North Korea satellite: identity of catalogued objects

From: Ted Molczan (
Date: Fri Dec 14 2012 - 15:35:08 UTC

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    I have been trying to determine the identity of the objects launched by North Korea.
    USSTRATCOM has released TLEs of four objects, three of which have catalogue entries:
    12072A 39026 KMS 3-2
    12072B 39027 UNHA 3 R/B
    12072C 39028 UNHA 3 DEB
    12072D 39029 UNHA 3 DEB
    The decay rates of the 12072A, B and C TLEs were unrealistically high during the first day or so, but have since begun
    to settle down to what are probably more reasonable values.
    The elements of 12072A and B were swapped on the first day in orbit, but I am beginning to suspect they should not have
    been. Their orbits nearly intersect near the point of orbital insertion, which was near perigee. Their perigee heights
    are nearly identical, but the apogee of 12072B is 7 km greater than that of 12072A. Regardless of the mechanism of their
    separation, the payload might have been expected to have the higher apogee. If it was pushed from the rocket, then the
    extra velocity at perigee would have raised its apogee. Had separation motors on the rocket fired instead, then their
    retrograde thrust would have lowered its apogee. Either way, the payload would end up with the greater apogee. So 12072B
    seems more likely to be the payload, and 12072A the rocket.
    I am uncertain of the identity of 12072C and 12072D. One possibility is separation motor covers. Separation motors are
    mounted on the rocket, and fire retrograde. They are canted away from the velocity vector so that their plumes do not
    impinge upon the payload. As a result, when they fire, their covers are blown into orbits slightly out of the plane of
    the rocket and payload, and with a greater apogee - sometimes hundreds of kilometres greater. 12072C and D are partially
    consistent with this, in that they are offset in inclination from 12072A and B by about +0.04 deg and -0.04 deg,
    respectively; however, their apogee is actually somewhat less than that of 12072B, which I presume to be the payload.
    Also, their inclination offsets are quite a bit less than I see with Russian and Chinese separation motor covers.
    Alternatively, I wonder whether 12072C and D could be de-spin masses? If the rocket employs a solid motor, then it would
    likely have been spin-stabilized during firing. For the payload not to be spinning when it separates, the rocket must
    first de-spin. One method is to release a couple of small masses attached to the rocket by wires wrapped around its
    circumference. This is commonly called "yo-yo de-spin". The masses may be released and enter independent orbits. 
    I have never paid much attention to de-spin masses. Quite a few seem to be in orbit, which may aid in evaluating 12072C
    and D. Jonathan McDowell lists many in his excellent satellite catalogue, some with question marks:
    I have been looking for examples that might be similar to the 12072A-D objects. The TIP 3 related objects (1976-089A-D)
    may be useful. 76089A is the payload; B is the rocket. Both were inclined 90.3 deg. 76089C and D - the suspected de-spin
    masses - were offset in inclination -0.1 deg and +0.1 deg, respectively. Both had apogee not much different from that of
    payload and rocket.
    Nova 3 (1984-110A-D) may be another comparable case. The payload was inserted into a transfer orbit, which it later
    circularized, but the its Star 20 solid motor (object B) and de-spin masses (C and D) remained in substantially the
    transfer orbit. C was offset in inclination +1 deg; D was -0.4 deg. Apogee of both was about the same as that of the
    RADCAL (1993-041A-D) also seem comparable. C and D - the suspected de-spin masses - are offset in inclination from
    payload and rocket by -0.2 deg and +0.3 deg, respectively, with a modest effect on apogee (one decreased, the other
    12072C and D seem to be similar to the de-spin examples, in that their apogee was not changed appreciably. Separation
    motor covers tend to be ejected at higher relative velocity, often raising their apogee by hundreds of kilometres.
    Separation motor covers also tend to have a high area to mass ratio, leading to rapid decay. De-spin masses tend to
    decay much more slowly. 12072C and D appear to be relatively slow-decaying, with the caveat that their TLEs may not yet
    have converged to final values.
    If we can eventually make a confident determination whether C and D are separation motor covers or de-spin masses, it
    may help determine the method of propulsion of the rocket. In a brief search of the web, it seems that some say it
    employs a solid motor, some say liquid. De-spin masses are more likely to be associated with a solid motor stage.
    I am open to suggestions. Which one is the payload? Which one is the rocket? What are the C and D objects?
    Ted Molczan
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