Re: record-breaking human achievement

From: Björn Gimle (b_gimle@algonet.se)
Date: Wed Aug 27 2003 - 15:57:16 EDT

  • Next message: Kurt Dequick: "raduga 33"

    It is not necessary, like in some replies, to use a program specifically
    built for these computations, and/or providing 9+ digits accuracy for the
    absolute distance.
    
    I don't have the data for Apollo missions, but for ground, aircraft and
    ISS standard prediction software plus simple estimates are sufficient.
    
    Using a point 6375 km below the sub-Martian point, SkyMap shows me ISS
    19.5 degrees from Mars, at a range of 6767.8 km at 10:02:50 (somewhat
    stale elset).
    With the cosine of 19.5, I get 6377.6 km along the Mars vector, ie 2.6 km
    above Earth's surface, so no mountain close to this location is high
    enough.
    
    I also plotted a more normal view (but 1 km above to account for
    mountains on nearby Tahiti)
    This shows that pass just 0.2 degrees above horizon, at a range of 2303
    km, corresponding to about 8 km. At first sight this should be refraction
    in this (stereographic=alt/az) plot mode, but I had expected more (.5
    degrees = 20 km extra?)
    
    To check for the effect of small time errors, it is sufficient to get
    three distances and use a quadratic approximation through them. The same
    technique can be used for satellites (conidering the slight change in
    radius due to orbital eccentricity), aircraft, and rotation of Earth's
    surface.
    
    I have from JPL Horizons for Mars:
     2003-Aug-27 09:00     55757931 km
     2003-Aug-27 10:00     55757921 km
     2003-Aug-27 11:00     55757948 km
    so the small precession in RA of the ISS orbit (~30 km/orbit) will at
    most produce 10 km along the Mars vector (at 19.5 degree distance), so
    Mars' movement will negate the gains. Likewise, a small shift along Earth
    or ISS' orbit will not reduce the distance significantly.
    
    
    
    
    ----- Original Message ----- 
    
    > It occurs to me that tomorrow, August 27th, some human may have a
    chance
    > to pass closer to Mars than anyone else in recorded history.  This
    could
    > be someone at or near the sub-Martian point or someone on ISS.
    > According to a very quick calculation based on a recent elset, this
    last
    > might occur at about 2003-08-27 1005 UT.  Or possibly some astronaut on
    > a previous mission, especially an Apollo mission.
    
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