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  #1  
Old August 5th 12, 09:51 AM posted to sci.space.station
Brian Gaff
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Default Express supply..

Now they can resupply in 6 hours, one assumes only if the orbit and pad are
in the correct relationships, it seems that its not that difficult after
all. I'm sure the old reason for not doing this was due to excessive fuel
use to achieve it in relation to the more leisurely way. Was or is this
true, or was it just an excuse?

Brian

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  #2  
Old August 6th 12, 12:17 AM posted to sci.space.station
Brian Thorn[_2_]
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Default Express supply..

On Sun, 5 Aug 2012 09:51:17 +0100, "Brian Gaff"
wrote:

Now they can resupply in 6 hours, one assumes only if the orbit and pad are
in the correct relationships, it seems that its not that difficult after
all.


I think higher latitudes have more opportunities, because the Earth's
rotation is drawing a smaller circle up that far north, and the
distance between the pad and the orbit increases more slowly. You
still need sophisticated avionics, and only the recent upgrade to the
digital flight control system of Soyuz/Progress made it feasible.

Brian
  #3  
Old August 11th 12, 01:24 AM posted to sci.space.station
Korben Dallas[_2_]
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Default Express supply..

On 8/5/2012 1:51 AM, Brian Gaff wrote:
Now they can resupply in 6 hours, one assumes only if the orbit and pad are
in the correct relationships, it seems that its not that difficult after
all. I'm sure the old reason for not doing this was due to excessive fuel
use to achieve it in relation to the more leisurely way. Was or is this
true, or was it just an excuse?


the old obstacle for doing this was lower iss orbit. the iss orbital
altitude was intentionally reduced to make it reachable by space
shuttle. now, with shuttle out of the picture, the iss was transferred
to a notably higher orbit, making it much easier to shoot progress ships
straight to the iss.

  #4  
Old August 11th 12, 03:39 AM posted to sci.space.station
Greg \(Strider\) Moore
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Default Express supply..

"Korben Dallas" wrote in message ...

On 8/5/2012 1:51 AM, Brian Gaff wrote:
Now they can resupply in 6 hours, one assumes only if the orbit and pad
are
in the correct relationships, it seems that its not that difficult after
all. I'm sure the old reason for not doing this was due to excessive fuel
use to achieve it in relation to the more leisurely way. Was or is this
true, or was it just an excuse?


the old obstacle for doing this was lower iss orbit. the iss orbital
altitude was intentionally reduced to make it reachable by space shuttle.
now, with shuttle out of the picture, the iss was transferred to a notably
higher orbit, making it much easier to shoot progress ships straight to the
iss.


Cite for that? Since August of last year to to now it's gone from about 382
kilometers to approximately 402 kilometers, a 20km boost.

During the shuttle supported part of program height ranged from
approximately 332 km to as high as 400 km.

I'm not sure 402km is "substantially higher"

And I'm not clear how that would make it easier for Progress (which would
suffer similar upmass losses at higher altitudes).

Thanks.



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  #5  
Old August 11th 12, 05:42 PM posted to sci.space.station
snidely
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Default Express supply..

JF Mezei was thinking very hard :
Greg (Strider) Moore wrote:

During the shuttle supported part of program height ranged from
approximately 332 km to as high as 400 km.


This in itself isn't enough information. Consider the case where the
400km was achieved only while the shuttle was grounded, and during
normal shuttle ops, the altitide varied much less above 332.

And if they no longer have to let the ISS altitide drop to allow shuttle
visits, it would mean fewer reboosts since the station would be staying
at higher altitude where there is less drag.

Average altitude might be a better metric to compare ISS during and
after shuttle.


And I'm not clear how that would make it easier for Progress (which would
suffer similar upmass losses at higher altitudes).


My guess is that it is fuel savings that are factored in of there need
to be fewer reboosts.


I seem to recall that the Shuttle was giving bigger reboosts to ISS
than could be done with other means. Perhaps the average altitude was
raised because the big boot ... er, boost ... wasn't available
anymore.

/dps

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  #6  
Old August 11th 12, 06:46 PM posted to sci.space.station
Brian Thorn[_2_]
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Posts: 2,266
Default Express supply..

On Fri, 10 Aug 2012 22:10:44 -0400, JF Mezei
wrote:


With the higher ISS altitude, and the lowest acceptable progress
altitude after launch, assuming worst case scenario for position of ISS
at progress launch time, how long would it take for the progress to lap
the station to get itself into the right position to raise orbit to ISS'
and dock without delay ?

aka: with the techniques used for the 6 hour launch-to-dock, what is the
worst case scenario ? 7 hours ? 12 hours ? 24 hours ?


If I recall correctly, it was reported it could be either a 6 hour
rendezvous or a standard 50-ish hour rendezvous, but there wasn't any
in-between.

Brian
  #7  
Old August 11th 12, 06:53 PM posted to sci.space.station
Brian Thorn[_2_]
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Posts: 2,266
Default Express supply..

On Fri, 10 Aug 2012 17:24:47 -0700, Korben Dallas
wrote:

the old obstacle for doing this was lower iss orbit. the iss orbital
altitude was intentionally reduced to make it reachable by space
shuttle. now, with shuttle out of the picture, the iss was transferred
to a notably higher orbit, making it much easier to shoot progress ships
straight to the iss.


I think the altitude difference has actually been pretty marginal
since the Shuttle's return to flight in 2005/2006. They did let the
Station get a little lower than normal for a couple of the real
heavyweight flights like Kibo and S6, but that wasn't constant.

There were several reports at the time of the launch that it was the
new TsVM-101 digital flight computer (introduced on Soyuz TMA-01M in
Oct 2010) that made this possible. Now that the TsVM-101 computer has
a few flights under its belt, Russia was ready to try rapid
rendezvous.

Brian
 




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