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

[Guest_Zvezdichko_*]

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?

[rlorenz]

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.

[Skyrunner]

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.

[rlorenz]

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.

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

[Skyrunner]

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.

[climber]

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

[mars loon]

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

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

[BrianL]

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

Brian

[bgarlick]

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...

[Airbag]

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

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

[rlorenz]

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).
......
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...?

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.

[Sandro]

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

[MahFL]

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

[djellison]

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

Doug

[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?