Rocket Body of Navid Satellite May be Venting Fuel

From: Ted Molczan (
Date: Wed Feb 08 2012 - 14:11:19 UTC

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    Joseph Remis alerted the list to the unusual orbital evolution of the rocket body 12005B / 38076, that placed the Navid
    (12005A / 38075) satellite into orbit:
    Joseph noticed that its eccentricity has been increasing, when it should have been decreasing. Bob Christy noted that
    the Navid satellite is not experiencing this perturbation, despite being in substantially the same orbit:
    This morning, I have taken a preliminary look at the orbital evolution of both objects, based on the TLEs issued by
    USSTRATCOM. Navid's orbit appears to be evolving about as expected, but its rocket's eccentricity and argument of
    perigee are evolving significantly differently. Below is a comparison of rate of change of several of the elements,
    determined through linear regression over the span of TLEs issue to-date. The coefficient of determination (r^2) is in
                          12005A           12005B
    Inc deg/d (r^2)   -7.89E-4 (0.68)  -1.24E-3 (0.77)
    RAAN deg/d (r^2)  -4.68E+0 (1.00)  -4.69E+0 (1.00)
    Ecc /d (r^2)      -4.10E-5 (0.97)  +1.29E-4 (0.86)
    AOP deg/g (r^2)   +2.21E+0 (1.00)  +1.72E+0 (1.00)
    12005A's orbit appears to be evolving about as expected. For example, its argument of perigee (AOP) is precessing +2.21
    deg/d, compared with 2.35 deg/g per the SGP4 orbital model upon which the TLEs are based. 12005B should be precessing at
    nearly the same rate, but its actual rate is about 0.5 deg/d less than that of its payload. As already noted, 12005B's
    eccentricity should be decreasing due to the effects of drag, but it is actually increasing. A cursory look at the data
    indicates that the semi-major axis is being stretched at both ends, i.e. perigee decreasing and apogee increasing, but
    that is subject to confirmation.
    LEO orbits near the inclination of this orbit are known to experience gravitational perturbations not modelled by SGP4
    that could cause some of these symptoms, but since both objects are in nearly the identical orbit, that cannot explain
    the difference in their evolution. Since only a few days have passed since launch, venting of residual fuel may be the
    cause, and I find evidence for this in the rapid spin observed by Alberto Rango, Brad Young and Alexander Repnoy:
    Brad and Alberto managed to measure the flash period, which averaged about 0.6 s, indicative of a very rapid spin, that
    can result from fuel venting. The venting could be intentional or due to leakage; I suspect the latter, since
    intentional venting typically is accomplished rapidly - in a matter of minutes, not days. If venting is the cause, then
    the unusual orbit perturbation will cease once the fuel has been depleted. If it persists for a long time, then we may
    need to consider a more exotic explanation, like intentional low-thrust manoeuvring, but that would be more difficult to
    reconcile with the rapid spin, that is probably an end over end tumble.
    Ted Molczan
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