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SpaceX's Autonomous Spaceport Drone Ship Updates and Discussion Thread 3
by
Chris Bergin
on 10 Mar, 2016 01:02
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#1
by
CJ
on 10 Mar, 2016 01:27
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I've been giving some thought to the hole in the deck. I'm not worried it holed the hill bottom too, because the ASDS was most likely ballasted (so there would have been water between the deck and hull bottom).
However... We've seen what LOX and RP1 do when they combine during other hard landings. Now, imagine that happening INSIDE the hull. I hope it didn't.
Incidentally, regarding repairing the hole; assuming there's not significant damage belowdecks, wouldn't slapping a bit over-sized steel plate atop the hole (It'd protrude above deck level, but only by its thickness) and welding it in place be good enough? Especially if there are time constraints?
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#2
by
Lar
on 10 Mar, 2016 01:31
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Incidentally, regarding repairing the hole; assuming there's not significant damage belowdecks, wouldn't slapping a bit over-sized steel plate atop the hole (It'd protrude above deck level, but only by its thickness) and welding it in place be good enough? Especially if there are time constraints?
I expect that depends on what the lease agreement says. Informed speculation holds that these are leased vessels, not purchased, and that they will someday perhaps be returned. The agreement may say that significant damages have to be repaired before returning, or repaired whenever damage happens (in case the return happens early, etc.) so a patch like that might be OK for a while, or might be OK forever, or might not be OK at all because they want a real repair with replacement at the normal seams, not patching....
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#3
by
the_other_Doug
on 10 Mar, 2016 01:33
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Incidentally, regarding repairing the hole; assuming there's not significant damage belowdecks, wouldn't slapping a bit over-sized steel plate atop the hole (It'd protrude above deck level, but only by its thickness) and welding it in place be good enough? Especially if there are time constraints?
I expect that depends on what the lease agreement says. Informed speculation holds that these are leased vessels, not purchased, and that they will someday perhaps be returned. It may say that they have to be repaired before returning, or repaired whenever damage happens (in case the return happens early, eto) so a patch like that might be OK for a while, or might be OK forever, or might not be OK at all.
Also kinda depends on when they'll need OCISLY to sail again, in terms of how quick-and-dirty the fix has to be. As I just inquired in the CSR-8 discussion thread, if they try an RTLS on that flight, we may not have a need for OCISLY for a couple of months or more.
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#4
by
dorkmo
on 10 Mar, 2016 01:35
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I believe a skilled welder could have the deck in like new condition in a day or two. Replacing the damaged equipment will take longer.
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#5
by
OxCartMark
on 10 Mar, 2016 01:35
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#6
by
CameronD
on 10 Mar, 2016 01:35
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I've been giving some thought to the hole in the deck. I'm not worried it holed the hill bottom too, because the ASDS was most likely ballasted (so there would have been water between the deck and hull bottom).
Good point.
However... We've seen what LOX and RP1 do when they combine during other hard landings. Now, imagine that happening INSIDE the hull. I hope it didn't.
Well, there's no evidence from the photo that it did. One would also assume the ballast water to be relatively RP1-free, otherwise they wouldn't be pumping it over the side..
Incidentally, regarding repairing the hole; assuming there's not significant damage belowdecks, wouldn't slapping a bit over-sized steel plate atop the hole (It'd protrude above deck level, but only by its thickness) and welding it in place be good enough? Especially if there are time constraints?
It's really no big deal to cover the hole - cut out the daggy bits and weld a new plate in place. The issue will be if there's any damage to the sub-structure (ribs, deck beams) and needing to repair those first ...to the satisfaction of their local USCG/ABS Inspector.
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#7
by
Kabloona
on 10 Mar, 2016 01:52
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edit: note that it was Kabloona that started the initial thread and he's been active thorough all of this. A fact that Elon recognized when he named the phenomenon that happens when a rocket falls over as "kaboom". 
Thanks for the nod, but pure coincidence I assure you.
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#8
by
Rocket Science
on 10 Mar, 2016 01:53
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Great to hear that Elon wants to go for "another hole in one"...
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#9
by
Kabloona
on 10 Mar, 2016 01:56
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Incidentally, regarding repairing the hole; assuming there's not significant damage belowdecks, wouldn't slapping a bit over-sized steel plate atop the hole (It'd protrude above deck level, but only by its thickness) and welding it in place be good enough? Especially if there are time constraints?
I expect that depends on what the lease agreement says. Informed speculation holds that these are leased vessels, not purchased, and that they will someday perhaps be returned. It may say that they have to be repaired before returning, or repaired whenever damage happens (in case the return happens early, eto) so a patch like that might be OK for a while, or might be OK forever, or might not be OK at all.
Also kinda depends on when they'll need OCISLY to sail again, in terms of how quick-and-dirty the fix has to be. As I just inquired in the CSR-8 discussion thread, if they try an RTLS on that flight, we may not have a need for OCISLY for a couple of months or more.
Someone just pointed out in the CRS-8 thread that the mission patch has been posted on Reddit and does not show a barge, FWIW.
And RTLS landing would give them more time to repair the barge, plus give them a higher probability of successful recovery, so I'm inclined to believe the barge will be out of action for a while.
(I had thought Elon's tweet implied next flight would be another barge landing attempt, but now I think I read too much into it.)
Elon Musk @elonmusk
Rocket landed hard on the droneship. Didn't expect this one to work (v hot reentry), but next flight has a good chance.
"Next flight has a good chance" because it will be RTLS?
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#10
by
Wolfram66
on 10 Mar, 2016 02:58
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Falcon 9 uses an open hydraulic system that has a separate tank of RP-1 (which is used as the hydraulic fluid) pressurized by Nitrogen near the interstage, which, after use, drains down back into the main RP-1 tank for "reuse" by the engines. There are a variety of reasons that SpaceX made decisions to use this design:
A closed hydraulic system separate of the main RP-1 tank would require a pump to repressurize the RP-1 for reuse. This adds weight and complexity to something which you really don't want to make much heavier or more complex.
A closed hydraulic system that uses the RP-1 from the main tank is also infeasible as it would require a pump to push RP-1 up from the tank near the engines right to the top of the vehicle. There is no easy way of doing this.
Switching to an electromechanical system would require a very large amount of power to operate, which would require an impractical amount of batteries.
All three of the above solutions require pumps to be active or some energy storage mechanism - not very attractive or really suitable for Falcon 9 as the engines are only burning over a subset of the return trajectory.
The grid fins are deployed at approximately T+5 minutes. This is before the reentry burn takes place, which does not last for very long. For the majority of the time the grid fins are deployed, Falcon 9 is in free flight. SpaceX's solution is rather clever, actually:
It does not require power from the engines to operate.
It doesn't involve a complex plumbing solution which adds weight to lift the RP-1 up from the bottom tank
It doesn't add much mass beyond the pressure vessel, since the RP-1 is "free" as it can be "reused" by the engines.
Overall, it weighs less than a similar amount of pressurized Nitrogen cold gas to steer.
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#11
by
OxCartMark
on 10 Mar, 2016 03:15
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Falcon 9 uses an open hydraulic system that has a separate tank of RP-1 (which is used as the hydraulic fluid) pressurized by Nitrogen near the interstage, which, after use, drains down back into the main RP-1 tank for "reuse" by the engines. There are a variety of reasons that SpaceX made decisions to use this design:
I don't think its been established that the hydraulic fluid being used is fuel. I don't think its been established that the expended fluid goes into the main fuel tank. These have been speculated as likely and seem so but I don't think its been proven. Or am I wrong?
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#12
by
CJ
on 10 Mar, 2016 03:20
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I believe a skilled welder could have the deck in like new condition in a day or two. Replacing the damaged equipment will take longer.
Good point. I've done some welding (I'm not good at it though) so what I'd look at first is what's damaged below the deck plate: that, IMHO, will be the hard part, because we'd be talking structural members.
It's also IMHO a question of when it needs to be done by.
As mentioned upthread, there's no ASDS on the CRS-8 mission patch, which strongly hints at a RTLS. If the F9 1.2 (or should I call it F9 FT?) has the capacity to do RTLS on a Dragon launch, my strong guess is that doing so would be the preferred option. If so, OCISLY may have plenty of time for repairs, refurbishment, R&R, etc.
Incidentally, regarding repairing the hole; assuming there's not significant damage belowdecks, wouldn't slapping a bit over-sized steel plate atop the hole (It'd protrude above deck level, but only by its thickness) and welding it in place be good enough? Especially if there are time constraints?
I expect that depends on what the lease agreement says. Informed speculation holds that these are leased vessels, not purchased, and that they will someday perhaps be returned. The agreement may say that significant damages have to be repaired before returning, or repaired whenever damage happens (in case the return happens early, etc.) so a patch like that might be OK for a while, or might be OK forever, or might not be OK at all because they want a real repair with replacement at the normal seams, not patching....
I've never dealt with a maritime lease, but I've dealt with all sorts of commercial building leases. *IF* there's a similarity, a temporary repair would be okay for a while under most, especially if it's needed to avoid any downtime. The caveats would be that the temp repair does not risk further damage, and meets codes. On the other hand, most commercial building owners would not be okay with the lessee firing enormous rockets at it.
However... We've seen what LOX and RP1 do when they combine during other hard landings. Now, imagine that happening INSIDE the hull. I hope it didn't.
Well, there's no evidence from the photo that it did. One would also assume the ballast water to be relatively RP1-free, otherwise they wouldn't be pumping it over the side..
Good point; pumping water over the side is indeed a pretty clear indication of no contamination. You also raised an excellent point regarding stratifying inspectors when it comes to fixing the hole. I darkly suspect that'll take much longer than the actual repairs.
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#13
by
Comga
on 10 Mar, 2016 04:19
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Falcon 9 uses an open hydraulic system that has a separate tank of RP-1 (which is used as the hydraulic fluid) pressurized by Nitrogen near the interstage, which, after use, drains down back into the main RP-1 tank for "reuse" by the engines. There are a variety of reasons that SpaceX made decisions to use this design:
I don't think its been established that the hydraulic fluid being used is fuel. I don't think its been established that the expended fluid goes into the main fuel tank. These have been speculated as likely and seem so but I don't think its been proven. Or am I wrong?
Wolfram66 is stating all this as facts.
Either its complete and detailed speculation without any statement to that effect ...
or Wolfram66 is in a position to know and to discuss it in a public thread.
I certainly hope it's the latter as this is precisely the kind of details I want to learn about and understand.
PS If SpaceX is using fuel that gets dumped into the fuel tank, why wouldn't they pressurized with Helium?
There is a large supply of He and it's the gas already being used to pressurize the fuel.
Is it because they need an even higher pressure, because the hydraulic actuators would be powered by the differential pressure, and the fuel tank drain is itself pressurized?
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#14
by
CameronD
on 10 Mar, 2016 04:52
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Incidentally, regarding repairing the hole; assuming there's not significant damage belowdecks, wouldn't slapping a bit over-sized steel plate atop the hole (It'd protrude above deck level, but only by its thickness) and welding it in place be good enough? Especially if there are time constraints?
I expect that depends on what the lease agreement says. Informed speculation holds that these are leased vessels, not purchased, and that they will someday perhaps be returned. The agreement may say that significant damages have to be repaired before returning, or repaired whenever damage happens (in case the return happens early, etc.) so a patch like that might be OK for a while, or might be OK forever, or might not be OK at all because they want a real repair with replacement at the normal seams, not patching....
I've never dealt with a maritime lease, but I've dealt with all sorts of commercial building leases. *IF* there's a similarity, a temporary repair would be okay for a while under most, especially if it's needed to avoid any downtime. The caveats would be that the temp repair does not risk further damage, and meets codes. On the other hand, most commercial building owners would not be okay with the lessee firing enormous rockets at it.
Lease or no lease, the way the maritime regulations stand, that hole needs to be fixed to the satisfaction of the USCG, ABS, SpaceX, the owners, workers, insurers and any other Joe who happens by... so there really isn't any option other than to fix it properly.
At the end of the day, unless the ASDS is "in all respects fit for sea", it doesn't go anywhere.
However... We've seen what LOX and RP1 do when they combine during other hard landings. Now, imagine that happening INSIDE the hull. I hope it didn't.
Well, there's no evidence from the photo that it did. One would also assume the ballast water to be relatively RP1-free, otherwise they wouldn't be pumping it over the side..
Good point; pumping water over the side is indeed a pretty clear indication of no contamination. You also raised an excellent point regarding stratifying inspectors when it comes to fixing the hole. I darkly suspect that'll take much longer than the actual repairs.
"Stratifying inspectors".. I like that. Stringing 'em up and hosing 'em down doesn't work either.
Anyways, it really depends on the extent of the damage. If whatever-it-was managed to miss anything vital (given the hole is located in the corner of one of the tanks as can be seen by following the deck-plate joins they sure came mighty close!) it could be just a quick phone call, drive down, peek in the hole, "she'll be right" and weld it all back up again.
...but if they took out a rib or deck beam or two then, yes, that could take a while.
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#15
by
BlazingAngel665
on 10 Mar, 2016 05:30
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Falcon 9 uses an open hydraulic system that has a separate tank of RP-1 (which is used as the hydraulic fluid) pressurized by Nitrogen near the interstage, which, after use, drains down back into the main RP-1 tank for "reuse" by the engines. There are a variety of reasons that SpaceX made decisions to use this design:
I don't think its been established that the hydraulic fluid being used is fuel. I don't think its been established that the expended fluid goes into the main fuel tank. These have been speculated as likely and seem so but I don't think its been proven. Or am I wrong?
Wolfram66 is stating all this as facts.
Either its complete and detailed speculation without any statement to that effect ...
or Wolfram66 is in a position to know and to discuss it in a public thread.
I certainly hope it's the latter as this is precisely the kind of details I want to learn about and understand.
PS If SpaceX is using fuel that gets dumped into the fuel tank, why wouldn't they pressurized with Helium?
There is a large supply of He and it's the gas already being used to pressurize the fuel.
Is it because they need an even higher pressure, because the hydraulic actuators would be powered by the differential pressure, and the fuel tank drain is itself pressurized?
Most of what Wolfram66 has said meshes well with what is known for certain. Elon's tweets after the first ASDS hard landing tell us that the hydraulic system is definitely open loop. Using Nitrogen as a pressurant makes good sense based upon the location of all the components. RP-1 is used as a hydraulic fluid for TVC so it makes good sense to use it again for gridfin actuation. Finally we know that the reserve of fluid for the grid fins is separate from the normal RP-1 supply and non replenish-able, so having a separate reservoir makes sense as well. I'd treat most of that as fairly certain.
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#16
by
Robotbeat
on 10 Mar, 2016 05:40
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I doubt you'd use RP-1 if you're using a separate reservoir.
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#17
by
vanoord
on 10 Mar, 2016 07:22
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I doubt you'd use RP-1 if you're using a separate reservoir.
Propylene glycol and water would be sufficient - with the advantage it can be discharged overboard after use as it's non-toxic.
I don't like the idea of using RP-1 and trying to return the waste to the main tank: I doubt the pressure in the grid fin hydraulic system is higher than the tank - which would prevent it getting there after use.
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#18
by
Kabloona
on 10 Mar, 2016 07:41
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Falcon 9 uses an open hydraulic system that has a separate tank of RP-1 (which is used as the hydraulic fluid) pressurized by Nitrogen near the interstage, which, after use, drains down back into the main RP-1 tank for "reuse" by the engines.
I don't believe this is correct, and in any case what does it have to do with the ASDS? Wrong thread.
Grid fin hydraulic thread is over here:
http://forum.nasaspaceflight.com/index.php?topic=36536.0Back to ASDS topics, please...
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#19
by
symbios
on 10 Mar, 2016 10:41
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...
Incidentally, regarding repairing the hole; assuming there's not significant damage belowdecks, wouldn't slapping a bit over-sized steel plate atop the hole (It'd protrude above deck level, but only by its thickness) and welding it in place be good enough? Especially if there are time constraints?
It is never recommended to fixing a hole by slapping a patch over it. You will get moisture in between the plates and this will cause corrosion. Always cut out the bad part and weld in a new plate. It is not like it is a lot more work; it would only be sloppy workmanship not to.
