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#440
by
kevin-rf
on 05 Oct, 2013 16:03
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Most likely they did not plan to, and no one ad-libs with rockets. The stage did not start for a reason...
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#441
by
Hooperball
on 05 Oct, 2013 16:12
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Elon indicated in his post launch interview that the restart issue was not mechanical and that it had to do with the start sequence in zero G and vacuum.
He also indicated this issue could be easily resolved via tweaks in the automation.
This leads us to believe auto start and engine run parameters such as max / min pressure time limits for auto shut down may be changed.
S
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#442
by
Lar
on 05 Oct, 2013 16:15
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I'm glad we could resolve this before it made xkcd "What If."
Not me, I think that would be a highly amusing one... you should go suggest it!
Randall is definitely a space, NASA and probably SpaceX fan so it would be fun to see his take.
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#443
by
Ben the Space Brit
on 05 Oct, 2013 19:12
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So, has anyone heard any updates on the CASSIOPE mission itself? Is the satellite in a viable orbit and is it working properly?
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#444
by
jcm
on 06 Oct, 2013 06:09
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So, has anyone heard any updates on the CASSIOPE mission itself? Is the satellite in a viable orbit and is it working properly?
Yes, Richard Langley is PI on the GPS experiment - he runs the CANSPACE list of GPS users and has been talking
about the fact that he's in the middle of calibrating his stuff, so they are talking to the satellite and it is basically working.
I gather the satellite is close to object B.
Space-track have labelled object G as the rocket stage. I am dubious as they have also now got RCS values for the
objects. Although these are notoriously hard to interpret, object B has an RCS of 22 sq meters and object G only 0.6 sq m.
N is 0.7, all the others are smaller. I continue to suspect that B is actually a cloud of objects close together.
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#445
by
llanitedave
on 06 Oct, 2013 14:44
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I would think such a cloud would have spread out and dissipated by now.
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#446
by
Ben the Space Brit
on 06 Oct, 2013 16:05
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That depends on the initial energy. If it was low, they would all still be on broadly-similar orbital tracks and metallic debris tends to screw up radar returns anyway (see 'Chaff' for more details). So a cloud of debris would look a lot like a single object to a ground-based radar.
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#447
by
Avron
on 06 Oct, 2013 17:25
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Elon indicated in his post launch interview that the restart issue was not mechanical and that it had to do with the start sequence in zero G and vacuum.
He also indicated this issue could be easily resolved via tweaks in the automation.
This leads us to believe auto start and engine run parameters such as max / min pressure time limits for auto shut down may be changed.
S
If its a simple parameter change, why not upload the new parameters and try again.. or maybe its burned in to so Rom.
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#448
by
Avron
on 06 Oct, 2013 17:31
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I've been following this discussion with some bemusement. I'm waiting to see if SpaceX is going to post the video of the descent. If it shows that the stage was spinning before the final single engine burn was started, then I'm not sure what the argument has been about.
Talking of videos, I asked Elon via Twitter ( don't think he will notice, who knows), but has anyone seen said video..
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#449
by
Hooperball
on 06 Oct, 2013 17:57
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If its a simple parameter change, why not upload the new parameters and try again.. or maybe its burned in to so Rom.
Thats what a couple other people were asking as well..... the fluid venting after SECO1 in the video did look pretty sketchy....
S
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#450
by
douglas100
on 06 Oct, 2013 20:10
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And the usual reply was that launch vehicles are autonomous. They are not set up to be reprogrammed on the fly. There is very little time to do that anyway, since the upper stage has a short life.
SpaceX will look at the data, determine the cause of the failure and make whatever changes are needed in the next F9 to prevent it happening again. This is the sensible way to proceed. Of course they will have to convince their customer that the problem has been fixed.
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#451
by
Okie_Steve
on 06 Oct, 2013 21:53
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It seems like the second stage non-restart was due to some difference between the terrestrial environment where Elon says they tested restart many times (as expected) and the space environment where the first stage engines did restart and the second stage engine did not. Vacuum and micro-gravity have been posited. I guess another difference could be temporal depending on the time between shutdown and restart of the various engines. Given the supposed commonality between the booster and vacuum versions I tend to discount (but not entirely rule out) engine differences as a likely factor.
Anyone have time stamps for the various shutdown and restarts/attempts? I doubt much can be done in the way of direct testing of the micro-gravity idea (lighting a Merlin inside the vomit comet is contraindicated) but is there a vacuum chamber big enough to at least get a burp out of a Merlin here dirt side to compare with the on orbit data? For that matter, what would the ambient pressure have been during the first restart of the first stage vs the aborted second stage restart?
I'm sure they are looking at all the data in great detail, just scratching my head and pondering until there is some official word or action.
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#452
by
douglas100
on 06 Oct, 2013 22:09
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The previous M-vac was successfully restarted in orbit. Of course this is a substantially new engine. But most other contemporary launch vehicles have restartable upper stages (Ariane 5 ECA is an exception).
As you say, we have to wait to see what they decide to release about the problem and its solution.
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#453
by
Avron
on 06 Oct, 2013 22:56
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It seems like the second stage non-restart was due to some difference between the terrestrial environment where Elon says they tested restart many times (as expected) and the space environment where the first stage engines did restart and the second stage engine did not. Vacuum and micro-gravity have been posited. I guess another difference could be temporal depending on the time between shutdown and restart of the various engines. Given the supposed commonality between the booster and vacuum versions I tend to discount (but not entirely rule out) engine differences as a likely factor.
Anyone have time stamps for the various shutdown and restarts/attempts? I doubt much can be done in the way of direct testing of the micro-gravity idea (lighting a Merlin inside the vomit comet is contraindicated) but is there a vacuum chamber big enough to at least get a burp out of a Merlin here dirt side to compare with the on orbit data? For that matter, what would the ambient pressure have been during the first restart of the first stage vs the aborted second stage restart?
I'm sure they are looking at all the data in great detail, just scratching my head and pondering until there is some official word or action.
I guess one could test in a vacuum via GH2.. by the time GH2 Flies , SPACEX may already be recovering stages in Florida..
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#454
by
sdsds
on 06 Oct, 2013 23:20
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Any idea why they couldn't try re-starting the second stage again, and instead opted to vent the tanks?
Suppose SpaceX had programmed the second stage to wait for instructions, rather than vent, if the first restart attempt failed due to exceeding some limit. The life of the stage is measured in minutes. How many minutes would mission controllers need to decide on a new course of action, given that a wrong choice might lead the stage to rapidly disassemble itself? Would they wait until the next orbital pass over their telemetry assets, in which case the engine start conditions would have changed yet again?
As others have indicated, this is an essential difference between an ascent stage that reaches orbit, and a spacecraft. The Falcon 9 upper stage is the former, not the latter!
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#455
by
Okie_Steve
on 06 Oct, 2013 23:56
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I guess one could test in a vacuum via GH2.. by the time GH2 Flies , SPACEX may already be recovering stages in Florida..
Umm, I think that would essentially reproduce the suborbital first stage environment where restart worked not the orbital second stage environment where it did not.
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#456
by
kevin-rf
on 07 Oct, 2013 00:36
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The previous M-vac was successfully restarted in orbit. Of course this is a substantially new engine. But most other contemporary launch vehicles have restartable upper stages (Ariane 5 ECA is an exception).
As you say, we have to wait to see what they decide to release about the problem and its solution.
Aaah, but on the first Falcon 9 flight the attempted second burn with the original M-Vac engine also failed. It led to a spiral and much Australian UFO sightings.
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#457
by
Robotbeat
on 07 Oct, 2013 01:09
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Any idea why they couldn't try re-starting the second stage again, and instead opted to vent the tanks?
Suppose SpaceX had programmed the second stage to wait for instructions, rather than vent, if the first restart attempt failed due to exceeding some limit. The life of the stage is measured in minutes. How many minutes would mission controllers need to decide on a new course of action, given that a wrong choice might lead the stage to rapidly disassemble itself? Would they wait until the next orbital pass over their telemetry assets, in which case the engine start conditions would have changed yet again?
As others have indicated, this is an essential difference between an ascent stage that reaches orbit, and a spacecraft. The Falcon 9 upper stage is the former, not the latter!
Even still, I wonder if eventually the line will be blurred... The ability to command an upper stage must have at least SOME merit. So many launch vehicle problems are software-related, you have to wonder if the ability to fix the stage on-orbit may be a worthwhile risk-reduction capability.
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#458
by
Lars_J
on 07 Oct, 2013 01:10
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The previous M-vac was successfully restarted in orbit. Of course this is a substantially new engine. But most other contemporary launch vehicles have restartable upper stages (Ariane 5 ECA is an exception).
As you say, we have to wait to see what they decide to release about the problem and its solution.
Aaah, but on the first Falcon 9 flight the attempted second burn with the original M-Vac engine also failed. It led to a spiral and much Australian UFO sightings.
Indeed, this seems like a very similar situation, although the root cause might be different. But an upper stage restart was achieved on the second F9 flight.
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#459
by
Okie_Steve
on 07 Oct, 2013 01:43
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Indeed, this seems like a very similar situation, although the root cause might be different. But an upper stage restart was achieved on the second F9 flight.
I hope it's clear from the telemetry and has an easy fix. Some times 20-20 hindsight makes things obvious - like happened with the stage "bump" on the F1 flight where thrust transients from the then-new Merlin-1C regen were not seen during atmospheric testing but were critical to allow for in vacuum operation. Adding a 5 second delay took care of it. For want of a nail ...
