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ExoMars
djellison
post Aug 10 2019, 01:50 PM
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This is a second, separate failure.
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Decepticon
post Aug 10 2019, 05:43 PM
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Is this failure identical to curiosity testing parachute failures?
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mcaplinger
post Aug 10 2019, 06:09 PM
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QUOTE (Decepticon @ Aug 10 2019, 09:43 AM) *
Is this failure identical to curiosity testing parachute failures?

AFAIK, there's no information yet about this most recent failure, and only a little about the problems in May: https://www.esa.int/Our_Activities/Human_an..._and_challenges

QUOTE
The main parachute lid release mechanism worked and the first main parachute also inflated well, but several radial tears in the fabric were observed immediately following extraction from the main parachute bag, before the parachute experienced maximum load.

The second pyrotechnic mortar also worked normally, ejecting the second pilot chute, which also inflated as expected. The second main parachute was extracted from its bag, but one radial tear was observed, again before reaching peak inflation loads.


Why the Exomars EDL system needs four separate parachutes when MSL/M2020 only needs one I don't know.

To oversimplify, parachute failures come in two flavors: the parachute fabric tears (sometimes catastrophically), or the parachute fails to inflate ("squidding"). I seem to recall both types of failure in MSL testing, but I don't recall for sure at the moment.


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djellison
post Aug 11 2019, 06:30 AM
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I think the complexity comes from the fact that neither ESA nor RSA have flown a successful very large Martian 'chute before, so I can understand the desire to 'stage' them with something small and tough, followed by something larger that doesn't have to be strong enough to handle the supersonic deployment. The LDSD deployment used that balute first as a drogue, to then pull out the main (but had two failures of the mains)

I'm at a loss as to how they got to the Drogue-1st Stage Main-Drogue 2-2nd Stage Main four chute design. I'm sure they're not doing it for fun.

The ExoMars EDM had a Disk-Gap-Band canopy of 12m.....but they're not re-using that flight proven design at all (it would make sense as a 1st Stage Main chute - instead they've developed a new 15m chute)

The final Rover EDL chute is for some reason, 35m across. That's more than 50% larger than the MSL 19.7m parachute despite being a lighter entry vehicle.

This was a concern I had about the EDM being so close to the rover mission....there simply isn't the time to take the lessons learned from EDM and then apply those to the design of the rover EDL.
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Phil Stooke
post Aug 11 2019, 06:33 PM
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There was an excellent documentary on the MER project which followed Steve Squyres as the mission developed. I forget its name now. But I recall him saying parachutes were a 'black art' or words to that effect, not really understood as well as you would expect. The inflation process must be a bit chaotic.

Phil


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nprev
post Aug 11 2019, 10:27 PM
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Is parachute design covered at all under ITAR? I have no idea. If not, then I do hope that ESA consults JPL for their decades of experience in this black art.


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djellison
post Aug 11 2019, 11:21 PM
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Certainly at risk of being covered under ITAR/EAR...... a cursory google brings up this which repeatedly cites parachutes as controlled
https://www.bis.doc.gov/index.php/documents...340-ccl9-4/file
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mcaplinger
post Aug 11 2019, 11:55 PM
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QUOTE (nprev @ Aug 11 2019, 02:27 PM) *
...I do hope that ESA consults JPL for their decades of experience in this black art.

As I mentioned upthread, even if there weren't export controls it's unclear if ESA would ask or JPL would respond in detail if they did.

There's a certain amount of open-literature info about US Mars parachute development from Viking on. All the failures on LDSD indicate that there are limits to our knowledge on this, though all the ASPIRE testing makes one feel pretty confident in the MSL parachute design.


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rlorenz
post Aug 12 2019, 07:59 AM
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QUOTE (djellison @ Aug 11 2019, 01:30 AM) *
I'm at a loss as to how they got to the Drogue-1st Stage Main-Drogue 2-2nd Stage Main four chute design. I'm sure they're not doing it for fun.


I had the same reaction - in a comment at IPPW I described this design as 'baroque'. Introducing an extra serial step introduces another failure point - the tradeoff presumably being the ability to nudge all of the elements in the chain further from operating environments (Mach, q, Re etc.) in which they are known to fail.....
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djellison
post Aug 12 2019, 01:47 PM
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“Furthermore, in addition to the regular forum of exchanges between ESA and NASA experts, a workshop of Mars parachute specialists will convene next month to share knowledge.”

http://www.esa.int/Our_Activities/Human_an...sting_continues

Details of multiple recent test failures. But also good news on some info exchange between agencies.
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hendric
post Aug 12 2019, 08:56 PM
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The landing site altitude is about 1400-1600m higher up than Curiosity, with a bit of variation across the ellipse. I did some math with https://www.grc.nasa.gov/WWW/K-12/airplane/atmosmrm.html and that means about 10% less air density.

Maybe there are lower descent speed requirements on their landing site acquisition?


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vikingmars
post Aug 13 2019, 08:23 AM
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Thanks for the link to the ESA page : I discovered this EDL procedure which seems quite 'baroque' to me also, with all those parachutes sequences embedded in one another.
Many failure points are at risk and I would have liked Jim Martin (Viking Program Manager) to give us his opinion on the subject.
Then... let's go back to the basics ...which are still to be considered as a technological feat even 43 years after the successful landings of the two Viking spacecrafts !
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