Launch News Ariane 5 (VA241) : SES-14 (with NASA GOLD payload) & Al Yah-3 : Jan. 25, 2018

boogabooga

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[ame="https://youtu.be/00Kz94aMaCc?t=2413"]LIVE: Ariane 5 Rocket Launches SES-14 & Al Yah-3 Satellites (Flight VA241) - YouTube[/ame]

At 39:54
 
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Thunder Chicken

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I must admit that I don't see any tears..

Me neither.

I really think that the rocket was somehow accidentally programmed to fly that particular trajectory. Everyone seemed to believe that this was a nominal on-trajectory launch throughout, including range safety, which is interesting.

The rocket may have been 100% fine; it was simply told to go into the wrong orbit.
 

GLS

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Independent Enquiry Commission announces conclusions concerning the launcher trajectory deviation during Flight VA241
The Independent Enquiry Commission formed after the Ariane 5 launcher’s trajectory deviation during its January 25, 2018 mission issued its conclusions on Thursday, February 22. The anomaly’s cause is perfectly understood and recommendations are clearly identified. Arianespace and ArianeGroup are immediately implementing the Independent Enquiry Commission’s recommended corrective measures. The current Soyuz and Ariane 5 launch campaigns are continuing at the Guiana Space Center in French Guiana for the two launches planned in March.
http://www.arianespace.com/press-release/independent-enquiry-commission-announces-conclusions-concerning-the-launcher-trajectory-deviation-during-flight-va241/

Given the special requirements of this mission, the azimuth required for the alignment of the inertial units was 70 degrees instead of 90 degrees, as is most often the case for missions to geostationary transfer orbit. This gap led to the 20-degree shift to the south in the launcher trajectory from the initial seconds of flight.
oops... :uhh:
 

Thunder Chicken

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Can someone explain this 70 degree vs 90 degree business? What were these 'special requirements'?
 

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Can someone explain this 70 degree vs 90 degree business? What were these 'special requirements'?

The choice of angle probably has to do with keeping away from gimbal lock during the flight.

During launch guidance says "I want to go in a direction that is 'reference azimuth + (+/-)25º'". But as the reference azimuth had that 20º error (90º instead of 70º, it went further south than expected.

So guidance worked perfectly, it was just following a wrong trajectory. :lol:
 

boogabooga

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Seems uncharacteristically unprofessional on part of Arianespace.

I'm morbidly watching this:
http://www.arianespace.com/careers/

for more positions to open up...

If there are experienced European QA engineers on the forum, might be a good time to update your CV.
 
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Urwumpe

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Except that Ariane launchers can't have a gimbal lock. They have no stable platform. :lol: They use a strap-down navigation system. That is also why it is easy to calibrate it wrong - there is nothing mechanic moving that could give a hint of a wrong alignment.
 

Thunder Chicken

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Except that Ariane launchers can't have a gimbal lock. They have no stable platform. :lol: They use a strap-down navigation system. That is also why it is easy to calibrate it wrong - there is nothing mechanic moving that could give a hint of a wrong alignment.

I'm still missing something - wasn't the initial position state of the rocket entered incorrectly? What about this particular launch caused the 90 degree azimuth to be incorrect? The only thing I can visualize is that the rocket was physically rotated 20 degrees.
 

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So it had a pure inertial guidance system which got deviated by 20 degrees? How common is that? I always assumed that , aside from the pre-programmed trajectory. modern rockets would be "aware" of their position. Perhaps even with calculations as to what corrections would be needed to stay on course.
 

Thunder Chicken

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So it had a pure inertial guidance system which got deviated by 20 degrees? How common is that? I always assumed that , aside from the pre-programmed trajectory. modern rockets would be "aware" of their position. Perhaps even with calculations as to what corrections would be needed to stay on course.

They are "aware" of their position relative to their entered initial state due to their accelerometers.

I'm still struggling to picture where the mistake was made and why it wasn't caught. If it had a strapped down guidance system, and it launched from a known pad with a known orientation, physical mis-rotation of the vehicle seems impossible.

Is it simply that someone typed 70 instead of 90 into the guidance code? That would seem to be a ridiculous error that should have been easy to check with any rudimentary QC.

I'm just struggling with what was incorrect and how was it hidden.
 
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