NROL-52 results of initial observations

From: Ted Molczan via Seesat-l <>
Date: Sun, 15 Oct 2017 18:47:44 -0400
NROL-52 was launched from CCAFS on an Atlas V-421 on 2017 October 15 at
07:28 UTC. I believe that its payload is the second of a new generation of
SDS (aka Quasar) communication relay. It is likely to be catalogued as USA
279 (2017-066A).

1. Observations

We had excellent tracking of the initial orbit, thanks to Paul Camilleri,
who is ideally placed to observe many of the types of launches that interest
us. He observed and imaged the payload on 2017 October 15, between 11:34 UTC
and 12:57 UTC, and the Centaur from 11:28 UTC to 14:56 UTC. His observations
are here:

I found the time of the final two Centaur points to be one hour late,
perhaps due to a typo. Subtracting 1 h yielded good residuals within the
differential correction.

2. Payload orbital elements in GTO

The residuals between the observations and estimated pre-launch elements
were about 0.01 deg cross-track, and about 10 s to 20 s in time. The object
appeared to be falling very gradually behind prediction in time, which
suggested a bit higher orbit than estimated.

For the orbital analysis, I propagated the pre-launch estimated TLE to the
start of the observations. I differentially corrected it in two different

For the following TLE, I adjusted only the mean-anomaly:

USA 279                                               1113 X 35802 km
1 76402U 17066A   17288.48263889  .00000000  00000-0  00000-0 0    06
2 76402  18.6773 325.4984 6983839 178.5905 121.9313  2.21873127    02
Arc 20171015.48-1015.54 WRMS resid 0.022 totl 0.011 xtrk

To account for the possibly higher orbit, I adjusted only the mean motion to
produce the following TLE:

USA 279                                               1134 X 35924 km
1 76402U 17066A   17288.48263889  .00000000  00000-0  00000-0 0    06
2 76402  18.6773 325.4987 6983832 178.5899 122.0404  2.20915106    06
Arc 20171015.48-1015.54 WRMS resid 0.006 totl 0.004 xtrk

The above TLEs should bracket the actual position until the object

3. Centaur de-orbit

The Centaur's MES3 burn at approximately 08:33 UTC (MET 01:05) put it on a
trajectory to de-orbit about 750 km south of Hawaii.

I obtained the following orbital elements from Paul's observations:

Centaur                                               -244 X 28046 km
1 76403U 17066B   17288.47777778  .00000000  00000-0  00000-0 0    03
2 76403  18.8913 323.6165 6975099 166.6469 161.4027  3.00742648    06
Arc 20171015.48-1015.62 WRMS resid 0.005 totl 0.002 xtrk

I used GMAT 2017a (General Mission Analysis Tool) to propagate the above TLE
to re-entry. A kmz file containing the final portion of the resulting
trajectory is here:

The following graphic was generated using the kmz file:

The white rectangle is the NOTAM hazard zone. Hawaii is just visible on the
horizon, 750 km to the north. The re-entry impact zone was an approximately
160 x 600 km rectangular region, centred near 11.87 N, 154.63 W.

The depicted re-entry trajectory begins at about 1000 km altitude. The
alternating red and white line segments span 5 s of flight.

The TLE propagated to theoretical impact within the NOTAM boundaries, near
11.92 N, 155.62 W, at about 15:57 UTC - 12 min. after the start of the NOTAM

The Centaur reached a maximum velocity of nearly 10.2 km/s inertial (not far
below escape velocity), 9.7 km/s relative the atmosphere. Maximum
deceleration of about 44 G occurred at about 49 km altitude. Nearly all
horizontal velocity had been lost by 30 km altitude, following which any
surviving debris would have fallen almost vertically. The final vertical
descent is clearly depicted in the above graphic.

The GMAT scripts used to propagate the TLE, and the Excel ephemeris
spreadsheet used to analyze the results and produce the kml file, are here:

Both scripts begin with a state vector generated by the TLE. Version #1
covers the complete descent; #1a covers only the portion down to about 88 km
altitude, but at higher time resolution. I combined the output of both and
extracted data at approximately 5 s intervals.

Ted Molczan

Seesat-l mailing list
Received on Sun Oct 15 2017 - 17:48:32 UTC

This archive was generated by hypermail 2.3.0 : Sun Oct 15 2017 - 22:48:32 UTC