Lacrosse 5: prospects for further manoeuvres

From: Ted Molczan (
Date: Wed May 04 2005 - 14:46:56 EDT

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    I have no idea whether or not there will be further manoeuvres, but there is a
    Lacrosse 4 made a small manoeuvre to further circularize its orbit, about 33 h
    after its first circularization manoeuvre. Unlike the first manoeuvre, the
    second one was nowhere near Diego Garcia, or any other tracking station I could
    Lacrosse 5's orbit is about 30 km higher than that of any previous Lacrosse.
    Perhaps it is intended to maintain some minimum required altitude over a
    potentially long service life in orbit. I note that Lacrosse 2 has decayed 32 km
    since it was launched 14 years ago.
    Lacrosse 5's higher orbit has an effect on its revisit rate with respect to
    targets on the ground. Previous Lacrosses nearly repeated their ground track
    every two days (29:2 resonance). Lacrosse 5 will nearly repeat its ground track
    every three days (43:3 resonance).
    I have insufficient information at this time to judge which of the above was the
    primary motivation for the higher orbit.
    If Lacrosse 5 manoeuvres again, I suspect its mean motion will decrease to
    between 14.5165 and 14.5232 rev/d. 
    A 14.5165 rev/d orbit would result in an exact 43:3 resonance; however, U.S.
    optical imagers almost never operate in an exact resonance. The lone exception
    was Misty 1, which operated in almost exactly a 127:9 and later a 43:3
    I arrived at the 14.5232 rev/d alternative, based on the apparently slightly
    greater than usual eccentricity of the present orbit - about 0.00086, instead of
    the more typical 0.0004; increasing the perigee height to achieve 0.0004
    eccentricity, would result in a 14.5232 rev/d orbit. Of course, this analysis is
    based upon the orbit I posted last night, which is based upon a fairly short
    A manoeuvre to a 14.5165 rev/d orbit would increase the orbital period by about
    7 s, causing the satellite to arrive about 100 s late 24 h after a manoeuvre.
    Ted Molczan
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