Author Topic: Dragon Capsule docking procedure to ISS  (Read 762 times)

Offline smartcooky

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Dragon Capsule docking procedure to ISS
« on: March 03, 2019, 06:34:50 PM »
OK, so SpaceX and NASA have taken the penultimate step before America returns to manned space flight. The uncrewed Dragon Capsule was launched a couple of days ago, and has docked with ISS. If it returns safely the next step (NET May 2019) is the In Flight Abort Test where they will test the capsule's escape system during an actual launch, and if all goes well, SpaceX will launch two astronauts (Bob Behnken and Dan Hurley) to the space station NET July 2019. I have been following this mission live on SpaceX and NASA TV, and I have a question for our aerospace experts here.

I was surprised by the many hours of extensive testing they had to do before opening the hatch. I understand the need to make sure that the capsule has been correctly captured and air-sealed, but they just seemed to go through a great long procedure not unlike a cockpit checklist only much, much longer. When when they finally opened it, they put on masks and breathing equipment before going in, then they took air samples... what a rigmarole!

Do they go through all this hours long procedure every time a capsule docks, or is it something related to this being the first time up for this capsule?
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Offline Zakalwe

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Re: Dragon Capsule docking procedure to ISS
« Reply #1 on: March 03, 2019, 08:49:07 PM »
I believe that the primary concern was that Freon may have leaked into the capsule from the life support system. The automatic detection systems are seemingly poor at detecting Freon levels.
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Offline ka9q

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Re: Dragon Capsule docking procedure to ISS
« Reply #2 on: March 03, 2019, 11:26:35 PM »
I was also surprised by the lengthy delay, though I assume there was a good reason for it. You have to admit that, aside from launches, NASA isn't exactly known for gripping television. A friend who once saw me watching it opined that it was "watching grass grow". I couldn't really disagree...

I found this regarding the abort test: http://www.parabolicarc.com/2018/11/28/how-spacex-conduct-inflight-abort-test-crew-dragon/

It does surprise me that they're going to expend (and not even try to recover) an entire Falcon 9 on this test. Only the second stage engine will be omitted. The Apollo in-flight abort tests were conducted with the Little Joe solid rocket, which was certainly much cheaper than a complete Saturn I or V; why couldn't the same be done here?

That document is a little contradictory as to exactly how the abort will be triggered. It first says
Quote
The Falcon 9 would be configured to shut down and terminate thrust, targeting the abort test shutdown condition (simulating a loss of thrust scenario).
but then says
Quote
Dragon would then autonomously detect and issue an abort command, which would initiate the nominal startup sequence of Dragon’s SuperDraco engine system. Concurrently, Falcon 9 would receive a command from Dragon to terminate thrust on the nine first stage Merlin 1D (M1D) engines.
Which is it for this flight? Maybe they meant to say that in a general abort scenario Dragon would issue a shutdown command, but not in this particular case.

Since this was extracted from an environmental impact statement, it occurs to me that an abort around max-Q has considerably greater environmental impact than a successful launch, especially when the first stage is recovered. There's also no use or release of hypergolic propellants.
 

Offline smartcooky

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Re: Dragon Capsule docking procedure to ISS
« Reply #3 on: March 04, 2019, 06:14:08 AM »
I was also surprised by the lengthy delay, though I assume there was a good reason for it. You have to admit that, aside from launches, NASA isn't exactly known for gripping television. A friend who once saw me watching it opined that it was "watching grass grow". I couldn't really disagree...

I was sitting there watching and waiting, and couldn't help being reminded of Tim Grimes' remark from the movie, "The Martian" when they were trying to establish comms between Watney and NASA using the two Mars Pathfinders...

"32-minute round-trip communications time. All he can do is ask yes or no questions and all we can do is point the camera. This won’t exactly be an Algonquin Round Table of snappy repartee."

I found this regarding the abort test: http://www.parabolicarc.com/2018/11/28/how-spacex-conduct-inflight-abort-test-crew-dragon/

It does surprise me that they're going to expend (and not even try to recover) an entire Falcon 9 on this test. Only the second stage engine will be omitted. The Apollo in-flight abort tests were conducted with the Little Joe solid rocket, which was certainly much cheaper than a complete Saturn I or V; why couldn't the same be done here?

That document is a little contradictory as to exactly how the abort will be triggered. It first says
Quote
The Falcon 9 would be configured to shut down and terminate thrust, targeting the abort test shutdown condition (simulating a loss of thrust scenario).
but then says
Quote
Dragon would then autonomously detect and issue an abort command, which would initiate the nominal startup sequence of Dragon’s SuperDraco engine system. Concurrently, Falcon 9 would receive a command from Dragon to terminate thrust on the nine first stage Merlin 1D (M1D) engines.
Which is it for this flight? Maybe they meant to say that in a general abort scenario Dragon would issue a shutdown command, but not in this particular case.

Since this was extracted from an environmental impact statement, it occurs to me that an abort around max-Q has considerably greater environmental impact than a successful launch, especially when the first stage is recovered. There's also no use or release of hypergolic propellants.
 

Perhaps the system is designed to shut all all nine first stage Merlin engines down in the case of a partial loss of thrust. They can lose any two engines and the computer will automatically reconfigure the flight profile using engine gimballing and a longer burn on the remaining engines, and still make it to orbit. However it can't lose three. In that case, if I'm in that capsule, I don't want any if the first stage engines still running while I'm pulling away from it.
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Offline bknight

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Re: Dragon Capsule docking procedure to ISS
« Reply #4 on: March 04, 2019, 06:24:10 AM »
I also wondered why they were going to expend a rocket for the abort test.
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Offline Peter B

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Re: Dragon Capsule docking procedure to ISS
« Reply #5 on: March 04, 2019, 07:59:46 AM »
I also wondered why they were going to expend a rocket for the abort test.

The parabolicarc article appears to give a hint: "The abort test would involve observation, photography, and debris management associated with the breakup of the Falcon 9 first and second stages." It sounds to me like they'd like real experience of what happens to a Falcon 9 when it disintegrates in this sort of situation.


Offline jfb

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Re: Dragon Capsule docking procedure to ISS
« Reply #6 on: March 04, 2019, 01:51:14 PM »
I also wondered why they were going to expend a rocket for the abort test.

It's not clear that the rocket will be aerodynamically stable at Max-Q when the Dragon and trunk separate.  You're suddenly changing center of mass, center of pressure, aerodynamic characteristics, etc., when aero loads are the greatest.  I don't think anyone at SpaceX expects it to survive the event intact. 

And this will be a pre-flown booster, so it's not like they're throwing away brand-new equipment. 

And, sometimes, testing to destruction is exactly what's called for. 

Offline Dalhousie

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Re: Dragon Capsule docking procedure to ISS
« Reply #7 on: March 30, 2019, 12:08:58 AM »
OK, so SpaceX and NASA have taken the penultimate step before America returns to manned space flight.

NASA never left manned space flight. What you may mean is a return of US manned launches (although that happened with Virgin Galactic some time ago).  So a return to US Manned orbital launches.
« Last Edit: March 30, 2019, 12:10:31 AM by Dalhousie »