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Posted: |
Oct 19, 2016 - 2:37 PM
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By: |
Solium
(Member)
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Well, we're only surmising what may have happened here. The platform was throwaway from the start. It is not powered via a renewable form of energy transfer, such as solar power cell, or anything similar. As you may well know, it was powered by batteries and, therefore, a very limited lifetime is all it would have, anyway. It's whole design is actually totally contrary to the paradigm under which modern spacecraft systems seem to revolve these days - which involves some kind of longevity and the ability to move from place to place.
I heard the lander was designed simply for testing their landing system for future missions, so that makes sense.
Further news:
Schiaparelli's signal came in loud and clear as the lander streaked through the Martian atmosphere but stopped shortly before the lander was scheduled to hit the ground, said Paolo Ferri, head of ESA's mission operations department.
Schiaparelli reached the Red Planet first, hitting the thin Martian atmosphere at the blistering speed of 13,050 mph (21,000 km/h). Mission team members tracked the lander's progress this far, but they weren't able follow it all the way down to the surface.
"It's clear that these are not good signs, but we will need more information, and that's what's going to happen tonight," Ferri said. "I'm quite confident that tomorrow morning we will know" what happened, he added.
http://www.space.com/34451-exomars-mars-arrival-success-landing-uncertainty.html
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Posted: |
Nov 7, 2016 - 10:43 AM
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By: |
Grecchus
(Member)
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The news regarding Schiaparelli's demise is still surging:
http://www.dailymail.co.uk/sciencetech/article-3879580/New-images-crater-created-Mars-European-lander.html
They say the thrusters meant to cushion the lander's soft touchdown only fired for about 3 seconds because it thought it was closer to the surface than it really was. There's only one cause for this, as I see it. The lower heat shield was detached and dropped below the lander still connected to the drag chute harness, which was above it. Now, Schiaparelli has four 'lookdown' radar pingers - one centrally placed and pointing straight down, with three others angled to detect the ground using slant range. If the lander was rotating fairly rapidly, then one or more of the slant ranged radars could have picked up a return from the dropped heat shield on it's way down. The lander might register this as a broad ranged surface beneath, with statistically sampled upland and lowland terrain around an average interval. If this happened, then there was no fail safe routine to restart the landing rockets once they'd shut down. Did the lander have a software check to see if such a case would be considered - did a saturation of radar returns cause a misstep to occur such that it misidentified the lower heat shield for the terrain it was aiming for? Did the landing radar make provision for the jettisoned heat shield being in it's field of view, quite possibly for a lengthy period of time, in which case it would need to have the ability to delineate if from the terrain background and keep track of the relative motion made by it for as long as it remained in the field of view. It would even need to have knowledge of the heat shield relative motion to the extent that the heat shield could enter and exit the field of view intermittently multiple times and that it should not be mistaken for the ground. That's a hard problem to solve!
In the post landing attempt images of Mars' surface that have been published, it is only too clear the wreckage is strewn over a narrow stretch of ground. The initially jettisoned part of the lander could very well have interfered with the lander's ability to 'see' what really was below it. Did the on board computer have a 'Hal-9000' moment? That is to say, could it have made a forced interpretation of one situation for another which, to all intents and purposes, was undefined as far as it was concerned?
Could this 120 degree coverage, by both the landing radars and the rocket landing systems be seriously flawed design concepts in the blinkered way they might have been integrated?
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Posted: |
Nov 28, 2016 - 10:13 AM
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By: |
Grecchus
(Member)
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The IMU on Schiaparelli would have had to have been initialised prior to separation from the TGO.
The TGO will have it's own IMU. I assume Sciaparelli's IMU would have remained dormant and switched off for most of the flight to Mars. The TGO though, like most probes, will need to have some external and automatic method of sighting the stars on the Celestial Sphere, so that any mechanical drift occurring within the unit, and giving rise to errors in position and velocity that may occur from time to time, can be spotted and corrected so the spacecraft can position itself correctly for the time it needs to initiate the firing of it's main rocket engine to allow it to reach it's destination safely. Needless to say, the TGO's IMU would need to remain switched on at all times because IT IS the navigation platform which tells the TGO where it is in space relative to the Sun, Earth, Mars and any other mass of relevance to it's flight - at all times.
There would be some usefulness in keeping Schiaparelli's IMU also turned on for the duration of the flight to Mars. If it is identical in make to the TGO's, then the two platforms can synchronize with one another. Any 'drift' between the two units would provide useful information about their reliability curves whether they are of the same make or not. The IMU is basically a virtual reality machine, just like in a computer game. The only difference is it operates in a real environment in real time. For those who don't have a clue what the IMU does (and that includes me when it comes to exact details), it is basically a gyroscopically stabilised surface which remains rock steady in position with respect to the Celestial Sphere around it no matter where it is located within the Solar system. The Pole Star will always remain in exactly the same relative position to it no matter what the spacecraft it is a part of is doing. It can't flinch an inch. Whenever the spacecraft rotates around it's centre of mass, the IMU also moves in a proportionally countered way, but is gimbaled so that if YOU were the IMU, whenever the spacecraft rotates it would appear that you are remaining perfectly still with respect to ALL the surrounding stars while the spacecraft does the actual rotating around you. For this reason, the IMU is also known as a 'stable element.' Because the IMU is a mechanical device in frictional contact with the rest of the spacecraft through it's gimbals, mechanical friction will, over time, cause the entire frame of the surrounding stars to have shifted from the positions they were originally in when it first started working. This is inevitable after the spacecraft has performed a lot of rotational movements. The way to fix this problem is to 'torque' or forcibly wind the IMU back into a three dimensional positional orientation of special spatial significance that will allow it to once again help perform correct calculations regarding it's position in space. Therefore, all the mathematical operations the TGO's computer performs to calculate it's true position in space, do so from updates that come from the IMU, as well as from strategically placed sensors - called accelerometers - that can very precisely sense the speed the spacecraft attained in the up, down, left, right, forward and backward directions since it first started out on it's journey. So basically, the IMU and it's combined accelerometers allow a spacecraft to robotically 'feel' it's way through space without being a conscious entity. At the same time, it is precisely because it is a robot the IMU can scientifically measure the tiniest movements it makes in space with extreme accuracy that our own senses are unable to quantify in exactitude.
The IMU is like a Swiss made watch whose only function is to tell the time. It is not alive, so it is not conscious of what it does. It does not know that when the short hand points at 12 there is an ambiguity which needs to be resolved. Being an imperfect mechanical device it will run out of clockwork energy and the hour, minute and second hands will eventually start to drift through mechanical friction, and so on. When that happens, a person will have to reset the watch so that it can then reliably tell the time, at least until it once more loses synchronization with the actual time. Well, at least time as defined by us mere mortals. There is always the possibility that even though the watch may very well be giving an accurate display of the actual time, it can still be misread.
What ESA is basically saying is that Schiaparelli's on board timepiece skipped several beats at the most important moment of it's life. We can assume that Schiaparelli's IMU would have been updated directly from the TGO's IMU before they separated. We can also assume that Schiaparelli's IMU could not be updated once it was on it's own, so it's physical state description in space had to be very accurate on it's 3 day coast to Mars, not to mention it's real time 'knowledge' of where Mars' surface would be in relation to itself after entering the planet's atmosphere. If Schiaparelli was spinning at a high rate around it's vertical axis during entry to Mars' atmosphere, the IMU should have been able to cope. When it separated from the TGO it was deliberately imparted with a slow spin for longitudinal stability. This was probably done because Schiaparelli's overall shape was conical, not spherical, and if it did not have any spin to keep it pointing in the right attitude, it could have ended up tumbling due to complex gravitational perturbations that might have moved the forward facing heat shield into a non-forward facing orientation. I find it hard to believe this spin could have increased during entry to Mars' atmosphere. You'd think the atmospheric drag would eventually stop the spin at some point. It's computer must have had a reasonably fast processor that could perform all the concatenated matrix math that is part and parcel of controlled space flight in this day and age. If Schiaparelli was spinning so fast it's IMU couldn't update it's own state vector, then it was in a physical state no one had envisaged. Still, that amazing photographic evidence showing us Schiaparelli's fate also seems to indicate it was still spinning at a phenomenal rate when it hit the ground.
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