Author Topic: Ariane 5 VA241-SES-14 (with NASA GOLD payload) Al Yah-3 Jan. 25, 2018-DISCUSSION  (Read 55822 times)

Offline Galactic Penguin SST

43174/2018-012A: 232 x 43163 km x 20.64 deg.
43175/2018-012B: 232 x 43198 km x 20.64 deg.
43176/2018-012C: 169 x 42790 km x 21.01 deg.
43177/2018-012D: 235 x 43153 km x 20.64 deg.
The planned orbit was 250 x 45234 km x 3.00 deg.

Unless I made a mistake there's at least 3km/s delta V difference between the actual and planned orbits at perigee... I find it hard to believe that the upper stage has that much extra performance....

Wait, 3km/s makes no sense to me, isn't 20 or so degree what you get by launch to GTO from the Cape? From the Cape you get GTO-1800 and from Kourou you get GTO-1500, so shouldn't the difference in delta-V be 300m/s?

The 300 m/s figure is the velocity change you do if you decrease the orbit inclination at apogee at around 36000 km high. This time the Ariane 5 did that just 200 km above us, which is far more costly.
Chinese spaceflight is a cosmic riddle wrapped in a galactic mystery inside an orbital enigma... - (not) Winston Churchill

Offline satwatcher

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There are suggestions that the EPC was targeting the wrong azimuth. See this tweet: https://twitter.com/arcoholle/status/956828845398810625
and also the screencap shown earlier in this thread: http://forum.nasaspaceflight.com/index.php?topic=42215.msg1777220#msg1777220

I've attached a zoom of the screencap, which shows the white line going South from Kourou.

Offline satwatcher

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And here is a comparison of the 43174 orbit at the time of launch with that of the V-238 EPC, propagated to the V-241 launch time. If it was just the upper stage responsible for the different inclination, the intersections of the two planes should be further East, out over the see. Downrange at the EPS cut-off was 1500 km.

Offline yokem55

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With these TLE's, I'm a bit flabbergasted that Ariane is looking at keeping at their manifest as scheduled.

Either they already have a really, really good idea of what happened, or I'm afraid they are taking the wrong lesson from SpaceX's response to Zuma.

Online acsawdey

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With these TLE's, I'm a bit flabbergasted that Ariane is looking at keeping at their manifest as scheduled.

Either they already have a really, really good idea of what happened, or I'm afraid they are taking the wrong lesson from SpaceX's response to Zuma.

Software error? Somebody typed the wrong thing in the inputs to the guidance? Then this sounds like the Fregat issue with the launch of Meteor back in November.

Offline starsilk

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With these TLE's, I'm a bit flabbergasted that Ariane is looking at keeping at their manifest as scheduled.

Either they already have a really, really good idea of what happened, or I'm afraid they are taking the wrong lesson from SpaceX's response to Zuma.

Software error? Somebody typed the wrong thing in the inputs to the guidance? Then this sounds like the Fregat issue with the launch of Meteor back in November.

it would certainly explain the intention to keep launching. but a horrible procedural error which should have been caught at multiple stages of review, surely.

Offline sewebster

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The 300 m/s figure is the velocity change you do if you decrease the orbit inclination at apogee at around 36000 km high. This time the Ariane 5 did that just 200 km above us, which is far more costly.

But as CorvusCorax points out, they weren't changing an orbit, they were creating one, so it would cost very little to go to an inclined orbit?

An inclination *change* while in orbit  requires that much deltav. If you accelerate in the wrong direction during launch, from equator, theres almost no difference. only thing you are loosining is a tiny bit of extra boost from earth rotation

And as su27k points out, it should only be a few hundred m/s to change the inclination by 20 deg, right? Think of GTO1800 vs GTO1500?

Offline sewebster

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With these TLE's, I'm a bit flabbergasted that Ariane is looking at keeping at their manifest as scheduled.

Either they already have a really, really good idea of what happened, or I'm afraid they are taking the wrong lesson from SpaceX's response to Zuma.

I think this just means they haven't changed anything YET. E.g. they will keep building rockets etc. for now.

Online acsawdey

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The 300 m/s figure is the velocity change you do if you decrease the orbit inclination at apogee at around 36000 km high. This time the Ariane 5 did that just 200 km above us, which is far more costly.

But as CorvusCorax points out, they weren't changing an orbit, they were creating one, so it would cost very little to go to an inclined orbit?

An inclination *change* while in orbit  requires that much deltav. If you accelerate in the wrong direction during launch, from equator, theres almost no difference. only thing you are loosining is a tiny bit of extra boost from earth rotation

And as su27k points out, it should only be a few hundred m/s to change the inclination by 20 deg, right? Think of GTO1800 vs GTO1500?

Even less than that since this was a supersync -- the 300 m/s is if you change at apogee of 36000 km but the starting orbit has apogee of 43000 km so it will be less.

The only reason they could announce they are going to go on with their launch schedule is if the error was immediately and completely understood.

Offline satwatcher

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And as su27k points out, it should only be a few hundred m/s to change the inclination by 20 deg, right? Think of GTO1800 vs GTO1500?
That's for an inclination change at apogee. This one was at perigee!

Online acsawdey

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And as su27k points out, it should only be a few hundred m/s to change the inclination by 20 deg, right? Think of GTO1800 vs GTO1500?
That's for an inclination change at apogee. This one was at perigee!

Well, the cost of an inclination change at launch is 0 m/s  :P


Offline Galactic Penguin SST

The problem with the theory of the rocket being flown in the wrong azimuth all along is: why didn't the rocket self destruct? :o

I have checked the real time trajectory maps for the last 2 A5 launches (VA239 - ECA version to standard GTO and VA240 - ES version to Galileo MEO) and neither had shown deviations like the one a few post above. In addition, there was a small "kink" in the altitude data for this flight at around 7 minutes in the flight, when the real time cursor on the trajectory map shifted back north - perhaps because of the shift of ground station (?).
Chinese spaceflight is a cosmic riddle wrapped in a galactic mystery inside an orbital enigma... - (not) Winston Churchill

Offline sewebster

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The problem with the theory of the rocket being flown in the wrong azimuth all along is: why didn't the rocket self destruct? :o

Good thing they don't have AFTS? (do they?)

Offline starsilk

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The problem with the theory of the rocket being flown in the wrong azimuth all along is: why didn't the rocket self destruct? :o

I have checked the real time trajectory maps for the last 2 A5 launches (VA239 - ECA version to standard GTO and VA240 - ES version to Galileo MEO) and neither had shown deviations like the one a few post above. In addition, there was a small "kink" in the altitude data for this flight at around 7 minutes in the flight, when the real time cursor on the trajectory map shifted back north - perhaps because of the shift of ground station (?).

perhaps the same reason the announcer kept reading out details that clearly weren't true. when they lost telemetry, various displays just started showing what was *supposed* to be happening, not what really was occuring.

Offline LouScheffer

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Orbit data from Space Track are in:

43174/2018-012A: 232 x 43163 km x 20.64 deg.
43175/2018-012B: 232 x 43198 km x 20.64 deg.
43176/2018-012C: 169 x 42790 km x 21.01 deg.
43177/2018-012D: 235 x 43153 km x 20.64 deg.

Yes your eyes are not deceiving - the trajectory was so wrong that the satellites ultimately got pushed to 21 degrees inclination orbits! 😑

The planned orbit was 250 x 45234 km x 3.00 deg.

Although Ariane does not use parking orbits, we can do this calculation to guess the effect.

To get from a 250x250x7o parking orbit to a 250x45000x3o orbit takes about 2650 m/s, by my estimate.  This is what was planned.

If you increase, rather than decrease the inclination (an aiming error) it takes about 3350 m/s to reach the observed orbit of 250x4200x20.5o.  Ariane does not use parking orbits, so they should be more efficient at this, so it's plausible that the stage had enough excess performance to do this.  However it would need to be pretty efficient to do so.  So a nice, stable burn, just in the wrong direction.  And a lot in the wrong direction - instead of the burn being +9o to the North of the equator to reduce the inclination, it needs to be 55o to the South, to increase the inclination.  This would explain the lack of telemetry - it's way far from where the antenna would be pointing.

I get about 1630 m/s to get from the final orbit to GEO.  The intended one was about 1465 m/s.  So about 165 m/s more for the satellite.


Offline SLC

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The problem with the theory of the rocket being flown in the wrong azimuth all along is: why didn't the rocket self destruct? :o

Good thing they don't have AFTS? (do they?)

But if it was a programming error so that the wrong course was fed in to start with, and then the rocket obediently flies along that wrong course, the FTS will think everything is fine.  It'll only self-destruct if the real course deviates from the programmed one.

Offline Eosterwine

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The problem with the theory of the rocket being flown in the wrong azimuth all along is: why didn't the rocket self destruct? :o


Is the destruct command issued from mission control or an automated sequence on the rocket?  Maybe it didnt self destruct because as far as it was concerned it was flying exactly where the software told it to,.... the problem being someone told it to go in slightly the wrong direction  :o :o

Offline RonM

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I get about 1630 m/s to get from the final orbit to GEO.  The intended one was about 1465 m/s.  So about 165 m/s more for the satellite.

What's the impact on the propellant reserves needing the extra 165 m/s to reach the proper orbits?

Offline sewebster

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I get about 1630 m/s to get from the final orbit to GEO.  The intended one was about 1465 m/s.  So about 165 m/s more for the satellite.

What's the impact on the propellant reserves needing the extra 165 m/s to reach the proper orbits?

If it's about 50 m/s per year for stationkeeping in geostationary orbit (source: https://en.wikipedia.org/wiki/Delta-v_budget) then that's about 3 years. SES might have a ton extra with their electric propulsion though...

Offline starsilk

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I get about 1630 m/s to get from the final orbit to GEO.  The intended one was about 1465 m/s.  So about 165 m/s more for the satellite.

What's the impact on the propellant reserves needing the extra 165 m/s to reach the proper orbits?

wikipedia (fount of all knowledge) says 45m/s for north/south control per year and 2m/s for east/west per year.

https://en.wikipedia.org/wiki/Orbital_station-keeping#Station-keeping_in_geostationary_orbit

so 3.5 years of lifespan lost.. that sucks.

EDIT: sucks a lot less than losing the satellites, so there's that.
« Last Edit: 01/26/2018 04:33 PM by starsilk »

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