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What happened?



 
 
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  #11  
Old October 24th 16, 12:06 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default What happened?

JF Mezei wrote:


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" ?


Aerodynamics - get some.


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.


Where do you think the craft gets its vertical descent speed from?

IMUs can only measure accelerations.


--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson
  #12  
Old November 28th 16, 12:06 AM posted to sci.space.policy
jacob navia
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Posts: 341
Default What happened?

Le 22/10/2016 Ã* 22:54, jacob navia a écrit :
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.


This is being confirmed by the french journal "liberation" today.
The inertial altimetre that took the relay from the radar altimetre got
"saturated" and stayed at its maximum value for a second. That led to
the crash. The computer received a negatiuve measure (it thought it was
under the soil) and started the soil sequence at 3 Km over the real
martian soil.
  #13  
Old November 30th 16, 12:18 AM posted to sci.space.policy
William Mook[_2_]
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Posts: 3,840
Default What happened?

On Tuesday, October 25, 2016 at 12:06:31 AM UTC+13, Fred J. McCall wrote:
JF Mezei wrote:


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" ?


Aerodynamics - get some.


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.


Where do you think the craft gets its vertical descent speed from?

IMUs can only measure accelerations.



http://web.mit.edu/digitalapollo/Doc...progreport.pdf

https://www.youtube.com/watch?v=vFv-B_2OV0s

https://www.youtube.com/watch?v=YIBhPsyYCiM

https://www.youtube.com/watch?v=4Vf6Y98ZjwQ

https://www.youtube.com/watch?v=kKIBGY2zaQg

A famous user of an IMU system to travel from Earth to Moon speaks about a primitive guidance system
https://www.youtube.com/watch?v=FD0jUvcMoD4

https://www.youtube.com/watch?v=xQ1O0XR_cA0




--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson

  #14  
Old December 24th 16, 03:35 AM posted to sci.space.policy
William Mook[_2_]
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Posts: 3,840
Default What happened?

On Sunday, October 23, 2016 at 9:54:03 AM UTC+13, 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.


That's why airliners have multiple altimeters on board.

http://www.pmflight.co.uk/wp-content...deck_panel.jpg

The pilot and co-pilot have separate altimeters and rate of climb indicators. The digital flight system has two separate radar based altimeter and rate of climb indicators on the CRTs, and the guidance computer has a separate altitude readout that can also be set to show vertical speed at the press of a button.

 




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