Author Topic: Ariane 5 VA241-SES-14 (with NASA GOLD payload) Al Yah-3 Jan. 25, 2018-DISCUSSION  (Read 60004 times)

Offline envy887

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What happened is that someone entered an incorrect parameter value (initial azimuth) into the guidance system parameter repository.

Causing the guidance system to provide incorrect guidance i.e. malfunction.

No. The guidance system flew the trajectory exactly as it had been programmed to do. Unfortunately, this deviated from what the trajectory was designed to be. Classic parameter input error.

The guidance system in itself did not fail. It flew exactly what it was told to fly, to the best of its ability. What it had been told to do was incorrect.
That is malfunction, but not of the guidance system. It is malfunction of the quality control system.

From the point of view of the RSO, this is irrelevant. WHY the vehicle is flying off course does not matter, the mere fact that it IS in fact flying off course is proof that it is not "healthy". Calling it an anomaly or a programming error instead of a malfunction doesn't change this.

A vehicle that is not following the nominal trajectory (regardless of the reason) is potentially dangerous because it is impossible to tell in real time how the deviation is going to progress. That is why the vehicle isn't (or shouldn't be) allowed to leave the IIP bounds, even if altitude and velocity are nominal.
« Last Edit: 03/20/2018 08:21 PM by envy887 »

Offline redox



Any french speakers here that understands what the DDO said at 1:02? tendue [tense] is not good.

"Les paramètres à bord sont conformes à l'attendu"
== The parameters on board are in line with what is expected.
For the spectators, he announced only what was good, not what was bad.

Offline woods170

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No. You don't understand. The CEO of Arianespace does not have a hotline with the CSG range safety office. Simply because there is no need to.
The range safety office is not there to prevent the Arianespace CEO from looking like an idiot.

You're suggesting some animosity between Arianespace and the CSG operations people?

No, that is not what I'm suggesting. What I am referring to is how the Arianespace CEO fumbled, live on the webcast, when it had become clear something had gone wrong without knowing what had gone wrong. The CSG range safety officer is not there to prevent the Arianespace CEO from fumbling (looking like an idiot) on a live webcast.

Offline woods170

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All others, including the DDO, are fed secondary-source information. That is because there is no need for a primary source. If a vehicle strays off-course there is nothing that anyone in the Jupiter control room can do about it.

So if they can't act on the information, it should not be presented? I understand this is how it is currently handled. Do you think it will change after VA241?
Not going to change after VA241. Even if the information is shown they still cannot act to correct the flight-path in real-time.
The solution is making sure that the initiating error (incorrect input of azimuth in the flight paramater repository of the guidance system) cannot be made again.

Offline woods170

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Fact.  They had telemetry data, we know this and the vehicle's state vector is part of it.

...

Wouldn't telemetry be just as off course as the guidance? wouldn't both be taking info from the same incorrectly initialized IMU?

Without radar data, it seems to me all the telemetry in the world would not tell them they were off course?

Telemetry is basically the rocket telling to the ground what the rocket is doing. The ground compares this to what the rocket is supposed to do. And thus telemetry is usually very helpful in telling what went wrong (mostly after the mishap has taken place).

Offline mn

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Fact.  They had telemetry data, we know this and the vehicle's state vector is part of it.

...

Wouldn't telemetry be just as off course as the guidance? wouldn't both be taking info from the same incorrectly initialized IMU?

Without radar data, it seems to me all the telemetry in the world would not tell them they were off course?

Telemetry is basically the rocket telling to the ground what the rocket is doing. The ground compares this to what the rocket is supposed to do. And thus telemetry is usually very helpful in telling what went wrong (mostly after the mishap has taken place).

I understand the 'usually' but I'm trying to understand this specific case. if the IMU was incorrect initialized, am I correct in understanding that telemetry data would have been saying they are going right on course despite being 20 deg off course. Or am I missing something?

Edit: corrected 30 deg to 20 deg, thanks Lars-J.
« Last Edit: 03/21/2018 05:18 PM by mn »

Offline redox

I understand the 'usually' but I'm trying to understand this specific case. if the IMU was incorrect initialized, am I correct in understanding that telemetry data would have been saying they are going right on course despite being 30 deg off course. Or am I missing something?

It is likely the 1st part of the real data (the yellow line going to the South), was obtained from radar and as soon as the rocket was out of sight of the radar, the telemetry was displayed, coming back to where the rocket thought she was == the nominal line.

Offline cscott

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Just a quick point: the guidance system likely reports its residual errors as well.  If the residual errors are small, the guidance system is "in control" and guidance is (in that sense) nominal... even if the rocket isn't going where you want it to.  So it's meaningful to have a policy to delay a range safety destruct if residuals are remaining small.

Offline envy887

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Just a quick point: the guidance system likely reports its residual errors as well.  If the residual errors are small, the guidance system is "in control" and guidance is (in that sense) nominal... even if the rocket isn't going where you want it to.  So it's meaningful to have a policy to delay a range safety destruct if residuals are remaining small.

True, but a guidance trying to match the wrong trajectory can be in perfect control and still go somewhere you don't want it to go, potentially up to and including destroying the vehicle. Which is the why the range has radar tracking, to independently verify that the trajectory is in bounds.

Offline Lars-J

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if the IMU was incorrect initialized, am I correct in understanding that telemetry data would have been saying they are going right on course despite being 30 deg off course. Or am I missing something?

You are absolutely correct, this is what happened.  (although I think it was closer to 20 degrees off rather than 30)

Which is why the rocket thinking that everything is going fine should be irrelevant from a range safety point of view. And as the saying goes, for every rocket failure ever, the rocket looked 100% fine until it wasn't.

Offline woods170

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Fact.  They had telemetry data, we know this and the vehicle's state vector is part of it.

...

Wouldn't telemetry be just as off course as the guidance? wouldn't both be taking info from the same incorrectly initialized IMU?

Without radar data, it seems to me all the telemetry in the world would not tell them they were off course?

Telemetry is basically the rocket telling to the ground what the rocket is doing. The ground compares this to what the rocket is supposed to do. And thus telemetry is usually very helpful in telling what went wrong (mostly after the mishap has taken place).

I understand the 'usually' but I'm trying to understand this specific case. if the IMU was incorrect initialized, am I correct in understanding that telemetry data would have been saying they are going right on course despite being 30 deg off course. Or am I missing something?

It would neither say it was on the right course, nor would it say it was 30 degrees off course. It would say it was flying a 70 degree azimuth.

Telemetry reports facts, not conclusions.

Offline Steven Pietrobon

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It would neither say it was on the right course, nor would it say it was 30 degrees off course. It would say it was flying a 70 degree azimuth.

The computer was programmed to fly a 90 degree azimuth, which is the value it reported in its telemetry. According to the computer, everything was fine. However, the IMU was rotated by 20 degrees north from normal, so needed to be programmed with a 70 degree azimuth in order to fly a true 90 degree azimuth. Programming with 90 degrees meant the vehicle flew at 110 degree azimuth.

A possible fix is that the data pack for the launch vehicle includes the IMU azimuth (0 for normal, 20 degrees for special case), vehicle azimuth on the launch pad, launch site location, etc. This IMU azimuth gets entered into the ground software (along with all the other parameters). The operator enters the azimuth they want, say 90 degrees. The ground software then subtracts the IMU azimuth and programs the IMU with 70 degrees. In the telemetry, the ground software would have to add the IMU azimuth, otherwise the vehicle would show it is flying at 70 degrees!

Another solution is that during installation, the IMU is programmed with its azimuth (0 for normal, 20 for special). The IMU then subtracts this value before use, and adds this value for the telemetry. So, one solution has the ground software handling the offset, the other has the IMU handling the offset.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Lars-J

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Telemetry reports facts, not conclusions.

Just be aware that those telemetry 'facts' aren't necessarily true, as this case illustrates. They need to be verified against another source.
« Last Edit: 03/22/2018 03:21 AM by Lars-J »

Online deruch

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https://twitter.com/pbdes/status/1001818027153862656
Quote
30 May 2018
Peter B. de Selding
‏ @pbdes

UAE's @yahsatofficial: IOT done,  Al Yah 3 sat ready for service at 20degW; Ka-band in Africa/Brazil. @Eutelsat a customer in Africa. ~43% loss of rev capacity w/ 5-month, fuel-using trip to GEO slot after off-target @Arianespace Ariane 5 in Jan; $108M insurance claim likely.   <emphasis added>

 ???  what he means:" w/ 5-month, fuel-using trip to GEO slot after off-target @Arianespace Ariane 5 in Jan; " ?

the chemical fuel for the apogee-motor from Al-Yah 3 was about mid Februar over.
after that they used the XR-5 electric engines. about on 04/25/2018 reached Al-Yah 3 a orbit slightly over GEO and drifted without force one week 1°/day  to his slot 20.1W and stopped on 05/01 or 05/02

Though I'm not sure, my read was that the ~43% loss of revenue capacity was just for the 1st year of operation as opposed to lifetime revenue.  That would make more sense, as the $108M he notes as the likely insurance claim seems too small for a claim on 43% of lifetime revenue capacity.  Or, that claim is a combination of it having taken much longer to reach operational status than originally planned and the operational cost of having to use a bunch of extra fuel--beyond what had originally been budgeted for the orbit raising prior to launch--to reach their GEO location.  I think that second bit is what he's talking about with "fuel-using trip to GEO".
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline cscott

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https://twitter.com/pbdes/status/1001818027153862656
Quote
30 May 2018
Peter B. de Selding
‏ @pbdes

UAE's @yahsatofficial: IOT done,  Al Yah 3 sat ready for service at 20degW; Ka-band in Africa/Brazil. @Eutelsat a customer in Africa. ~43% loss of rev capacity w/ 5-month, fuel-using trip to GEO slot after off-target @Arianespace Ariane 5 in Jan; $108M insurance claim likely.   <emphasis added>



 ???  what he means:" w/ 5-month, fuel-using trip to GEO slot after off-target @Arianespace Ariane 5 in Jan; " ?

the chemical fuel for the apogee-motor from Al-Yah 3 was about mid Februar over.
after that they used the XR-5 electric engines. about on 04/25/2018 reached Al-Yah 3 a orbit slightly over GEO and drifted without force one week 1°/day  to his slot 20.1W and stopped on 05/01 or 05/02
I interpreted it as meaning the trip took 5 months (losing revenue for those for those months) and used an (indeterminate) amount of fuel, not that the trip took 5 months worth of fuel.

Incidentally five months is 42% of the year.
« Last Edit: 06/02/2018 02:19 AM by cscott »

Online starbase

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Arianespace launchers will get an autonomous range safety system, named Kassav. It will be first tested on Ariane 5 in late 2019 (Kassav 1) and incorporated into Ariane 6 and Vega C from the beginning, reaching maturity (Kassav 2) by 2021.

Quote
LYON, France—French space agency CNES has tapped Zodiac Data Systems for the development of an autonomous range safety system at Arianespace’s Kourou, French Guiana launch site, thus making the destruction of an off-course launcher an automated process.
...

Source: https://twitter.com/AviationWeek/status/1022421592884830209
http://aviationweek.com/space/arianespace-launchers-get-autonomous-range-safety-system

edit/gongora: 1.  Do not post an entire copyrighted article  2.  Do not make the same post in Update and Discussion threads.  3.  This post doesn't really belong here but I'm not sure where it should go, maybe the not-too-old Ariane 5 Upgrades thread?
« Last Edit: 07/26/2018 03:16 PM by gongora »

Offline GWR64

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Al Yah 3 Launch Documentary:



Yahsat employees tell how they experienced the drama.

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