might be well enough characterized. Time will tell.

The story is of course https://en.wikipedia.org/wiki/The_Cold_Equations


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JRehling
post Oct 26 2020, 03:58 AM
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Apollo 13 had a bit of a concern regarding sample mass, but it was an issue of many kg, not g:

http://www.collectspace.com/news/news-0416..._souvenirs.html
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stevesliva
post Oct 26 2020, 01:50 PM
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QUOTE (mcaplinger post Oct 23 2020 @ 06:56 PM Post #210)
One thing that surprised me was Dante talking about "dust loading" (I think he said) on Navcam and SamCam. I wonder how dirty the nadir panel of the spacecraft is now?


Any word on this? I wonder in the context of an extended mission (proposal? idea?).
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jccwrt
post Oct 26 2020, 05:39 PM
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If Bennu regolith is anywhere near as sticky as lunar regolith, that whole part of the spacecraft is probably filthy from the compressed nitrogen burst.
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