Hello,

According to the publication here:
http://www.space.com/missionlaunches/08053...ion-update.html


The glitch seems to be a short circuit in a filament in a part of the instrument that ionizes the vapors before they are sent to the detector...

Does that mean that it's directly related to the DSC oven?

Doesnt sound like it. Remember each oven has its own heater and sense windings. This sounds like the filiament
to generate electrons to ionise the evolved gases before they pass into the quadrupole (i.e. part of the mass
spectrometer - the EGA part of TEGA)

Hopefully as the release says, they can get it up and running nonetheless. But even if the mass spec croaks
altogether there is a good chance of detecting water ice in the TA (thermal analyser, aka DSC - actually there
is a whole literature on how to run these things, whether it is a Differential Thermal Analyzer or a Differential
Scanning Calorimeter is largely an issue of software). Either way, you can detect the latent heat of melting
and evaporation.

As I understand it the part that has shorted out is one of the two carrier gas ionizers.

The ovens vaporize the soil samples; these vapors are carried by a neutral carrier gas to the mass spectrometer. But before the carrier gas is fed over the sample it is charged then accelerated. The ionizer is needed to charge the gas so it can be be accelerated (like in an ion engine). Luckily there are two coils so when one is malfunctioning the other may be used instead. It seems to me that the team has some confidence that this is the case and full functionality can be restored.

No. ionization occurs in the mass spec. The carrier gas is neutral - remember the baking in the
ovens must be done under 'pressure'.

Yeah, I should have known that. Next time I work with the gas chromatograph mass spectrometer we have at the faculty I shall pay more attention to the explanations of the lab technician.

As hoped it is working with the backup ionizing filament now.

One TEGA image on sol 9 : http://phoenix.lpl.arizona.edu/images.php?...2662&cID=40
Looks like "something" is open now


Edit : labbeled Sol 9 but from sol 8

At todays (June 3) telecon, Peter discussed this. One door is fully open. The other is visibly and "unexpectedly" not fully open. they are working on it.

ken

Are they planning to test all the doors to see if any more might have issues?

Brian

Do the doors need to also be able to close for proper TEGA functioning?
If not, I imagine the doors could be forced fully open by using a corner of the scoop if need be...

I can't imagine so as then they would lose the ability to control what sample goes in what container - assuming the doors can not be closed again, or at least risking a door not being closed again.

Which brings up a point - can the TEGA doors also be closed again? The TEGA documentation I have read only mentions that the doors are solenoid operated, but does not say they are/can be closed prior to TEGA thermal analysis (which is not necessary since each oven seals itself).

Let's say the doors can close - but would the dirt that was not filtered through and vibrated off the screen not prevent them from doing so anyway?

But say they can not close - then could a misplaced clump of dirt not prevent the neighboring door from opening, if said clump of Mars' finest dirt was deposited along the hinges of two adjoining doors, especially if one of those doors was at a convenient angle for the dirt to slide down towards the hinge...?

Well, we'll see soon enough!

Airbag

IIRC the doors are spring-loaded, and *released* by solenoid. No closure possible. (Opening is inhibited
by a memory-metal clutch thingy to prevent launch vibration popping it open)

Obviously, as you say, door closure is not needed for the analysis, as the oven seal takes care of isolating
the sample from the atmosphere.

As for dirt - it would need an awful lot of dirt to jam up an adjacent door. Getting enough sample is
considered more of a concern than getting too much.

Hi together

I just had an short idea on a possible fix for the not fully open door. Although they can operate with the door not fully open (as far as I understood) I think it could be possible to open the door with help of the robot arm.

The doors are spring loaded and if they would move the arm slightly from left to the right (on this picture http://phoenix.lpl.arizona.edu/images.php?...2662&cID=40 ) over the not fully open door, we could press the door again down and hope that after the pass of the arm the springs will push the door fully open.

What are your thoughts about that option?

Regards,
Sandro

I think the safest thing to do is just use the oven as it is, as they say the door is open enough.

A thermal day-night cycle may well help it deploy further as well. But active intervention would be un-necessary

Doug

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?

Whenever something gets stuck on a spacecraft, the two options available seem to be (1) jiggle it and (2) heat it. I'm imagining a spacecraft with lots of little peizoelectric-cum-resisting pads that can just vibrate and heat lots of things all over the spacecraft. This is an evolution from an earlier plan whereby each orbiter would have a micro helperbot that was equipped with (1) a hammer.

I think they would have thought about this before they launched it..........

Note that they did do a second dig-n-dump because they were caught off guard by how sticky/clumpy the first scoop was.
Maybe the soil's properties are not exactly what they were expecting...

Or electrostatically clingy? Just a thought; water really is practically a mineral where Phoenix is.

I'm still kind of surprised that they did not use up one of the TEGA ovens for a "contingency" sample. On the Apollo missions that is pretty much the first thing they did on the first EVA of each mission - take a contingency sample of soil and rocks right outside the LEM, whatever was there. Then at least in case some emergency arises you have *some* samples.

If I were in charge I'd have dumped that very first scoop into a TEGA oven. Still have 7 ovens left, which is more than MECA can handle anyway, and what if the RA suddenly stops working...?

Airbag

What a relative of mine, an engineer, likes to refer to as "the instrument of persuasion."

TTT

On the other hand, what if the first use of the RA were the event that made it fail and we did so retrieving an uninteresting sample instead of an interesting one. Risk is a complex thing.

I like Sandro's idea, after it has had time to open on its own.

There is an actuator that vibrates the funnel to encourage material to flow down into the oven. You could think
of it as a hammer...

I wonder if that vibration extends to the screen, encouraging loosely clumped material to break up and fall through.

That may be, but from many reports it seems that it is the daily temperature variations that are the main source of unexpected component failures. So the longer you wait before doing something, the bigger the chance something will break.

Airbag

Not in as quantitative a way as one would want (it isnt a ThermoGravimetric Analyser)

There is an LED/photodiode 'oven full indicator' that shows if soil has backed up in
the load pipe - typically because the oven is full (duh). Transient signals from that may
give an indication of stuff drizzling into the oven during loading before it gets full.

A minor role I have associated with the TEGA team (I worked on TEGA-1 on MPL) on
which I did some lab testing while still in Arizona is on seeing whether the photodiode
data can give a sample mass estimate.

ans : maybe.

(a post-hoc mass estimate can also be had from the DSC data which indicates the heat capacity of the
sample, but that is also somewhat sample-dependent)

Ironically, it is a "hammer" that appears to be causing the filament problem, and which could also be used as an "instrument of persuasion" in extremis.

There is a solenoid on the atmospheric gas inlet valve that gives a hefty kick when it opens and closes. The short-circuit apparently comes and goes with the operation of this valve. If the back-up filament were to fail, the fall-back would be to operate the inlet valve until the circuit closes on the primary unit and then leave it. Right now, I believe they're not operating the inlet valve - IIRC they are content to sample the atmosphere by opening the cell door, which is less optimal than venting through a small valve.

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.

Wasn't this a concern for Viking as well?

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"

Mythbusters
"With enough lubrication, we can do anything"



Doug

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.

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

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

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."

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!

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.

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

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

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


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

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.

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 !

Oh oh, lots of head scratching at UA.

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? )

Here is where litter box skills will come in handy. Yes, this may a job for Steve the Cat!!!!

Seriously.... I believe there were similar issues on Viking, and that team worked it through. I am sure this team can do the same.

Does anyone know if the scoop arm is capable of actually touching the TEGA ports? I am not sure if it can reach down that far.

Craig

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 liquid phase of CO2 is forbidden below 5 bar.

That's a very good start! But I need more to dismiss the idea entirely. We don't know what chemical games CO2 engages in when it is a constituent of the soil.

I suppose we also have to consider aqueous brines with excessively low melting points for the cause of the stickiness. Is there such a thing as a H2O:CO2:chloride brine?

Ionic salts are insoluble in liquid CO2 because it's non-polar and the solubility of CO2 in water at low pressure is insufficient to have an appreciable freezing point depression effect.