I remember, shortly after the incident, some people guessing that this had simply been an incorrect azimuth entry. The main argument against this theory was that a 20 degree difference would surely have brought the vehicle outside of the range track quite early on. For a 20 degree difference, every kilometer downrange is another 364 meters away from the expected position at that time, or another 342 meters away from the nominal flight line as the crow flies.
l’origine du problème est une demande inédite d’un des clients pour qu’en fin de mission son satellite soit séparé de l’étage supérieur à angle droit de la trajectoire de vol
Quotel’origine du problème est une demande inédite d’un des clients pour qu’en fin de mission son satellite soit séparé de l’étage supérieur à angle droit de la trajectoire de voltranslation:"the origin of the problem is an unprecedented request from one of the customers so that at the end of mission his satellite be separated from the upper stage at a right angle to the flight path"source: https://www.aerospatium.info/commission-enquete-dedouane-ariane-5/
Quote from: LouScheffer on 02/23/2018 10:19 pmDoes the A5 guidance system have the possibility of gimbal lock?Anything with mechanical gyros has gimbal lock.
Does the A5 guidance system have the possibility of gimbal lock?
Quote from: Craftyatom on 02/23/2018 05:55 pmI remember, shortly after the incident, some people guessing that this had simply been an incorrect azimuth entry. The main argument against this theory was that a 20 degree difference would surely have brought the vehicle outside of the range track quite early on. For a 20 degree difference, every kilometer downrange is another 364 meters away from the expected position at that time, or another 342 meters away from the nominal flight line as the crow flies.I'd still like to see a *real* map of what the allowed flight corridors out of that launch pad (showing what border would/should trigger a destruct), because like Craftyatom I remain unconvinced that there really was such a wide latitude of allowed azimuths. What if it had been 40 degrees off rather than 20? Would they have let it keep going because it was "perfectly healthy"?
incorrect value in specifications for the implementation of the launcher’s two inertial reference systems. 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.
Ariane 5 always used ring laser gyros. No gimbal lock.
most navigation software switched to quaternions long ago, precisely to avoid problem like this. But I'm running out of explanations for why a spacecraft requesting release at right angles to the flight path causes any problem at all.
The IMU is the QUASAR 3000, also used in Ariane 5 and Vega launchers. It provides the GNC algorithms with the IXV attitude quaternion, Euler angles, cumulated angular increments and velocity increments delivered at 100 Hz via 1553 MIL Bus .
Quote from: tvg98 on 02/23/2018 12:43 pmIndependent Enquiry Commission announces conclusions concerning the launcher trajectory deviation during Flight VA241http://www.arianespace.com/press-release/independent-enquiry-commission-announces-conclusions-concerning-the-launcher-trajectory-deviation-during-flight-va241/The key para:QuoteInvestigations by the Independent Enquiry Commission showed that the trajectory anomaly resulted from an incorrect value in specifications for the implementation of the launcher’s two inertial reference systems. 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. The cause of the trajectory deviation, therefore, was due to a bad specification of one of the launcher mission parameters that was not detected during the standard quality checks carried out during the Ariane 5 launches’ preparation chain.
Independent Enquiry Commission announces conclusions concerning the launcher trajectory deviation during Flight VA241http://www.arianespace.com/press-release/independent-enquiry-commission-announces-conclusions-concerning-the-launcher-trajectory-deviation-during-flight-va241/
Investigations by the Independent Enquiry Commission showed that the trajectory anomaly resulted from an incorrect value in specifications for the implementation of the launcher’s two inertial reference systems. 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. The cause of the trajectory deviation, therefore, was due to a bad specification of one of the launcher mission parameters that was not detected during the standard quality checks carried out during the Ariane 5 launches’ preparation chain.
QuoteHow did a 20 degree offset from get go not trigger range safety and FTS?https://twitter.com/toruonu/status/967648161404739584QuoteIt's a question that will be asked. Industry officials say a judgment was made that the rocket was performing well (except for trajectory) and that the danger to local population of debris from flight termination outweighed the dangers of continuing flight.https://twitter.com/pbdes/status/967649386699411456Interesting case study for AFTS?
How did a 20 degree offset from get go not trigger range safety and FTS?
It's a question that will be asked. Industry officials say a judgment was made that the rocket was performing well (except for trajectory) and that the danger to local population of debris from flight termination outweighed the dangers of continuing flight.
Quote from: Remes on 02/24/2018 05:09 pmAriane 5 always used ring laser gyros. No gimbal lock.If it's not the gyros, they why is flight at right angles to the flight path a problem?
Ring Laser Gyros (RLG)Main article: Ring laser gyroA ring laser gyro splits a beam of laser light into two beams in opposite directions through narrow tunnels in a closed circular optical path around the perimeter of a triangular block of temperature-stable Cervit glass with reflecting mirrors placed in each corner. When the gyro is rotating at some angular rate, the distance traveled by each beam becomes different—the shorter path being opposite to the rotation. The phase shift between the two beams can be measured by an interferometer and is proportional to the rate of rotation (Sagnac effect).In practice, at low rotation rates the output frequency can drop to zero as the result of backscattering causing the beams to synchronise and lock together. This is known as a lock-in, or laser-lock. The result is that there is no change in the interference pattern and therefore no measurement change.To unlock the counter-rotating light beams, laser gyros either have independent light paths for the two directions (usually in fiber optic gyros), or the laser gyro is mounted on a piezo-electric dither motor that rapidly vibrates the laser ring back and forth about its input axis through the lock-in region to decouple the light waves.The shaker is the most accurate, because both light beams use exactly the same path. Thus laser gyros retain moving parts, but they do not move as far.https://en.wikipedia.org/wiki/Inertial_navigation_system#Ring_Laser_Gyros_(RLG)
Wouldn't that depend on how it was programmed? An AFTS that merely evaluated how well the rocket was doing compared to planned trajectory would have been perfectly content. Only if "are we nevertheless flying into keep out zones" logic were added would there be some possible termination.I think?
Quote from: LouScheffer on 02/24/2018 09:19 pmQuote from: Remes on 02/24/2018 05:09 pmAriane 5 always used ring laser gyros. No gimbal lock.If it's not the gyros, they why is flight at right angles to the flight path a problem?FWIW, WikiP says that ring laser gyros can undergo laser-lock:
Ils ont donné la chance au lanceur", estime un bon connaisseur du dossier.
QuoteHow did a 20 degree offset from get go not trigger range safety and FTS?
Quote from: FutureSpaceTourist on 02/25/2018 08:15 amQuoteHow did a 20 degree offset from get go not trigger range safety and FTS?Because the vehicle did not go outside the range safety boundary limits