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#720
by
mn
on 22 Feb, 2017 14:14
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SpaceX Dragon Rendezvous and Docking Waved Off for Today
Posted on February 22, 2017 at 4:38 am by mcsumner.
The SpaceX Dragon cargo spacecraft waved off its planned rendezvous with the International Space Station at 3:25 a.m. EST. Onboard computers triggered the abort after recognizing an incorrect value in data about the location of the space station. Per the re-rendezvous plan built into every mission, the spacecraft automatically reset for another rendezvous and docking attempt in 24 hours.
The spacecraft is in excellent shape with no issues, and the crew aboard the space station is safe. The next rendezvous attempt is targeted for Thursday morning. NASA TV coverage will begin at 4 a.m. with grapple expected around 6 a.m. Installation coverage will begin at 8 a.m. Watch live on NASA TV and online at: http://www.nasa.gov/live.
https://blogs.nasa.gov/spacestation/2017/02/22/spacex-dragon-rendezvous-and-docking-waved-off-for-today/
Any reason why it must be a 24 hour delay?
I understand that the automatic reset could be for 24 hours, but I would assume they can send up new commands to proceed earlier?
(don't they have to send up new commands anyway to fix the issue? or is there a reason to allow the autonomous code run it's course - maybe they are deliberately waiting just to verify the autonomous code in real life?)
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#721
by
Roy_H
on 22 Feb, 2017 15:20
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Just guessing, but I imagine it would be more fuel efficient to circle the ISS slowly than quickly. They could of course choose not to circle the ISS, but another reason for the 24 hours is to allow lots of time to solve unknown problem.
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#722
by
CraigLieb
on 22 Feb, 2017 17:30
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Just guessing, but I imagine it would be more fuel efficient to circle the ISS slowly than quickly. They could of course choose not to circle the ISS, but another reason for the 24 hours is to allow lots of time to solve unknown problem.
rescheduling activities on the ISS for the crew may also play a role...
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#723
by
ChrisGebhardt
on 22 Feb, 2017 18:07
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Just guessing, but I imagine it would be more fuel efficient to circle the ISS slowly than quickly. They could of course choose not to circle the ISS, but another reason for the 24 hours is to allow lots of time to solve unknown problem.
rescheduling activities on the ISS for the crew may also play a role...
It's the crew schedule, yes.
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#724
by
butters
on 22 Feb, 2017 18:51
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Was the incorrect data coming from the ISS or pre-loaded into Dragon computers?
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#725
by
nacnud
on 22 Feb, 2017 19:52
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Just guessing, but I imagine it would be more fuel efficient to circle the ISS slowly than quickly. They could of course choose not to circle the ISS, but another reason for the 24 hours is to allow lots of time to solve unknown problem.
If the dragon is sitting just below the station and moving at the same speed it will move around the station once per orbit.
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#726
by
ChrisC
on 22 Feb, 2017 20:36
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I've got a question about the second stage reentry. In the launch updates thread, these two reentry map images were posted (click the quote links to see the images):
This was from Raul's hazard map. If you zoom out far enough to see Australia, you'll see the re-entry hazard zone for the upper stage. I have seen no information on the accuracy of the actual reentry. This was just the planned area.
Something like this orbit
The first is the NOTAM map showing a region extending down to 61 deg South.
The second is the ISS orbital track showing paths down to the nominal 51.6 deg South. The thing is, that reentry is NOT something like that orbit, for reasonable values of "something"
Why was the reentry zone planned for so much further south than the orbital track? 10 degrees of inclination is nothing to sneeze at. Was SpaceX doing a delta-V / plane-change test with their second stage, after Dragon sep?
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#727
by
whitelancer64
on 22 Feb, 2017 20:57
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#728
by
ChrisC
on 22 Feb, 2017 21:33
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Look at the 2nd stage re-entry track in the spaceflight101 article. http://spaceflight101.com/dragon-spx10/falcon-9-deorbit-burn-seen-over-iran-kuwait/
I assume you're talking about
this image. That's a ground track, not a reentry zone. Those video views were due to fuel dumps and the very brief deorbit burn. Reentry would still be very far downrange -- recall the Shuttle deorbit burns which would take place near Australia, yet land in US? Thank you, but my question stands
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#729
by
intrepidpursuit
on 23 Feb, 2017 03:39
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Look at the 2nd stage re-entry track in the spaceflight101 article. http://spaceflight101.com/dragon-spx10/falcon-9-deorbit-burn-seen-over-iran-kuwait/
I assume you're talking about this image. That's a ground track, not a reentry zone. Those video views were due to fuel dumps and the very brief deorbit burn. Reentry would still be very far downrange -- recall the Shuttle deorbit burns which would take place near Australia, yet land in US? Thank you, but my question stands
So, your question revolves around the reentry zone going further south than the inclination of the station. It looks like the zone is also much wider than it needs to be. I think somebody just had to calculate the worst case scenario for the reentry zone, such as if it lost TVC during the burn but didn't shut off the engine, how far off track could it go before it ran out of fuel. I think you are just reading too much into it.
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#730
by
whitelancer64
on 23 Feb, 2017 14:05
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Look at the 2nd stage re-entry track in the spaceflight101 article. http://spaceflight101.com/dragon-spx10/falcon-9-deorbit-burn-seen-over-iran-kuwait/
I assume you're talking about this image. That's a ground track, not a reentry zone. Those video views were due to fuel dumps and the very brief deorbit burn. Reentry would still be very far downrange -- recall the Shuttle deorbit burns which would take place near Australia, yet land in US? Thank you, but my question stands
Do the ground track image and the "something like this orbit" image match up?
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#731
by
Comga
on 23 Feb, 2017 15:11
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Just guessing, but I imagine it would be more fuel efficient to circle the ISS slowly than quickly. They could of course choose not to circle the ISS, but another reason for the 24 hours is to allow lots of time to solve unknown problem.
I believe that the Dragon circled the ISS once per orbit.
There is no "fast" vs "slow" circling, only the relative distance.
They have to keep the same orbital period, which means the same semi-major axis. The orbit is just given some ellipticity and the distance can be made to stay relatively constant without further maneuvering.
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#732
by
mn
on 23 Feb, 2017 19:15
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#733
by
Orbiter
on 23 Feb, 2017 19:59
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Anyone know if the first stage is still at LZ-1?
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#734
by
Herb Schaltegger
on 23 Feb, 2017 21:16
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Interestingly if you look here: https://www.n2yo.com/?s=42053|25544 dragon and iss are still far apart. (not sure how many miles, no idea how to translate lat/lng to miles)
Edit: 273.5 km according to http://www.movable-type.co.uk/scripts/latlong.html.
Edit 2: this is not taking into account altitude.
Sites like n2yo just take the published TLEs and propagate "current" positions based on the data. They are only accurate to the extent they use current and accurate TLE data, which is typically generated by Space Command. Sometimes n2yo and similar sites are on the spot and use the absolute latest data but often - expecially for maneuvering spacecraft - they are more likely to be wrong than right. This has to do with how often the site retrieves the latest public TLEs as well as how often Space Command generates them, which in turn generates how often tracking assets are available, how interested Space Command and its government customers are in the spacecraft, etc.
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#735
by
ChrisC
on 24 Feb, 2017 04:01
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The first is the NOTAM map showing a region extending down to 61 deg South. The second is the ISS orbital track showing paths down to the nominal 51.6 deg South. The thing is, that reentry is NOT something like that orbit, for reasonable values of "something" Why was the reentry zone planned for so much further south than the orbital track? 10 degrees of inclination is nothing to sneeze at. Was SpaceX doing a delta-V / plane-change test with their second stage, after Dragon sep?
Do the ground track image and the "something like this orbit" image match up?
Ha, NO, hence the question
So, your question revolves around the reentry zone going further south than the inclination of the station. It looks like the zone is also much wider than it needs to be. I think somebody just had to calculate the worst case scenario for the reentry zone, such as if it lost TVC during the burn but didn't shut off the engine, how far off track could it go before it ran out of fuel. I think you are just reading too much into it.
If that was the case, I would expect an extremely wide impact zone that straddled the nominal orbit track, not a zone biased in one direction.
Nobody else is jumping in on this 10-deg plane change with delta-V calcs and whatnot, so I guess I am reading into it.
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#736
by
Lar
on 24 Feb, 2017 04:15
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I would if I understood it.
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#737
by
M.E.T.
on 24 Feb, 2017 07:43
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In a worst case scenario, do we know how many berthing attempts the Dragon's fuel capacity can provide for, before having insufficient propellant left for a successful return to Earth?
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#738
by
Kaputnik
on 24 Feb, 2017 08:46
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In a worst case scenario, do we know how many berthing attempts the Dragon's fuel capacity can provide for, before having insufficient propellant left for a successful return to Earth?
I can't answer that, but would like to add to it- is it technically or procedurally possible to adjust the ISS's own position to make up for a shortfall in performance of a VV?
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#739
by
LouScheffer
on 24 Feb, 2017 13:53
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I've got a question about the second stage reentry. In the launch updates thread, these two reentry map images were posted (click the quote links to see the images):
This was from Raul's hazard map. If you zoom out far enough to see Australia, you'll see the re-entry hazard zone for the upper stage. I have seen no information on the accuracy of the actual reentry. This was just the planned area.
Something like this orbit
The first is the NOTAM map showing a region extending down to 61 deg South.
The second is the ISS orbital track showing paths down to the nominal 51.6 deg South. The thing is, that reentry is NOT something like that orbit, for reasonable values of "something"
Why was the reentry zone planned for so much further south than the orbital track? 10 degrees of inclination is nothing to sneeze at. Was SpaceX doing a delta-V / plane-change test with their second stage, after Dragon sep?
I agree that without a maneuver, the impact zone should not extend south of the southernmost ground track. A back of the envelope calculation makes a maneuver look possible. To change orbital plane by 10 degrees will take something like 1000 m/s of delta V. But the second stage is quite light after separating from Dragon, something like 5000 kg. Given the vacuum thrust of 911kn, that's something like 182 m/s (18G) acceleration. So only a 5-6 second burn would be required, and it's certainly possible they had that type of reserves.
