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Unmanned Spaceflight.com > Mars & Missions > Past and Future > Phoenix
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helvick
QUOTE (ngunn @ Jun 7 2008, 11:03 PM) *
Is there such a thing as a H2O:CO2:chloride brine?

Seltzer..
elakdawalla
QUOTE (Harder @ Jun 7 2008, 10:16 AM) *
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?

There's a very good reason: the business end of TEGA, the oven itself, is a tiny quartz vial only a millimeter in diameter. If they let anything bigger into the doors, it would block the opening of the oven, and you'd get no sample.

--Emily
deglr6328
Mightn't we expect the MARDI microphone to be used sooner than expected now for trobleshooting, ie. to listen for TEGA mesh vibration?
Reed
Is there a diagram or detailed description of the layout of TEGA anywhere ? A quick google didn't turn up much beyond this page http://planetary.chem.tufts.edu/Phoenix/th...as_analyzer.htm
Aussie
QUOTE (Stu @ Jun 7 2008, 08:36 PM) *
but they couldn't predict every possible problem. I'm sure they'll figure something out.


I'm sure they will Stu. The MER team proved their innovation time and again. But Phoenix planners must have known that martian soil has clumping tendancies since Spirit took the close up on 18 January 2004. So they had a heads up and plenty of time to consider the implications of putting a fine mesh over the oven (although obviously that filter is required). With respect to rasped ice I would anticipate that they would have tested the theory in a Martian temperature/pressure simulated environment to make sure that the rasped ice didn't bond back together. They would have..wouldn't they? unsure.gif
SickNick
QUOTE (volcanopele @ Jun 6 2008, 06:30 PM) *
Or as my old AP Physics teacher from high school would say, "If at first you don't succeed, use a hammer."


Don't FORCE it, just use a bigger hammer...
SickNick
QUOTE (ngunn @ Jun 8 2008, 07:11 AM) *
Mars people please - I need some help with dismissing what is probably a daft idea. In the presence of salts it is possible for a wet soil to refuse to dry out completely; it just stays sticky. Is it possible for carbon dioxide ice to be saline, in the way that water ice can? Could that make it resist sublimation? For water, salt widens the gap between freezing and boiling, favouring the liquid state. Is it possible to imagine 'saline carbon dioxide' having a liquid phase on Mars, even transiently, that might make the soil sticky? I know. It's horrible. Shoot it down quickly please.


The behaviour of CO2-H2O mixtures is well understood over a wide range of temperatures and pressures. At Earth-normal conditions, CO2 dissolves slightly in water to form carbonated beverages and acid volcanic/mineral water. Solubility is better at higher pressure and lower temperature. At low temperature, a joint ice (Clathrate) is formed. This can form at up to 10C (above the melting point of pure water). Again, pressure favours clathrate formation.

it is not clear wheter CO2 clathrates are stable at mars near-surface conditions, but there is almost certainly SOME clathrates in the pole caps (On earth, the polar ice contains small amounts of Nitrogen, oxygen, and CO2 clathrates because trapped gas in snow is not entirely expelled from recrystallised ice. On Earth it's a curiosity. On Mars, it *might* be important, or it might not. (If the poles had a substantial CO2 clathrate component, they could be trapping a significant fraction of a whole atmosphere's woth of CO2, for example.

Excess CO2 *can* exist as a liquid at depth, above 5.2 bars and below 30C. This is unproven, but fun to speculate on...
dvandorn
QUOTE (SickNick @ Jun 7 2008, 09:43 PM) *
Don't FORCE it, just use a bigger hammer...

But just remember -- when the only tool you have is a hammer, most everything begins looking like a nail...

smile.gif

-the other Doug
deglr6328
QUOTE (SickNick @ Jun 8 2008, 02:51 AM) *
The behaviour of CO2-H2O mixtures is well understood over a wide range of temperatures and pressures. ..........

Excess CO2 *can* exist as a liquid at depth, above 5.2 bars and below 30C. This is unproven, but fun to speculate on...
=====================================
Nick Hoffman Mars Specialist
White Mars Research Unit



My heavens! It never ceases to amaze me the actual scientists and engineers who pop up on this site, it's fantastic. Though, I see that almost all of your posts were made 4 years ago Nick and so I have to ask; your 'no-liquid-water' "white Mars" liquid CO2 only theory, if it hasn't been well and truly demolished by the findings of the MER's over the past several years must be hanging by the thinnest, most gossamer thread imaginable. Are you prepared to abandon it as the evidence now appears to demand that you must?
gallen_53
QUOTE (nprev @ Jun 4 2008, 06:33 PM) *
Or electrostatically clingy? Just a thought; water really is practically a mineral where Phoenix is.


An electrostatic clinging mechanism would be my guess as well.

I suggest that the guys at JPL smear a regolith sample flat on a metal surface of the vehicle and let it sun a bit. Then scrape it up and deposit it into the TEGA.

Another approach would be to scoop up some regolith, jiggle the sample, orient the scoop so the sample gets lots of sunlight, jiggle some more, repeat several times and then deposit the sample into the TEGA.

The trick is to encourage electrostatic discharge. Short wavelength UV reaches the Martian surface and that should accelerate electrostatic discharge if the sample is properly exposed.
ngunn
Excellent replies from the chemists as I had hoped. I've no objection to the electrostatic-sticky explanation, but nevertheless I persist with the thought that there could be a damp-sticky component (possibly a seasonal transient one) in this soil. Abandoning foolhardy attempts to guess myself what that might possibly be I ask the experts again this wider question. Are there any plausible candidates?
Tman
Could it be that the behavior of this sample is affected by the soil that was blown away (and probably melted too) when Phoenix landed?
Aussie
QUOTE (gallen_53 @ Jun 8 2008, 07:02 AM) *
An electrostatic clinging mechanism would be my guess as well...... Short wavelength UV reaches the Martian surface and that should accelerate electrostatic discharge if the sample is properly exposed.


But the dust deposited on the MER solar panels clumps? So perhaps the electrostatic explanation is not the answer. I think ngunn has asked an extremely valid question. Is there a cementation process here and if so what?
SickNick
QUOTE (Aussie @ Jun 8 2008, 07:05 PM) *
But the dust deposited on the MER solar panels clumps? So perhaps the electrostatic explanation is not the answer. I think ngunn has asked an extremely valid question. Is there a cementation process here and if so what?


I don't think there is a "need" for an electrostatic clumping mechanism. The Mars soil is basically rock flour, and extremely fine gained powders (or powders with a fine component) are notorious for clumping. Perhaps it is caused by Van-der-Waals forces between exposed and damaged mineral surfaces in the very fine grains, but it is a genuine and relatively common behaviour. Wheat flour behaves just like this, even though it is compositionally very different.

How to deal with it? More difficult. A small mechanical pulveriser? A forced seive? None of these are built into the TEGA design. Maybe the soil sample can be pushed against the filter grid by the remote arm, but maybe that would just pack it worse?

Maybe the next sample can be dumped from higher up so that it gets more dispersed as it falls? SOme more dump-and-drop trials would be in order, I think. with careful photos of the clumping as the regolith falls/arrives.

maybe the sample needs to be smaller?

Time for some careful trial and error, and some practice with an appropriate physical simulant on Earth...
Zvezdichko
Hello, I have a question which may sounds a bit silly, but anyway. At Uni we study that a soil is a substance which has three components: the mineral component (it's basically the underlying rock), the organic component (humus, peptones and so on), and gas component (CO2, nitrogen...). The Martian soil is obviously lacking the organic component (if Gas-Chromatograph aboard Vikings gave correct results). We are still waiting the results from the problematic TEGA which has some advances (slow heating etc). So why call it "soil"? In the Eastern block we call it just "grunt".
djellison
QUOTE (Zvezdichko @ Jun 8 2008, 10:37 AM) *
So why call it "soil"?


Because that's the lazy thing to call it. Fines, regolith, whatever geologically accurate term you elect to use is fine - but 'common' english means that soil is the 'stuff' on the ground. It's a point that has been at some of the press confs.
Zvezdichko
Once again, thank you, Doug. In the end MECA and TEGA may prove that the Martian soil is more Earth-like, with nearly neutral pH, organic material and normal concentration of salts.
SickNick
QUOTE (Zvezdichko @ Jun 8 2008, 08:38 PM) *
Once again, thank you, Doug. In the end MECA and TEGA may prove that the Martian soil is more Earth-like, with nearly neutral pH, organic material and normal concentration of salts.


let's see what it *does* prove, rather than pushing our own speculative agendas.

The important thing with planetary missions is to wait.

See all the data, and think what the hell it means. It's never what we expected, or imagined, or hoped. Sometimes a single image or data point is a breakthrough. other times it takes an accumulation of images and data to help us understand what's going on.

I'm itching for TEGA data. Let's all try to be patient while our good friends on the mission team work out how to get the data, despite any obstacles that may arise.
Zvezdichko
I apologise to you then. This was my natural desire, my expectations, my heart is with that mission.
glennwsmith
A tip o' the hat to bgarlick for his prediction, on June 4, re difficulty of getting material through the screen. Interesting, that much of the challenge of space exploration will involve what could be referred to as "fuzzy" engineering, ie, the problem of lunar dust. But the Phoenix team has a lot of options, and they will figure it out!
Sputnik
Wouldn't a high frequency vibrator between the bottom of the receptacle and the oven itself be enough to shake some particles from the sample, into the oven?
gallen_53
QUOTE (SickNick @ Jun 8 2008, 09:18 AM) *
IMaybe the next sample can be dumped from higher up so that it gets more dispersed as it falls? SOme more dump-and-drop trials would be in order, I think. with careful photos of the clumping as the regolith falls/arrives.


That's the ticket! Just slowly pour it in from higher up. It'll be a bit messy but should do the trick.
gallen_53
Sushil Atreya (a professor at the University of Michigan) has written some papers about the accumulation of electrostatic charge on Martian dust. This publications list at http://www-personal.umich.edu/~atreya/s_publications.html by Prof. Atreya covers many diverse topics in planetary science, provides PDF links and is very interesting. I suspect Prof. Atreya would have predicted this clumping problem if anyone had bothered to ask him.
JRehling
QUOTE (Tman @ Jun 8 2008, 02:03 AM) *
Could it be that the behavior of this sample is affected by the soil that was blown away (and probably melted too) when Phoenix landed?


There was definitely some alteration of the surface -- the key answer would be, what is the displacement of native surface material as a function of distance from Ground Zero? We can make 3D micro-topo maps of the vicinity and, with the sound assumption that there was nothing special about the landing site before Phoenix dropped out of the sky, measure the local effect. It seems to be something like 6 cm of displacement at Ground Zero. The stain shown by MRO probably corresponds to the boundary of a VERY slight alteration of the surface (akin to dust devil tracks or less -- the backshell made a stain a significant fraction of the same size).

I suspect that the alteration where the arm dug first is on millimeter scales and moreover consisted largely of removal of dust rather than alteration of the stuff that's left.

By definition, the post-landing surface consists of the surface where the force of the engines was too weak to move any more material. So I think if the material's failing to fall through the only difference owing to the engines is that there might have been a VERY fine layer of dust that would have fallen through and was instead blown away. If this stuff that was collected had been powdery before, it would have blown away, too.

I highly doubt that the stuff here was melted by the rockets. It takes an awful lot of heat to get that cold of ice up to 0C and much more to melt it. The moment of landing was pretty quick, and exhaust would cool off incredibly fast in that environment.
Sunspot
Has there been any update on the TEGA problem?
akuo
Twitter says:
QUOTE
Goal Sunday was to shake the screen to help soil particles fall into the TEGA oven. Downlinking data o'nite for team to see the result.
Stu
Hey, Doug, if all else fails, they could always ask Lewis Hamilton to give Phoenix a gentle nudge... wink.gif
djellison
You think you're funny... you THINK you're funny.

Actually - that is kind of funny. Hamilton could nudge it one way, Rosberg the other smile.gif
jmknapp
QUOTE (JRehling @ Jun 8 2008, 07:28 PM) *
I highly doubt that the stuff here was melted by the rockets. It takes an awful lot of heat to get that cold of ice up to 0C and much more to melt it. The moment of landing was pretty quick, and exhaust would cool off incredibly fast in that environment.


The ice could sublimate though, right? Phoenix landed around 5pm local time so the temperature probably would have been near the max -30C.

A paper On the sublimation of ice particles on the surface of Mars states:

QUOTE
During the Phoenix mission to Mars it is planned that a Robotic
Arm will be used to obtain samples of sub-surface ice
and deliver these to analysis instruments. The process may take
several hours and there is a concern that, if the samples are not
treated appropriately, significant sublimation could take place.
Cloud physics modelling of sublimation from a single ice
particle suggests that the half-life of 1-mm-diameter particles,
even with no ventilation or solar radiation, would be less than
3 h, even at 223 K [-50C] and that smaller particles or warmer temperatures
would exacerbate the problem. Mars chamber experiments
with isolated particles freely exposed on a surface confirmed
this prediction. The procedure in Phoenix will however be to
collect a small pile of a mixture of ice chips and dust. We find
that the sublimation rate from this will be lower, especially if
the pile is a mix of ice and dust and can be kept cold and shaded.

...

(1) Single small ice particles, or loosely scattered particles are
liable to sublimate rapidly in the atmospheric conditions
anticipated during the Phoenix mission.
(2) When collected together in a pile, the sublimation rate appears
to depend primarily on surface area rather than total
mass. ...
(3) Temperature is THE critical parameter and ice samples collected
during the Phoenix mission must be kept as cold as
possible, and in the shade, while awaiting analysis.
(4) Mixtures of ice particles and dust sublimate less rapidly
than pure ice at the same temperature and in a similar container.
The lowest sublimation rates at temperatures near
−30 ◦C (CSIL, Run 14) occurred for mixtures of ice particles
with very fine dust.
(5) Actual sublimation rates on Mars may be significantly
larger in the presence of wind speeds that exceed a few meters
per second.
MahFL
QUOTE (akuo @ Jun 9 2008, 11:51 AM) *
I'd be surprised if there wasn't a sample acquired now :-)


I am not convinced myself.

Also the next set of doors are well covered in dirt, as the first set did not open correctly with out anything ontop of them it does not bode well for the future. I wonder if the team had tested this situation out, I'd be astonished if they had not.

ugordan
Hmmm... I wonder how much (if any) of the soil fell through the mesh as opposed to just consolidating and sliding downward along the mesh? It doesn't look like the soil level was depressed after the vibration, at least not noticeably. The images don't look very promising to me. Hopefully some of the smaller grains did manage to get through...

MahFL
I still maintain they poured way too much soil onto that oven opening.
Stu
I can't make out much "settling" or shifting either... fingers crossed that some small grains managed to sift out of the underlying crud...

I was very surprised to learn just how tiny these TEGA ovens actually are! There's a good YouTube clip here, and you can see the ovens at 6:23. Tiny!!

Click to view attachment
ugordan
On the brighter side, even if there was soil deposited into the oven, that small an amount wouldn't be readily obvious to the RAC. Fingers crossed.
centsworth_II
I wonder why they started with the uppermost oven. If they had started at the bottom, excess dirt would fall away from the yet unused oven doors. As it is, if they continue from high to low, there will be quite a pile built up by the time they get to the lowest.

.... or, is the TEGA shuttered cover horizontal and only looks tilted in the image?
djellison
The ovens are side by side, not one above the other. That oven is the same level as the other 3 on that side, and the four on this side.

Doug
centsworth_II
QUOTE (djellison @ Jun 9 2008, 09:23 AM) *
The ovens are side by side, not one above the other.

Ah, now ugordan's movie makes sense to me! smile.gif

(I forgot, the shape is like a gable roof.)
djellison
Yeah - it's a very very expensive, but small, barn conversion smile.gif

http://phoenix.lpl.arizona.edu/images/gallery/lg_99.jpg
centsworth_II
QUOTE (djellison @ Jun 9 2008, 09:32 AM) *
Yeah - it's a very very expensive, but small, barn conversion smile.gif

It's funny seeing that salt shaker to the right in the image you link. For depositing test samples? I can't imagine the test bench doubles as a lunch room counter!
tuvas
Poor TEGA... It just doesn't seem to be working quite as intended... I sure hope they can get all of the problems resolved...
centsworth_II
QUOTE (tuvas @ Jun 9 2008, 10:03 AM) *
Poor TEGA... It just doesn't seem to be working quite as intended... I sure hope they can get all of the problems resolved...

I hope you're not saying this based on something you've heard about the second attempt to get sample into the oven.
MahFL
QUOTE (djellison @ Jun 9 2008, 03:32 PM) *
Yeah - it's a very very expensive, but small, barn conversion smile.gif

http://phoenix.lpl.arizona.edu/images/gallery/lg_99.jpg


Hey did ya'll notice the salt shaker in that picture ?
Stu
QUOTE (centsworth_II @ Jun 9 2008, 04:07 PM) *
I hope you're not saying this based on something you've heard about the second attempt to get sample into the oven.


Oh surely not. I can't imagine anyone here who'd be so cruel as to drop a hint about a development they've heard about but can't share with the world yet -

Oh hello Jason, didn't see you there...! wink.gif laugh.gif
jmknapp
Is a press conference scheduled today? Seems like there's a lot of fodder for questions, given that TEGA is kind of the central instrument of this mission, such that "Poor TEGA" = "Poor Phoenix."
Stu
Yep...

Media Update
NASA and the University of Arizona, Tucson, will hold a media teleconference at 11 a.m. PDT (2 p.m. EDT) on Monday, June 9, to report on the latest news from NASA's Phoenix Mars Lander mission.

Sunspot
How many of the original science objectives can be met without TEGA?
ugordan
Whoa, people... Getting a bit negative, aren't we?
Stu
I was just thinking that... come on guys, first sample dump, first oven, first everything. That's why there are more than one on there; it was very unlikely everything would go perfectly the first time. I reckon the Phoenix team reading this need our support and encouragement now. Keep at it! smile.gif

Edit: interesting article here...
MahFL
There are plenty of positive things about Phoenix of course. We have colour and 3d pics of the northern tundra. Pretty sure we see ice under the lander. Temperatures, pressures and wind direction. Microscope views of the dust/dirt. I am sure I missed a few things too.
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