TEGA (Thermal Evolved Gas Analyzer), an apparent problem Options

[Skyrunner]

Or as my old AP Physics teacher from high school would say, "If at first you don't succeed, use a hammer."

Or as the first tenet in mechanical engineering goes:
"If the brute force fails to work,
try using more of it"

[djellison]

Mythbusters
"With enough lubrication, we can do anything"



Doug

[Littlebit]

I was wondering the accuracy of the samples (on both TEGA and MECA). Obviously the payload engineers went through great lengths to make the instruments as accurate as possible. But what makes me wonder is the temperature gradient. The soil is much colder than the lander deck (and instruments). We now this from METs temperature sensors as well as engineering calculations. Small differences in temperature could (at least in theory) lead to out gassing in the sample so that immediately after the sample is scooped up it could start out gassing. After the sample is dumped in the instrument of choice (before closing its lid) or when the arm is above deck, it heats up even more, encouraging more out gassing. Yes, the out gassing shouldn't be that much but still....it make me wonder about the accuracy and the precautions taken.

Soil sampling is rarely entirely representive. In the Martian polar climes, where there are radical swings in temperature and soil shifting due to growth and shrinkage of the polar cap, you would expect a dynamic stability - ultra light molecules are gone, water ammonia and such just below the surface will sublime, but not terribly quickly at these temperatures and pressures. The samples should be highly representative, maybe off a few percent in the most volatile chemicals found.

[ilbasso]

Mythbusters
"With enough lubrication, we can do anything"



Doug

Anybody remember the Firesign Theatre and Fudd's First Law of Opposition? "If you push something hard enough, it will fall over."

[mike]

What about a flat plate resting long axes parallel to the eternally flat ground.. on the planet Flatia.. I suppose you could push it so hard it moves into space, at which point it will eventually fall onto something.. but it might fall onto an evil entity of some kind, like say an anti-happiness consortium

[Guest_Zvezdichko_*]

http://phoenix.lpl.arizona.edu/06_07_pr.php - sample released, "but the instrument did not confirm that any of the sample passed through the screen."

[Harder]

This first sample is "topsoil" where the 1 mm mesh screen can be expected to pass thru the finer material - or perhaps not, as we now seem to find out.

But to expect that ice-type matl scraped from deeper trenches will pass thru such a fine mesh screen seems completely impossible. I´m really flabbergasted to learn about the existence of this fine mesh screen today. Surely the design team has thought through the scenario of delivering ice and created a couple of bins without a screen? Take the test by getting a scoop of sorbet ice from your deepfreezer - the only way to get scraps of sorbet ice through any screen, no matter the mesh size, is by melting! But on Mars the sublimation will happen first.

Too pessimistric a view? I really, sincerely hope I overlook something here!

[ugordan]

Too pessimistric a view? I really, sincerely hope I overlook something here!

I was under the impression they're primarily interested in stuff potentially mixed in (dissolved?) in the ice, not ice per se. Even if ice sublimates away (and it only sublimates really fast when you have isolated small particles of ice, not loads of them), the other stuff will be left behind.

[Guest_Sunspot_*]

Oh Dear, things don't seem to be going too well.

[01101001]

But to expect that ice-type matl scraped from deeper trenches will pass thru such a fine mesh screen seems completely impossible.

How large to you expect the rasped ice particles to be?

RASP SAMPLE ACQUISITION ON THE PHOENIX MARS SCOUT MISSION (PDF)

The rasping operation powderizes materials while
it is cutting them free. In a few seconds and in a single
operation, rasp systems cut away strong materials,
process them to sizes that are instrument-ingestible,
and capture them in a catch container.
[...]
Conclusions: Rasping with the current ISAD RASP
bit design can remove a significant fraction of H2O in
permafrost samples. This is on top of passive sublimation
that takes place as the sample is transferred to the
instruments to be analyzed.

But the fraction looked to be 10 to 30 percent depending on weather.

[Harder]

Thanks for this info. It states that the rasp produces cuttings that are instrument-digestible. I can imagine that ice/permafrost as hard as stone will indeed be rasped into finer pieces which are immediately suitable to pass through the funnel of the TEGA. So why install a fine mesh screen in the first place, especialy since icy particles have some tendency to bind together and won´t pass at all thru a strainer just by the force of gravity?

Perhaps my misunderstanding is because icy particles/crystals on earth have some liquid water which creates these coagulation effects (like snow flakes) whereas on Mars liquid water is not forming at all. Even here there is a shadow of a doubt, due to the heat imparted by the rasp which might create temporary softening/melting of ice in rasp cuttings.

[bgarlick]

The screen behind the TEGA doors looks very fine meshed and the soil looks very clumpy. I would not be surprised if they have a real hard
time getting any material through that screen. Is there a way for them to tell how much material is in the oven before closing the oven and starting the baking?

Darn! It looks like my concern back on the 4th was not completely unfounded...
I wonder if they have the dexterity to use the RA scoop to manually 'smoosh' some of the soil through the TEGA screen, or at least press down on the soil on the screen with the scoop while the shakers are activated.

[brianc]

Darn! It looks like my concern back on the 4th was not completely unfounded...
I wonder if they have the dexterity to use the RA scoop to manually 'smoosh' some of the soil through the TEGA screen, or at least press down on the soil on the screen with the scoop while the shakers are activated.

A wee tap with the scoop on the end of the arm should do the trick. My wealth of DIY projects leaves with me with the conclusion that there are few jobs that can't be completed with the aid of a hammer and screwdriver and the scoop looks like the sort of thing I would use as a hammer, actually my dad (god rest his soul) may well have used the scoop edge as a screwdriver substitute, I seem to recall him using mother's cutlery as proxy-screwdrivers !

[MahFL]

Oh oh, lots of head scratching at UA.

[Stu]

Well, head-scratching is good, you know? Doesn't do to take success for granted, and Mars takes a perverse delight in making us work for the knowledge we gather there. This is just one more thing to work out, isn't it? This spacecraft has been tested to within an inch of its life, but they couldn't predict every possible problem. I'm sure they'll figure something out.

If all else fails, Phoenix's passenger can pat the dirt with a paw, after his heroic efforts removing the bio-barrier earlier in the mission...

(No, seriously... packing a cat into a Faberge egg and ejecting it from Phoenix??... who thought that up? And where can I buy some of whatever they were on when they did? )