NROL-71 search elements for 2019 Jan 19 19:10 UTC

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Sat, 19 Jan 2019 14:08:44 -0500
NROL-71 is scheduled for launch from VAFB aboard a Delta IV-Heavy on 2019 Jan 19 at 19:10 UTC.

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/2018/12/07/delta-382-mission-status-center/

I believe that the payload is the first Block 5 KH-11. My payload speculation post is here:

http://satobs.org/seesat/Dec-2018/0058.html

1. Planar window

The launch times published to-date reveal that the window is planar, i.e. targeting a specific plane or range of planes:

2018 Dec 08 04:19 UTC
2018 Dec 09 04:06
2018 Dec 19 01:57
2018 Dec 20 01:44
2018 Dec 21 01:31
2019 Jan 19 19:05

I am not aware of an existing satellite in orbit with which the payload could form a constellation or rendezvous, so I
am puzzled by the existence of a planar window.

Over 43 days, the window moved 554 min. earlier, or about 12.9 min/d.

The rate of precession of the RAAN is:

= 360 * (1.00273790934 - 1440/(1440 - 12.9))

= -2.27 deg/d

The rate of precession is a function of inclination, mean motion and eccentricity, so this is a strong clue to the
planned final orbit of the satellite.

Analysis of the NOTAM data reveals the target inclination to be about 74 deg. My guess is that the uncertainty is less
than 0.5 deg.

The rate of precession is much more sensitive to inclination than to mean motion and eccentricity; therefore, even a
small uncertainty in inclination results in a large uncertainty in mean motion.

Below are the mean motion and eccentricity that yield -2.27 deg/d RAAN precession, that bracket the range of
inclination:

Inc     n0       e0     Per  Apo
73.5  15.5095  0.02246  259  564
74.0  15.7143  0.01386  259  446
74.5  15.9268  0.00498  259  325

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, which I used to constrain the above estimates.

The initial orbit could be a little lower or higher than tabulated above. The last two KH-11s made small apogee boosts a
few days after launch.

2. Visibility windows

Based on limited checks, it appears that about 5 days after launch, morning visibility will open for far northern
observers, and evening visibility will open for mid-southern latitude observers. Prospective observers should check for
local visibility.

3. Search elements

The search elements are based on launch on 2019 Jan 19 at 19:10 UTC.

I intend to issue revisions in the event of material new information or launch delays.

There are pairs of TLEs for inclination 74.5 deg, 74 deg, and 73.5 deg. In each pair, one TLE has argument of perigee
that yields apogee passes near mid-latitudes; the other has argument of perigee that yields perigee passes. This is
intended to help bracket the minimum and maximum predicted elevation above the horizon.

Each TLE is labelled to indicate whether it yields apogee or perigee passes at mid-northern latitudes. Southern
hemisphere observers can use the same TLEs by swapping the apogee and perigee labels.

The RAAN of each TLE could be off by at least 1 deg. Along-track prediction time uncertainty is at least a couple of
minutes.

apogee                                                   259 X 325 km
1 71907U          19019.80312496  .00000000  00000-0  00000-0 0    00
2 71907  74.5000 117.3421 0049782 323.0000 181.3000 15.92677149    03
perigee                                                  259 X 325 km
1 71908U          19019.80312495  .00000000  00000-0  00000-0 0    00
2 71908  74.5000 117.3671 0049782 110.0000  33.8000 15.92677149    06
apogee                                                   259 X 446 km
1 71909U          19019.80312494  .00000000  00000-0  00000-0 0    00
2 71909  74.0000 118.1121 0138590 305.0000 199.5000 15.71434437    01
perigee                                                  259 X 446 km
1 71910U          19019.80312493  .00000000  00000-0  00000-0 0    01
2 71910  74.0000 118.1471 0138590 115.0000  28.2000 15.71434437    08
apogee                                                   259 X 564 km
1 71911U          19019.80312492  .00000000  00000-0  00000-0 0    01
2 71911  73.5000 118.9121 0224609 305.0000 199.6000 15.50949585    06
perigee                                                  259 X 564 km
1 71912U          19019.80312491  .00000000  00000-0  00000-0 0    01
2 71912  73.5000 118.9321 0224609 125.0000  18.0000 15.50949585    03

This launch has already presented a huge surprise in the orbital inclination; there could well be more.

Happy hunting!
Ted Molczan


_______________________________________________
Seesat-l mailing list
http://mailman.satobs.org/mailman/listinfo/seesat-l
Received on Sat Jan 19 2019 - 13:11:13 UTC

This archive was generated by hypermail 2.3.0 : Sat Jan 19 2019 - 19:11:13 UTC