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Drag on ISS



 
 
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  #1  
Old November 11th 04, 11:03 PM
Allen Thomson
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Default Drag on ISS

Anybody know why the mean altitude has been decreasing somewhat
rapidly in the past while?

http://www.heavens-above.com/issorbitheight.asp

Solar activity? Orientation?
  #2  
Old November 11th 04, 11:11 PM
Ted Molczan
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"Allen Thomson" wrote in message
om...
Anybody know why the mean altitude has been decreasing somewhat
rapidly in the past while?

http://www.heavens-above.com/issorbitheight.asp

Solar activity? Orientation?


Probably due to the intense geomagnetic storm during Nov 8-10.

Ted Molczan


  #3  
Old November 13th 04, 12:31 AM
hop
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(Allen Thomson) wrote in message . com...
Anybody know why the mean altitude has been decreasing somewhat
rapidly in the past while?

http://www.heavens-above.com/issorbitheight.asp

Solar activity? Orientation?


Solar activity:
http://www.spaceref.com/news/viewsr.html?pid=14469

"After yesterday's dramatic drop in ISS altitude due to an energetic
solar particle event with 100MeV protons (measured on the GOES 11
satellite), resulting in a massive spike in geomagnetic activity and
in atmospheric drag at orbital altitude, solar activity appears to
have leveled off and come down, with reduced orbital decay. The crew
was not in any danger. [Yesterday's drop in mean flight altitude
reached ~440 m in 24 hrs, as compared to previous ~160 m/day. This
morning, the 24-hr. drop was ~200 m. Next week's planned reboost
(11/17) will make up for the loss.]"

A nice demonstration of just how variable the upper atmosphere is.
  #4  
Old November 14th 04, 10:45 PM
Explorer8939
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There is a lower altitude bound (about 300 km or so) after which a
single Progress or Shuttle cannot reboost ISS enough to counteract the
increased drag at that altitude. Given that the Russians can't make a
lot of Progresses these days, the Shuttles and ATV aren't flying, the
reality is that a few weeks of bad solar weather could put the whammy
on the whole program.
  #6  
Old November 15th 04, 07:13 PM
John Doe
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Allen Thomson wrote:
ISS carries a fuel reserve about ten times as large as a Progress

delivery. That would let it do a major reboost back to ~400 km
altitude even without the Progresses.


We know they can transfer fuel from Progress to the station.

But in such an event, could they transfer fuel from station to Progress so
that they can use the Progress engine instead of the Stations's thrusters ?
  #7  
Old November 16th 04, 12:49 AM
Chris Bennetts
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John Doe wrote:

We know they can transfer fuel from Progress to the station.

But in such an event, could they transfer fuel from station to Progress so
that they can use the Progress engine instead of the Stations's thrusters ?


I believe so. I seem to recall that, if they want to use the Progress's
main engines, they need to do a transfer before the burn, but if they
use the Progress's smaller attitude control thrusters for the reboost,
they can feed fuel straight from the station's tanks during the burn.

--Chris
  #8  
Old November 16th 04, 02:13 AM
Tom Kent
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John Doe wrote in :

But in such an event, could they transfer fuel from station to
Progress so that they can use the Progress engine instead of the
Stations's thrusters ?


Maybe I'm missing something, but why would they want to? Is there
something wrong with the station's thrusters?
  #9  
Old November 16th 04, 02:40 AM
Explorer8939
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Well, not exactly. First off, the ISS "thrusters" are not too useful
for reboost. They are mainly used for attitude control, but are not
particularly useful for orbital changes. So, the ISS prop would have
to be burned by the Progress, in particular the mid-belt thrusters,
which aren't particularly good either for reboost.

But there are some other issues, as well. I have a vague recollection
that if the FGB prop tanks get too low, they can't be qualified for
long term storage of propellant any more. So, if too much of that 4
metric tons of prop is used for a major reboost, things could become
very difficult at ISS.

Lastly, if ISS gets too low, ie down about 300 km altitude, the
Progress thrusters may not be able to over come the drag, even if prop
is available. This may be because the thrusters cannot burn long
enough in one session without overheating.


(Allen Thomson) wrote in message . com...
(Explorer8939) wrote


There is a lower altitude bound (about 300 km or so) after which a
single Progress or Shuttle cannot reboost ISS enough to counteract the
increased drag at that altitude. Given that the Russians can't make a
lot of Progresses these days, the Shuttles and ATV aren't flying, the
reality is that a few weeks of bad solar weather could put the whammy
on the whole program.


Jorge Frank provided some good information on this a few months ago.
ISS carries a fuel reserve about ten times as large as a Progress
delivery. That would let it do a major reboost back to ~400 km
altitude even without the Progresses.

Lessee

Date Total fuel

2004-09-08 4408 kg [SM(552) FGB(3388) PRO M(468)]
2004-09-16 4158 kg [SM(552) FGB(3326) PRO M(280)]
2004-09-22 4109 kg [SM(552) FGB(3557) PRO M(0)]
2004-09-30 4109 kg [SM(552) FGB(3557) PRO M(0)]
2004-10-07 4083 kg [SM(552) FGB(3531) PRO M(0)]
2004-10-14 4076 kg [SM(552) FGB(3524) PRO M(0)]
2004-10-21 4060 kg [SM(552) FGB(3508) PRO M(0)]
2004-10-28 3998 kg [SM(552) FGB(3446) PRO M(0)]
2004-11-04 3951 kg [SM(552) FGB(3399) PRO M(0)]

 




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