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Loiter time on orbit of Dragon



 
 
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  #1  
Old May 30th 12, 08:32 AM posted to sci.space.station
Brian Gaff
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Default Loiter time on orbit of Dragon

I see they are bringing Dragon down quite quickly compared to other cargo
delivery craft, and I wondered if this was just due to it being an early
test flight, or whether there is an issue over prolonged time on orbit.

Brian

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  #2  
Old May 30th 12, 09:10 AM posted to sci.space.station
Jochem Huhmann
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Default Loiter time on orbit of Dragon

"Brian Gaff" writes:

I see they are bringing Dragon down quite quickly compared to other cargo
delivery craft, and I wondered if this was just due to it being an early
test flight, or whether there is an issue over prolonged time on orbit.


Sane thing to do with a craft that never was in orbit for longer than a
few hours before. Dragon has lots of hypergolic fuels on board, lots of
valves and plumbing... You certainly don't want it do develop a leak
somewhere or a connector corroding while docked to the ISS.

Getting it down as soon as it has done its job at the ISS and going over it
with a fine comb afterwards is just sensible I'd say.


Jochem

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longer anything to add, but when there is no longer anything to take away."
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  #4  
Old May 30th 12, 09:35 PM posted to sci.space.station
Chris Jones
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Default Loiter time on orbit of Dragon

JF Mezei writes:

[...]

How did the russians arrive at 6 months for Soyuz ? Testing on earth ?
Empirical testing on Mir ? Or just mathematical calculations ?


It's actually somewhat longer (around 210-220 days). They have tested
it (unmanned) for that long. I've heard several reasons for the
lifetime: seals in the propulsion system degrading, and hydrogen
peroxide (used for attitude control for the descent module during
reentry) decomposing over time.
  #6  
Old May 31st 12, 02:06 PM posted to sci.space.station
Jeff Findley[_2_]
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Posts: 1,388
Default Loiter time on orbit of Dragon

In article m,
says...

Say Dragon had been designed for 6 months in space.

Wouldn't they want it to stay long enough to gauge whether they can see
any degradation ?


Not necessarily. This is only Dragon's second flight!

Traditionally, aerospace programs expand the flight envelope in
increments. The reasoning is that it's better to get your vehicle back
in one piece, so you can inspect it and correct any defects, than it
would be to push your luck a bit too far, too early, and get the vehicle
back in tiny bits and pieces.

Perhaps longevity testing is scheduled for he next flight.

How did the russians arrive at 6 months for Soyuz ? Testing on earth ?
Empirical testing on Mir ? Or just mathematical calculations ?


Soyuz is reportedly limited by the decomposition of the H2O2 used in the
descent module's reaction control system.

I'm not sure about Progress, but I'm guessing it's limited more by
operational issues, like freeing up a docking port for the next Progress
that wants to dock. In this respect, all visiting US commercial cargo
and crew vehicles will be limited in the same way.

Since crews are rotated every six months for Soyuz, it wouldn't surprise
me that six months becomes the requirement for a US crewed vehicle as
well. Having the same rotation schedule as Soyuz would seem to make
planning ISS crew rotations easier.

Jeff
--
" Ares 1 is a prime example of the fact that NASA just can't get it
up anymore... and when they can, it doesn't stay up long. "
- tinker
  #7  
Old May 31st 12, 04:00 PM posted to sci.space.station
Jeff Findley[_2_]
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Posts: 1,388
Default Loiter time on orbit of Dragon

In article ,
says...

In article m,
says...

Say Dragon had been designed for 6 months in space.

Wouldn't they want it to stay long enough to gauge whether they can see
any degradation ?


Not necessarily. This is only Dragon's second flight!

Traditionally, aerospace programs expand the flight envelope in
increments. The reasoning is that it's better to get your vehicle back
in one piece, so you can inspect it and correct any defects, than it
would be to push your luck a bit too far, too early, and get the vehicle
back in tiny bits and pieces.

Perhaps longevity testing is scheduled for he next flight.

How did the russians arrive at 6 months for Soyuz ? Testing on earth ?
Empirical testing on Mir ? Or just mathematical calculations ?


Soyuz is reportedly limited by the decomposition of the H2O2 used in the
descent module's reaction control system.

I'm not sure about Progress, but I'm guessing it's limited more by
operational issues, like freeing up a docking port for the next Progress
that wants to dock. In this respect, all visiting US commercial cargo
and crew vehicles will be limited in the same way.

Since crews are rotated every six months for Soyuz, it wouldn't surprise
me that six months becomes the requirement for a US crewed vehicle as
well. Having the same rotation schedule as Soyuz would seem to make
planning ISS crew rotations easier.


In an online article (see my other post), it said that DragonLab could
stay in orbit up to two years, so it would seem that a Dragon could stay
docked to ISS for an equal amount of time.

Jeff
--
" Ares 1 is a prime example of the fact that NASA just can't get it
up anymore... and when they can, it doesn't stay up long. "
- tinker
  #8  
Old May 31st 12, 07:37 PM posted to sci.space.station
snidely
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Posts: 1,303
Default Loiter time on orbit of Dragon

Brian Gaff presented the following explanation :
I see they are bringing Dragon down quite quickly compared to other cargo
delivery craft, and I wondered if this was just due to it being an early test
flight, or whether there is an issue over prolonged time on orbit.


And it's down (as AE noted in the STS group).

From Spaceflight Now:

quote
THURSDAY, MAY 31, 2012
1549 GMT (11:49 a.m. EDT)
SpaceX founder and chief designer Elon Musk just tweeted: "Splashdown
successful!! Sending fast boat to Dragon lat/long provided by P3
tracking planes."

The recovery team includes a 185-foot barge, an 80-foot crew boat, and
two 25-foot fast boats for dispatch to the capsule when it splashes
down.
/quote

and
quote
THURSDAY, MAY 31, 2012
1820 GMT (2:20 p.m. EDT)
Speaking with reporters from SpaceX headquarters in California, Elon
Musk says recovery crews are in the process of attaching cables to the
Dragon spacecraft to hoist it on the deck of a ship for the trip back
to port.

Dragon's re-entry and splashdown were very accurate, he said.

"It appears as though we were really hitting the bullseye in accuracy,
perhaps less than a mile," Musk said.

"In baseball terminology, this would be a grand slam," Musk said. "This
was bigger success than we had a reasonable right to expect."
/quote
(P3/submarine jokes elided)
http://spaceflightnow.com/falcon9/003/status.html

/dps

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Who, me? And what lacuna?


 




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