Forgot to change the azimuth: the results of the investigation of the accident with "Ariane 5"
The emergency commission investigating the incident with the Ariane 5 launch vehicle on January 25 published the results of its work last week. The reason turned out to be ridiculously simple and offensive, as well as very instructive - changing the standard flight mission due to the special requirements of the mission, forgot to correct the azimuth, and a perfectly working rocket flew away from the required route.
Start PH "Ariane 5", photo Arianespace
The Ariane 5 rocket with two telecommunication satellites Al Yah 3 and SES-14 was launched on January 25 at 22:30 UTC. According to the broadcast, it seemed that the flight was proceeding normally, but at the tenth minute the telemetry data from the rocket ceased to be displayed in it. The host of the broadcast did not comment on this fact, so stopping the broadcast at 38 minutes and reporting the anomaly an hour later was an unpleasant surprise. About an hour more went to search for satellites. Finally it turned out that the satellites are in orbit, but with a larger inclination of 20 °.
Approximate flight track, user scheme Cheburashka Forum magazine "News of Cosmonautics"
Already on the first day, according to publicly available information - a broadcast of the launch and video of a rocket’s flight, taken off the ground, it became clear that for some reason Ariane flew about 20 degrees south of (to the right) the correct course. Telemetry really disappeared, and this happened because for the stations receiving data from the rocket, it disappeared over the horizon. Only the emergency commission could answer the question why this happened.
In the meantime, the satellites began to move from a geotransfer to a geostationary orbit. Equipped with chemical and electric engines, Al Yah 3 moves faster than SES 14 with only electric engines.
The average height of the orbit is growing, the source
And the inclination falls, the source
Unfortunately, the fuel to enter the geostationary orbit will have to spend more than the initial optimistic calculations. It would take only 165 m / s to correct only the improper inclination, but Ariane 5 brought satellites into an orbit where the apocenter and pericenter are not at the equator (and this is required by a normal geo-transition orbit). Due to the natural precession of the orbit, they would eventually be there, but would have to wait until about September. Judging by the fact that the satellites began to move, they found some solution better than to wait eight months, but it would be necessary to spend up to 1100 m / s to correct this problem.
The published findings of the commission suggest that the rocket was fully operational, but did the wrong flight task. Due to the “special requirements” of the mission, the azimuth for the inertial navigation system should have been set to 70 ° instead of the usual 90 °. But they did not, and the pre-launch checks did not reveal an error. Alas, the press release describes the reason too briefly (literally a couple of lines after praising the rocket's health and before assuring that this will not happen again), so you will have to look for additional information and clarify what was meant.
According to the French magazine Aero Spatium, the uniqueness of the mission was that one of the customers demanded to separate its satellite perpendicular to the flight direction. To do this, it was necessary to deploy the upper stage, and it seems that this created some problems for the control system, which, obviously, was physically turned 20 ° so that the separation would take place at an angle of 70 ° rather than 90. Because of this, it was necessary to introduce changes in the flight program. The rocket flew along the same trajectory as before, but the rotated control system was supposed to direct the rocket at an azimuth of 70 °. And they forgot to make this change to the program. As a result, the control system turned the Ariane 5 to the usual azimuth of 90 °, which in this case superimposed on the rotation of the control system itself, and the rocket flew on a course of 90 + 20 = 110 °.
The question of why physically turned the control system remains unanswered. If on the rocket there was a gyrostabilized platform with mechanical gyroscopes, the version about the danger of folding the gyros' frames would be obvious. But on Ariane 5 there are laser gyroscopes that do not have frames and are not afraid of this problem.
Training class of crash operators, source
It is also very sad that the report of the emergency commission does not say a word about the behavior of emergency flight cessation (RSO) operators. On the one hand, the rocket was indeed operational. On the other hand, it flew at an obviously wrong course, which was beyond the limits of the permitted and ran only a couple of kilometers from the densely populated city. And we cannot say whether the RSO received insufficient information, were able to quickly assess the situation and conclude that the rocket should not be undermined, or simply could not respond in time. Personally, the first option seems unlikely to me - a faulty control system can inform you about the “right” direction of flight, therefore external control systems are logical. And from the last two options, it seems to me, the latter is more likely. It is unlikely that people under stress can quickly assess the effects of a course error of 20 °, and here it is logical to use simple algorithms - “if we fly the wrong way, then stop flying”.
Just two months after the accident of the Russian Frigate, Arianespace managed to arrange an incident for a very similar reason - a change is made to the design and the flight plan, causing an error that is not trapped by existing checks, and a completely intact technique creates problems. And the incident clearly demonstrates that in astronautics one cannot relax - 15 trouble-free years and 83 start-ups (of all versions of Ariane 5) do not provide reliability by themselves. Even worse - the ugly coverage of the incident shows that everyone has relaxed, even the public relations services. But, paradoxically, in such an incident you can find the positive side - in 2019, Ariane 5 should launch the James Webb telescope worth $ 9 billion. And after the accident, people's vigilance increases for a while.
Start PH "Ariane 5", photo Arianespace
Chronicle of events and consequences
The Ariane 5 rocket with two telecommunication satellites Al Yah 3 and SES-14 was launched on January 25 at 22:30 UTC. According to the broadcast, it seemed that the flight was proceeding normally, but at the tenth minute the telemetry data from the rocket ceased to be displayed in it. The host of the broadcast did not comment on this fact, so stopping the broadcast at 38 minutes and reporting the anomaly an hour later was an unpleasant surprise. About an hour more went to search for satellites. Finally it turned out that the satellites are in orbit, but with a larger inclination of 20 °.
Approximate flight track, user scheme Cheburashka Forum magazine "News of Cosmonautics"
Already on the first day, according to publicly available information - a broadcast of the launch and video of a rocket’s flight, taken off the ground, it became clear that for some reason Ariane flew about 20 degrees south of (to the right) the correct course. Telemetry really disappeared, and this happened because for the stations receiving data from the rocket, it disappeared over the horizon. Only the emergency commission could answer the question why this happened.
In the meantime, the satellites began to move from a geotransfer to a geostationary orbit. Equipped with chemical and electric engines, Al Yah 3 moves faster than SES 14 with only electric engines.
The average height of the orbit is growing, the source
And the inclination falls, the source
Unfortunately, the fuel to enter the geostationary orbit will have to spend more than the initial optimistic calculations. It would take only 165 m / s to correct only the improper inclination, but Ariane 5 brought satellites into an orbit where the apocenter and pericenter are not at the equator (and this is required by a normal geo-transition orbit). Due to the natural precession of the orbit, they would eventually be there, but would have to wait until about September. Judging by the fact that the satellites began to move, they found some solution better than to wait eight months, but it would be necessary to spend up to 1100 m / s to correct this problem.
Results and questions
The published findings of the commission suggest that the rocket was fully operational, but did the wrong flight task. Due to the “special requirements” of the mission, the azimuth for the inertial navigation system should have been set to 70 ° instead of the usual 90 °. But they did not, and the pre-launch checks did not reveal an error. Alas, the press release describes the reason too briefly (literally a couple of lines after praising the rocket's health and before assuring that this will not happen again), so you will have to look for additional information and clarify what was meant.
According to the French magazine Aero Spatium, the uniqueness of the mission was that one of the customers demanded to separate its satellite perpendicular to the flight direction. To do this, it was necessary to deploy the upper stage, and it seems that this created some problems for the control system, which, obviously, was physically turned 20 ° so that the separation would take place at an angle of 70 ° rather than 90. Because of this, it was necessary to introduce changes in the flight program. The rocket flew along the same trajectory as before, but the rotated control system was supposed to direct the rocket at an azimuth of 70 °. And they forgot to make this change to the program. As a result, the control system turned the Ariane 5 to the usual azimuth of 90 °, which in this case superimposed on the rotation of the control system itself, and the rocket flew on a course of 90 + 20 = 110 °.
The question of why physically turned the control system remains unanswered. If on the rocket there was a gyrostabilized platform with mechanical gyroscopes, the version about the danger of folding the gyros' frames would be obvious. But on Ariane 5 there are laser gyroscopes that do not have frames and are not afraid of this problem.
Training class of crash operators, source
It is also very sad that the report of the emergency commission does not say a word about the behavior of emergency flight cessation (RSO) operators. On the one hand, the rocket was indeed operational. On the other hand, it flew at an obviously wrong course, which was beyond the limits of the permitted and ran only a couple of kilometers from the densely populated city. And we cannot say whether the RSO received insufficient information, were able to quickly assess the situation and conclude that the rocket should not be undermined, or simply could not respond in time. Personally, the first option seems unlikely to me - a faulty control system can inform you about the “right” direction of flight, therefore external control systems are logical. And from the last two options, it seems to me, the latter is more likely. It is unlikely that people under stress can quickly assess the effects of a course error of 20 °, and here it is logical to use simple algorithms - “if we fly the wrong way, then stop flying”.
Conclusion
Just two months after the accident of the Russian Frigate, Arianespace managed to arrange an incident for a very similar reason - a change is made to the design and the flight plan, causing an error that is not trapped by existing checks, and a completely intact technique creates problems. And the incident clearly demonstrates that in astronautics one cannot relax - 15 trouble-free years and 83 start-ups (of all versions of Ariane 5) do not provide reliability by themselves. Even worse - the ugly coverage of the incident shows that everyone has relaxed, even the public relations services. But, paradoxically, in such an incident you can find the positive side - in 2019, Ariane 5 should launch the James Webb telescope worth $ 9 billion. And after the accident, people's vigilance increases for a while.
Source: https://habr.com/ru/post/410417/