Re: ISS Boost?

From: John A. Dormer 2 (
Date: Sun Jul 12 2009 - 23:18:30 UTC

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    It's not a precise answer, but it may be a case where the Shuttle is
    passively using its normal on-orbit adjustments to boost the Station. I
    think this has been covered on the list once about two years ago.
    The way it would work is that the Shuttle's onboard Inertial Navigation
    System feeds data to the flight control system, which calculates that
    it's not in the right place in space at a particular time vs. the orbit
    it should be in. The system then issues a corrective burn to try to get
    to that place. As a consequence of programming a particular new set of
    orbital parameters to match, which aren't the same ones used to
    rendezvous with the Station, both machines gradually get into the
    second, target orbit.
    From what I remember, the process can take several days, but it's
    possible to use specific, larger burns to boost the station as well.
    That'd just be a matter of "plugging in" a more-mismatched target orbit
    and letting the machinery do the rest.
    Requesting an orbit which is too deviant might result in oscillations
    which can't be physically solved without some wild rides, so I'm certain
    that there are astrodynamicists on the ground who work to be sure that
    the current and requested orbits are conformable.
    	John wrote:
    > This is a forwarded question from a friend of  mine in Maryland.  If anyone 
    > on the list has an answer, let me know and I  will pass it along to him.  
    > Many Thanks!  -- joe  rao
    > -------------------------------------------------
    > I'm curious  if you have seen any news about whether NASA plans to do an 
    > ISS boost during  STS-127?
    > I was looking ahead to sighting opportunities for the ISS and  Endeavour in 
    > the DC area, hoping we might get a chance to see them shortly after  
    > undocking on Flight Day 15.  (Yesterday's scrub unfortunately appears to  have 
    > left only one chance for that here -- Sunday, July 26; had they been able  to 
    > launch yesterday, Saturday, July 25 would have been Flight Day 15 and so both 
    >  Saturday and Sunday might have been good chances.)  
    > In the process,  I happened to look at Heavens-above's chart of the ISS's 
    > orbit elevation  ( and it didn't 
    > seem that the ISS  had been significantly boosted since January.  I searched 
    > Google and found  a couple postings on SeeSat, one of which indicated a 
    > planned boosting for this  past February had been canceled and another of which 
    > led me to a Jim Oberg  article about the scary moments of (apparently) the 
    > last ISS boost  ( In it he said NASA 
    > had decided to delay  further boosting the ISS because it would help save 
    > propellant in view of the  2JA mission, which, if I understood the quote 
    > correctly, the ISS needed to be  somewhat lower for.  Further research showed 2JA 
    > is, lo and behold,  STS-127.
    > Well, it's now seven months since the last significant boosting  for the 
    > ISS (going by the H-A chart above), which led to my question -- are they  
    > planning to boost the ISS's orbit during STS-127?  But none of the STS-127  
    > mission timelines I've found say anything about using Endeavour to boost the  
    > ISS.  Since, from what I've read, only the shuttle and the ATV are capable  of 
    > significantly boosting the ISS orbit (and I've seen no mention of another 
    > ATV  launch any time soon, and they're running out of shuttle launches), I 
    > would have  thought they'd do a reboost during STS-127.  But I can find 
    > nothing on the  subject.  
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