NROL-101 payload speculation

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Wed, 4 Nov 2020 14:33:55 -0500
NROL-101 is scheduled for launch on 2020 Nov 04 at 22:54 UTC, from Cape Canaveral, aboard an Atlas V-531 with a medium
length fairing.

The NOTAMs reveal that the target orbit is high inclination. I estimate at least a 57 degree parking orbit, perhaps a
few degrees higher.
 
The launch time on Nov 4 is 4 minutes earlier than that of Nov 3, which is consistent with a planar launch window of a
Molniya orbit.

I may post search elements later today.

Historically, U.S. Molniya missions have been SIGINT (signals intelligence) or SDS relay satellites.

1. Timing favours SDS

The U.S. SIGINT satellite constellation in Molniya orbits consists of three Trumpet spacecraft launched in the 1990s,
and four follow-on spacecraft launched since 2006. All seven satellites remain in operational orbits. The last pair of
follow-ons went up in 2014 and 2017. This year seems too soon for a replacement or new generation.

Since 1990, SDS relay satellites have operated in geosynchronous, as well as Molniya orbit. The operational
constellation in Molniya orbit consists of two 3rd generation spacecraft, launched in 2004 and 2007. 

The first two fourth generation SDS were launched in 2016 and 2017 to geosynchronous orbits. I suspect they are
optimized for the Block 5 KH-11, the first of which went up in January 2019, and the second of which is due for launch
in a few months. The long period without the launch of a new SDS to Molniya orbit has led to speculation that the
Molniya orbit is being phased out in favour of a solely GEO constellation. If fourth generation Molniya SDS are planned,
then they seem about due for launch. This makes it easier to argue that the payload of NROL-101 is an SDS, especially
given that 2020 seems too soon for a new Molniya SIGINT.

2. Historical launch site preference favours SDS

Historical launch site preference also favours SDS over SIGINT for NROL-101. Molniya SIGINTs have launched from VAFB,
except for the three Trumpets in the 1990s. All SDS have launched from Cape Canaveral since 1989. If these preferences
remain, then the payload of NROL-101 most likely is an SDS.

3. Medium 5 m fairing consistent with 4th generation SDS

NROL-61 and NROL-52, which launched the first two fourth generation SDS to GEO, employed 4 m XEPF fairings. If
NROL-101's payload is the same, then why does it employ a medium 5 m fairing?

I speculate that the diameter of NROL-101's fairing may have been determined by Centaur manoeuvre requirements, not
payload dimensions. Certain GEO missions use the Centaur stage for all three major burns: achieve LEO parking orbit,
GTO, and final burn to GEO. That final burn occurs more than 6 h after launch, which for Atlas V requires a Centaur
outfitted with an Extended Mission Kit (aka GSO Kit). According to the payload user's guide, the only Atlas V models
with Centaurs so equipped are 521, 531, 541 and 551. 

NROL-101 is not headed to GEO, but could there be a need to fire its Centaur 6 hours or later after launch? For example,
to deploy an additional payload into a different orbit? Or might it make one rev after SDS deployment, and then burn
into a solar system disposal orbit at the next perigee? That would explain the absence (to-date) of a de-orbit NOTAM.
This is all speculation, unsupported by technical analysis of mission requirements.

I cannot explain the use of the 5 m fairing on NROL-101, but its medium length is consistent with the 4 m XEPF fairings
used to launch 4th generation SDS to GEO.

In the Atlas V User's Guide, Figs. 6-3 and 6-4 depict Simplified Static Payload Envelopes of the 4 m and 5 m PLFs,
respectively. The height of the payload envelope of the 4 m EPF and XEPF are 10.31 m and 11.23 m, respectively. That
suggests that the fourth generation SDS requires more than 10.31 m. The 5 m short PLF can accommodate 10.18 m, which
would be too short. The 5 m medium PLF can accommodate 12.93 m, which would be more than adequate. 

Somewhat different information appears in Figs. 6.1-2 to 6.1-4 for the 4 m PLF, and Fig. 6.2-1 for the 5 m PLF, but it
leads to the same conclusion. The height of the payload envelope of the 4 m EPF and XEPF are 10.65 m and 11.57 m,
respectively. That suggests that the fourth generation SDS requires more than 10.65 m. The 5 m short PLF can accommodate
9.85 m, which would be too short. The 5 m medium PLF can accommodate 12.59 m, which would be more than adequate.

From both sets of figures, I conclude that if a fourth generation SDS were to be launched under a 5 m PLF, then it would
need to be the medium length version. NROL-101's use of the medium 5 m PLF would be consistent with a fourth generation
SDS.

4. Loose ends

The SDS hypothesis is not without problems.

NROL-101 does not appear to be targeting either of the existing SDS planes, but I am not certain that it needs to.

NROL-101 reportedly was switched from Atlas V-551 to V-531, which I cannot explain.

5. Feedback

I am interested to know of any problems with the above analysis. Alternatives are welcome.

Ted Molczan


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Received on Wed Nov 04 2020 - 19:33:55 UTC

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