NROL-71 search elements

NROL-71 is scheduled for launch from VAFB on 2018 Dec 08 at 04:19 UTC, aboard a Delta IV-Heavy.

Justin Ray will live-blog the launch for ULA:

https://www.ulalaunch.com/missions/delta-iv-nrol-71

Stephen Clark will live-blog the launch for Spaceflight Now:

https://spaceflightnow.com/

Until a few days ago, I expected the payload to be the first Block 5 large electro-optical satellite of KH-11 heritage.
Doubts arose upon release of the launch time, which was inconsistent with either of the two established KH-11 orbital
planes. Doubts grew when the NOTAM revealed that NROL-71 is targeting, and its second stage will de-orbit from, an
approximately 74 deg orbit. KH-11 has always employed sun-synchronous orbits, inclined at approximately 97 deg or
98 deg, depending upon their altitude. This raised the possibility that the payload is something else, e.g. a
low-observable (aka stealthy) KH-11 variant, like Misty, which operated in quasi-65 deg orbits. I have insufficient
information to form an opinion that would aid in finding the payload. I am open to suggestions.

The following elements are consistent with the NOTAM information, on the assumption that the payload will initially be
in about the same orbit as the second stage. They are based on launch on 2018 Dec 08 at 04:19 UTC:

                                                         350 X 351 km
1 71901U          18342.18402778  .00000000  00000-0  00000-0 0    06
2 71901  74.0000 213.3000 0001000   0.0000 142.0000 15.72000000    03
                                                         259 X 442 km
1 71902U          18342.18402777  .00000000  00000-0  00000-0 0    06
2 71902  74.0000 213.3000 0136000 235.0000 269.0000 15.72000000    03
                                                         259 X 442 km
1 71903U          18342.18402776  .00000000  00000-0  00000-0 0    06
2 71903  74.0000 213.3500 0136000  55.0000  85.0000 15.72000000    05

                                                         503 X 504 km
1 71904U          18342.18402775  .00000000  00000-0  00000-0 0    06
2 71904  74.0000 214.0500 0001000   0.0000 142.0000 15.20000000    02
                                                         259 X 748 km
1 71905U          18342.18402774  .00000000  00000-0  00000-0 0    06
2 71905  74.0000 214.0500 0355000 235.0000 272.0000 15.20000000    09
                                                         259 X 778 km
1 71906U          18342.18402773  .00000000  00000-0  00000-0 0    06
2 71906  74.0000 214.0500 0376000  55.0000  85.0000 15.15000000    09

                                                         579 X 581 km
1 71907U          18342.18402772  .00000000  00000-0  00000-0 0    06
2 71907  74.0000 214.5000 0001000   0.0000 142.0000 14.95000000    06
                                                         259 X 870 km
1 70908U          18342.18402771  .00000000  00000-0  00000-0 0    05
2 70908  74.0000 214.5000 0440000 235.0000 271.0000 15.00000000    03
                                                         259 X 901 km
1 71909U          18342.18402770  .00000000  00000-0  00000-0 0    06
2 71909  74.0000 214.5000 0461000  55.0000  82.0000 14.95000000    01

Each TLE passes close to the launch site about 6.5 minutes after launch, and passes close to the centreline of the
second stage de-orbit zone. The orbits that meet these criteria are strongly dependent upon RAAN; the further east,
the greater the required mean motion.

There are three groups of TLE. Within each group, RAAN is constant or nearly so, but orbits vary in eccentricity and
argument of perigee. The first TLE in a group is circular.

If the payload is a KH-11, then given the disclosure that the new generation will retain the existing mirror diameter
of 2.4 m, its perigee height should be near the existing value of 259 km. Accordingly, the second and third TLE in each
group is elliptical, with that perigee height. The second TLE has argument of perigee near 235 deg, which results in
near apogee passes around latitude 50 N; the third one has perigee passes around 50 N.

The plane of the first group is a little west of the launch site about 6.5 minutes after launch; the middle group
roughly overhead; and the final group, a little west. Based on history, the final group seems more likely. I doubt
passes will be much earlier than the times of the first group, but I can imagine passes a bit later than indicated by
the final group.

I hope the above will prove to reasonably bracket reality. I am open to suggestions for other orbits.

This launch has already presented a huge surprise; there could well be more.

Happy hunting!
Ted Molczan



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