ExoMars - Schiaparelli landing Options

[Gerald]

First, one needs to know the exact chemical. According to this ESA site, the propellant has likely been MMH (monomethylhydrazine), and "MON" as oxidizer, a mix of nitrogen oxides.
According to table 11 of this paper, MMH has a boiling point of about 260 K near 600 Pa. The freezing point of MMH is near 220 K, but it can stay liquid down to 207 K.
Hence MMH may freeze overnight, but evaporate away over daytime, unless it isn't decomposed on impact.

If the impact didn't cause immediate decomposition, it's likely, that the presence of MON formed a hypergolic mix with MMH, resulting in an explosion, and consecutive decomposition of the remaining MMH.

[mcaplinger]

According to this ESA site, the propellant has likely been MMH (monomethylhydrazine), and "MON" as oxidizer, a mix of nitrogen oxides.

No, the lander was a monoprop system using only hydrazine (N2H4). http://spaceflight101.com/exomars/schiaparelli-edm/

Same thing with MSL.

I wasn't able to find the phase diagram of hydrazine, but I would expect most of it to have evaporated under martian ambient pressure.

[Gerald]

I should have remembered that from a few days before...
If it's really pure hydrazine with no water content, it freezes near 2 C.
According to this article, the vapor pressure of solid hydrazine at 0 C is 2.60 mm Hg or 2.60 hPa x 1013.25 / 760 = 3.47 hPa. Therefore at estimated 6 hPa on Mars, there should be a narrow temperature range, where hydrazine would be an oily liquid.
But due to the zero partial hydrazine pressure on Mars, it will boil, then evaporate until it freezes, then sublimate.

But again, it is likely to decompose in an explosion on impact:

Hydrazine is listed among shock-sensitive chemicals, as a chemical prone to rapidly decompose or explode when struck, vibrated, or otherwise agitated.

Or on contact with the surface material on Mars, especially with the iron oxides bearing dust:

Hydrazine spontaneously explodes upon contact with calcium oxide, barium oxide, iron oxides, copper oxide, chromate salts, and many others.

This may be dependent of the temperature, but it's reasonable to assume, that the hydrazine in the tanks was warmed and liquid on impact.

If the hydrazine contains some stabilizing additive, odds for staying stable on impact might be a little better. But it will nevertheless react or decompose in the Martian environment after days or weeks.

[HSchirmer]

there was a timeout in the radar altimeter that ultimately made the onboard computer think it was on the ground far too early.

Just noticed an interesting quote-

from the Mars Climate Sounder, we have observed Mars' semidiurnal tide.
These waves can cause large variations in atmospheric density in regions
where engineers would typically rely on atmospheric braking to slow down vehicles.

And a prior article about a 170-120 Kelvin difference because of the tides.
http://www.planetary.org/blogs/guest-blogs...atmosphere.html

Now, that's a twist I had not thought of. Without running through pv=nrt,
a difference of 50 kelvin degrees, at 120 degrees kelvin, is a huge change in pressure.

Just like a homerun baseball travels farther through thin summer air, shorter through dense fall air,
perhaps part of the story here is that Mars' atmosphere has some major density fluctuations?

[mcaplinger]

perhaps part of the story here is that Mars' atmosphere has some major density fluctuations?

That's always been a fact of life for EDL. It doesn't look to me like it affects the terminal part of landing, it mostly means that the time spent on parachute can vary by a significant amount. It's basically why you need the radar, you can't rely on absolute pressure sensing to figure out your altitude relative to the ground.

[Explorer1]

Colour HiRISE imagery released: http://www.esa.int/Our_Activities/Space_Sc..._site_in_colour
http://www.uahirise.org/releases/esa-edm/second-image.php

The white spots are real objects, parachute moving in the wind...

[nogal]

Here is a refreshed version of the Schiaparelli KML file for GE. I added several ground overlays with the recently released HiRISE color and black & white images. Do zoom in to see them. All images can individualy be made visible or hidden.

There are many white dots around the crash crater, which are interpreted as pieces that broke off Schiaparelli.
Rapidly toggle on and off the color image of the parachute to see it flip (interpreted as caused by wind, just as MSL's parachute).

The HiRISE b&w image's size is 6.82MB, so the KML directly loads it from the ESA web site (instead of being included in the KMZ). This takes a little time and requires the user to be online.

Fernando
 Schiaparelli.kmz ( 602.11K ) Number of downloads: 334

[PDP8E]

Here is the HiRise color image of the Schiaparelli Impact site.
4X and de-convoluted
My thoughts:
* the three big white spots are the three main fuel tanks for the retrorockets
* the arcing line off the right is the pressurized helium tank, spewing (its purpose was to to pressurize the the fuel tanks as each emptied)
* as always ... your mileage may vary

[PDP8E]

ESA says in the article cited below, that the investigation should be done by the end of November. The fuzzy 'software glitch' starts to comes into more focus:

"Fundamentally there’s a software issue here between the radar and the on-board computer system,” Mark McCaughrean, a senior science advisor at ESA, told the Associated Press. “The radar was giving inconsistent info on where it was.”

http://www.csmonitor.com/Science/2016/1105...sh-site-tell-us

[marsophile]

Similar information in this new BBC report:

http://www.bbc.com/news/science-environment-37898565

"The onboard computer had some problems taking data from different sources, and defining correctly the altitude...."

[nogal]

Here is an interesting article from ESA on a new microprocessor for space applications.
http://www.esa.int/Our_Activities/Space_En...issions_smarter
Interesting to note that the radiation hardening process, despite progresses, still results in larger circuitry (65 nm) and much smaller speeds (250 MHz) as compared to non-space qualified microprocessors (e.g. the z13 at 22nm and 5GHz).
Fernando

[PDP8E]

The Italian news agencies are running several stories today about the Schiaparelli EDM Lander.
I counted six articles -- all roughly the same
The craft was built in Italy for ESA. Thales Alenia Space is the spacecraft builder in coordination with Russia’s Roscosmos. The official ESA (interim?) crash report is due on November 24, 2016

Enrico Flamini, 'scientific coordinator' at the Italian Space Agency (ASI) relates what went wrong with the Schiaparelli EDM lander.
• He reports that the lander was ‘in wild oscillation’ on the parachute
• When the altimeter read 2000 meters, the gyros reported -10m (below the surface)
• He said the computer believed the gyros and eventually the lander crashed
• He also said that the stratospheric balloon drop tests of the whole system were never done, to save a million euros
• ASI wanted the Swedish Space Corporation to do the ‘stratospheric throws’, but ESA gave the work to a Romanian company that eventually didn’t do the job
• ESA then 'made itself content' with computer simulations of the landing provided by a British company

Here is one (of many links available)

Sciaparelli Crash http://www.quotidiano.net/tech/marte-schiaparelli-sonda-1.2690005

[mcaplinger]

• When the altimeter read 2000 meters, the gyros reported -10m (below the surface)

Gyros don't measure altitude, and as noted upthread, IMUs can't be used to determine absolute height above the ground. So this part of the story makes little sense. Let's just wait for the report and ignore media misunderstandings.

[JRehling]

As noted, this isn't a complete/consistent account. It seems to remain open as to whether software caused the crash or if the software simply responded futilely to an already hopeless situation.

Fluid dynamics are not trivial to model computationally, so using computer simulations to validate parachute descent seems like a bad option, but saying that now benefits, of course, from hindsight.

[mcaplinger]

using computer simulations to validate parachute descent seems like a bad option...

The last time the US did actual flight-like testing of supersonic parachutes was for Viking (not counting the LDSD flights, which both failed.)