Fragmentation of 91082A (DMSP B5D2-6)

From: Ted Molczan (molczan@rogers.com)
Date: Thu May 27 2004 - 12:45:41 EDT

  • Next message: Greg Roberts: "Obs 26 May 2004"

    USSTRATCOM has catalogued 56 new pieces of debris from the weather satellite
    DMSP B5D2-6 (91082A / 21798). They span 1991-082F / 28294 to 1991-082BN / 28349.
    No elements are available, and none are likely to be published.
    
    Hobbyists are the only public source of orbital elements of this object.
    
    The last pre-break-up elset is of epoch 2004 Apr 14:
    
    DMSP B5D2-6      6.4  1.7  0.0  6.6 v 5.43
    1 21798U 91082A   04105.69574099  .00000150  00000-0  76795-4 0    03
    2 21798  98.6774 128.2477 0011500  16.4304 343.5695 14.15516896    07
    
    On 2004 May 03 UTC, Paul Gabriel observed 91082A or a related object near the
    predicted path of 91082A:
    
    http://satobs.org/seesat/May-2004/0018.html
    
    It was 24.21 s early, and 0.22 deg off the track predicted by the above
    elements, taking into account Earth's rotation during 24.21 s. This is a large
    difference, given that the elements were only 18 d old.
    
    The object was 25 deg above the horizon, which is not all that high, so to be
    0.22 deg off-track suggests that the break-up may have imparted significant
    velocity.
    
    91082A's orbit is sun-synchronous, so its visibility window is seasonal - during
    the Northern and Southern hemispheres' respective winters.
    
    Weather permitting, it would be worthwhile performing a planar search for
    debris.
    
    I can only speculate as the to the cause of the fragmentation. Shortly after
    launch, DMSPs (and their NOAA cousins), use hydrazine thrusters to trim their
    orbit, after which they are made inoperative. Unspent hydrazine has been the
    cause of numerous satellite fragmentations. I do not recall any other break-ups
    of DMSPs or NOAAs.
    
    The NOAA/DMSP Propulsion and Reaction Control Subsystem is described here:
    
    http://www2.ncdc.noaa.gov/docs/klm/html/c1/sec12-3.htm
    
    "The hydrazine RCE consists of four thrusters and two spherical storage tanks
    The hydrazine thrusters are used for maneuvers requiring large control torques
    and for all velocity change maneuvers, i.e., spacecraft separation from the
    booster and orbit circulation trim, as well as pitch and yaw control during the
    AKM burn. After completion of the orbital velocity trim burn, pyrotechnic valves
    at the outlet of each hydrazine propellant tank may be fired to isolate the
    hydrazine thrusters from the propellant tanks and render the system inoperative.
    
    The cold-gas nitrogen RCE consists of eight thrusters and two spherical storage
    tanks of usable nitrogen. The nitrogen thrusters are used for three-axis control
    during ascent (except during AKM burn), Earth acquisition after handover and as
    a backup for momentum unloading in normal orbit mode control. Four of the
    thrusters provide roll control through Ascent Guidance Software (AGS), and are
    operated, under software control, in coupled pairs. The remaining four thrusters
    are operated individually to provide AGS pitch and AGS yaw control."
    
    Ted Molczan
    
    
    
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