Estimating decay rates

From: Sean Sullivan (seesat@golux.org)
Date: Sat Sep 21 2002 - 23:02:30 EDT

  • Next message: Tony Beresford: "Re: Estimating decay rates"

    Hi,
    
    I have a question about atmospheric drag, and it seems like someone here
    probably knows the answer, or can point me in the right direction ...
    
    I'm working on the Mars Gravity Biosatellite, planned for launch in 2005,
    flying about a dozen mice on a rotating spacecraft to study the effects of
    a partial gravity environment. This is a volunteer project involving MIT,
    U of Washington, and U of Queensland.  Since we have a re-entry capsule,
    this would be in low LEO -- possibly repeating groundtracks at mean motion
    16, or possibly slightly higher (up to about 15.75).
    
    We are trying to estimate propellant requirements for orbit adjustment
    under various strategies for handling drag and re-entry phasing.  The
    major unknown is a good estimate of the rate of altitude decay.  Also
    relevant is how this would increase if we were away from solar minima
    (making sure we can support a long launch delay without re-design).
    
    If there is empirical decay data out there, we can adjust for the
    differences in ballistic co-efficient.  I've seen the Starshine decay
    curve, but that was near solar maximum ... I've also seen ISS/Mir altitude
    graphs, but we're lower than these (well, lower than Mir was then ...)
    Something closer to our phase in the solar cycle would be helpful.  If
    there are atmospheric models that give atmospheric density, of course, we
    can do the math from there.
    
    I know that atmospheric drag is highly variable.  I'm not out for good
    predictions, just an average, and some sense of how much variance to
    expect in real life.  Anyone know of anything useful?
    
    If replying off the list, please use the address "mars at golux d.t org",
    which goes to my folder for this project.
    
    PS: for visual interest, this spacecraft will spin at about 30 rpm, so I'm
    hoping we can include a nice mirror!
    
    Sean Sullivan
    Lead engineer for Guidance, Navigation & Control
    Mars Gravity Biosatellite
    http://www.marsgravity.org
    
    
    
    
    
    
    
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