Unusual TLEs (for escaping object)

From: Bill Gray via Seesat-l <seesat-l_at_satobs.org>
Date: Sun, 18 Aug 2019 16:09:14 -0400
    Thought some on this list might be interested in the following.

    I've been generating TLEs for a few "unusual" objects
recently not tracked by Space-Track,  including the Spektr-RG
X-ray/gamma-ray observatory and its booster.  The observatory
itself will,  we hope, go out to the Earth-Sun L2 point,
about 1.5 million km away, and stay there (with the aid of
occasional small maneuvers).  The booster will go out there
and just keep going into a heliocentric orbit.  We won't see
it again until June 2038,  after it's completed 18 orbits
around the sun and we've completed 19 :


    Fitting TLEs to an object that's headed into heliocentric
orbit has some odd consequences.  The TLEs for this object are at


    with one TLE fitted for each day,  up to October 1.  At
that point,  the nominal eccentricity reaches one,  and the
mean motion (see the last TLE at the above page) reaches
0.00003600 revolutions/day,  for an "orbital period" of
about 76 years.  Not that the object will actually do that,
of course.  But you do get a TLE that models the motion of
the object to an accuracy of about 80 km,  at a point where
it's nearly three million kilometers away.  I think this
must be a record for a "TLE-able" object.

    Note that these TLEs may or may not work for you.  With
objects like these,  you have to use SGP4 for an object that
is undeniably not in a 225-minute or less orbit.  If your
software pays attention to the "ephemeris type" flag in a
TLE,  you'll be okay :


    If it assumes the "ephemeris type" is always zero or blank,
these TLEs won't work for you.  They'll definitely stress-test
your programs,  though.

-- Bill
Seesat-l mailing list
Received on Sun Aug 18 2019 - 15:10:04 UTC

This archive was generated by hypermail 2.3.0 : Sun Aug 18 2019 - 20:10:04 UTC