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What happened?



 
 
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  #1  
Old October 22nd 16, 09:54 PM posted to sci.space.policy
jacob navia
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Posts: 341
Default What happened?

Altimeter failure. The instrument indicates a much lower altitude than
the real one. So, thinking they are much lower, software ejects the
parachutes, then when the rockets are turned on, the altimeter tells
that they have landed and software shuts down the rockets.

Then it goes from there till the crash at 300Km/h with no parachute and
no rockets...

Single point failure. All mission relies on the altimeter.
  #2  
Old October 22nd 16, 10:11 PM posted to sci.space.policy
Rob[_8_]
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Default What happened?

jacob navia wrote:
Altimeter failure. The instrument indicates a much lower altitude than
the real one. So, thinking they are much lower, software ejects the
parachutes, then when the rockets are turned on, the altimeter tells
that they have landed and software shuts down the rockets.

Then it goes from there till the crash at 300Km/h with no parachute and
no rockets...

Single point failure. All mission relies on the altimeter.


Is this your personal guess or the first outcome of the investigations?
Boeing made that mistake as well... Turkish Airlines 1951
  #3  
Old October 23rd 16, 07:39 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Default What happened?

JF Mezei wrote:

On 2016-10-22 16:54, jacob navia wrote:

Altimeter failure. The instrument indicates a much lower altitude than
the real one. So, thinking they are much lower, software ejects the
parachutes, then when the rockets are turned on, the altimeter tells
that they have landed and software shuts down the rockets.


Pardon my ignorance, but which accident are you refering to ?


I'm sure he's talking about the recent failure of the European Mars
lander.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #5  
Old October 23rd 16, 11:05 PM posted to sci.space.policy
jacob navia
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Posts: 341
Default What happened?

Le 22/10/2016 à 23:11, Rob a écrit :
Boeing made that mistake as well... Turkish Airlines 1951


Yeah, a bug can happen to anyone. Fortunately there wasn't anybody on
board of the esa probe.

Another advantage of the "toasters". Nobody was killed.

  #6  
Old October 23rd 16, 11:06 PM posted to sci.space.policy
jacob navia
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Posts: 341
Default What happened?

Le 23/10/2016 à 08:39, Fred J. McCall a écrit :
JF Mezei wrote:

On 2016-10-22 16:54, jacob navia wrote:

Altimeter failure. The instrument indicates a much lower altitude than
the real one. So, thinking they are much lower, software ejects the
parachutes, then when the rockets are turned on, the altimeter tells
that they have landed and software shuts down the rockets.


Pardon my ignorance, but which accident are you refering to ?


I'm sure he's talking about the recent failure of the European Mars
lander.



Well of course. And all this is just personal speculation since I have
no access to any esa data.

But it looks awfully like that.

  #7  
Old October 23rd 16, 11:08 PM posted to sci.space.policy
jacob navia
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Posts: 341
Default What happened?

Le 23/10/2016 à 15:40, Jeff Findley a écrit :
Seems awfully silly.


All bugs are that: stupid mistakes. ESA was able to land on Titan, and
now they are unable to land on Mars.

Why not copy the opportunity/spirit design?

It was robust and very simple.
  #8  
Old October 23rd 16, 11:15 PM posted to sci.space.policy
jacob navia
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Default What happened?

Le 23/10/2016 à 15:40, Jeff Findley a écrit :
Sounds like a possibly. But designing the thing to have a single point
of failure like this? Seems awfully silly.


If you look he
http://www.esa.int/var/esa/storage/i...images/2016/02
/exomars_2016_schiaparelli_descent_sequence_16_9/15826994-1-eng-GB/ExoMars_2016_Schiaparelli_descent_sequence_16_9.jp g

you see that radar turns on after the heat shield separates.

If that radar sent a wrong altitude to the software... mission was
doomed to failure.

P.S. CAREFUL with the URL being cutted in pieces by the old USENET system.
  #9  
Old October 24th 16, 10:45 AM posted to sci.space.policy
Rob[_8_]
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Posts: 57
Default What happened?

JF Mezei wrote:
On 2016-10-23 18:15, jacob navia wrote:
http://www.esa.int/var/esa/storage/i...images/2016/02

/exomars_2016_schiaparelli_descent_sequence_16_9/15826994-1-eng-GB/ExoMars_2016_Schiaparelli_descent_sequence_16_9.jp g


Sometimes, it has to be "learned".

Airbus had fancy software on its A320 to protect against accidental
deployment of spoilers and thrust reversers. (which had caused some
crashes in the past). It required the nose wheel to spin AND pressure
switch indicating wheight on the wheel.

Problem happened when plane landed during storm, and hyroplaned, so nose
wheel did not spin and pilot unable to deploy spoilers/thrust reversers.
They likely changed the "and" to a "or".


What if the heat shield did not get out of the way and the craft got
within 4m from it, triggering the radar to say "4m altitude, turn off
the thrusters" ?

The "software" solution would have to consider vertical descent speed
"do not turn off thrusters if vertical speed is greater than 4km/h no
matter what altitude you're at". So the shield obstructig radar would
not have caused thrusters to turn off. But as long as hield was in the
way, it would have to use IMU to deduct its vertical speed and be flying
bnlind.


When the radar does not work correctly so there is no correct height
figure available, there probably will be no correct vertical speed
figure either (which is likely derived from the changing height).

In Turkish Airlines 1951 the radar altimeter was defective and indicated
a constant value near zero, which caused the plane to flare and the
engines to go to idle while it was still 300ft in the air.
Curiously there were redundant altimeters (radar and barometric) but
only the value of a single radar altimeter was used for this function
even when it is defective. Clearly a design error.

Redundant hardware also isn't always the solution, especially when it
is identical and running the same software. See Ariane 501.
  #10  
Old October 24th 16, 10:47 AM posted to sci.space.policy
Rob[_8_]
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Posts: 57
Default What happened?

jacob navia wrote:
Le 23/10/2016 Ã* 15:40, Jeff Findley a écrit :
Seems awfully silly.


All bugs are that: stupid mistakes. ESA was able to land on Titan, and
now they are unable to land on Mars.

Why not copy the opportunity/spirit design?

It was robust and very simple.


It looks like this was an attempt to land a device with much higher mass.
It seems like this one was very heavy for what it was intended to do
on the surface, they wanted to experiment for the next mission which
intends to land a much larger rover.
 




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