Chandra and TDRS 4

From: Curtis Haase (
Date: Mon Feb 28 2000 - 10:05:41 PST

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    Some observations made on Sunday evening (local time) [UT date Feb 28]:
    I observed the Chandra spacecraft (99-040B, 25867) using a 10-inch
    reflector.  Chandra was low in the south, rising up after perigee
    passage less than an hour earlier.  Its brightness was consistent 
    with the 8th magnitude predicted using the standard magnitude of 3.0
    in the Mccants.tle file.  It was moving relatively slowly through the
    star field (about 1 degree per minute) so I was able to follow it and
    obtain a very good positional observation:  at 4:59:25.0 UTC Feb 28 2000
    Chandra passed directly over the 9th mag star SAO 178543 (J2000 position
    from GUIDE 7 is 10h13m07s, -30d11m56s).  A 10th mag star 1.4 arcmin to
    the NW made a wide double with the convergent Chandra and SAO 178543,
    so I estimate that the position given above is good to better than
    0.5 arcminute.  I continued to follow the spacecraft with the telescope
    for another 10 minutes as it slowly rose higher in the south.  Finally
    it dimmed as it began to enter eclipse, and it disappeared in the 10 inch
    at 5:10:17 UTC.
    My method for locating Chandra was to obtain a state vector from
    JPL Horizons (telnet to, port 6775), use VEC2TLE to
    convert it to an SGP tle, and then use the eleset with GUIDE 7 to
    plot the path through the starfield.  Chandra was running only about
    5 seconds late relative to the JPL horizons SSD ephemeris that was
    loaded on Feb 1st!  I have found the JPL ephemeris to be considerably
    more accurate than the predictions generated using NORAD elements from
    GSFC.  I also found that if you try to propagate the NORAD elset with
    the "original" SDP4 model (as you can find in Spacetrack Report No. 3)
    you will get large errors; but the NORAD elsets for Chandra give good
    agreement with the JPL ephemeris if you use SGP.
    Prior to the Chandra observations, I took a look at TDRS 4 (89-021B, 19883)
    with the 10 inch. For several minutes prior to entering eclipse the TDRS
    was VERY bright.  As it passed near 5th magnitude delta sextantis it was
    equal in brightness to that star.  It got even brighter (about 4th mag)
    and I could actually see it with the naked eye.  This was so unbelievable
    that I got out my 7x50 binoculars and watched the stars slowly drift past
    it to be sure I was really seeing the TDRS.  I switched back to the scope
    and observed TDRS 4 do a very slow fade and finally disappear in the
    10 inch at 2:31:13 UTC.  This was quite a site!
    Note: Observing site was the Texas Astronomical Society site in Atoka
    county, Oklahoma.  My postion was: long -96.1399 deg, lat 34.1844 deg,
    elev 0.170km.
            Curtis Haase
            Dallas, Tx
    PS: the generated Chandra elset I used is:
    1 25867U 99040B   00059.20759045  .00000000  00000-0  00000-0 0    09
    2 25867  29.9572 173.2996 7867482 287.8116   3.5344  0.37780175    03
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