NROL-71 payload speculation

This post is my speculation about the payload and orbit of NROL-71. For my pre-launch search TLEs, please see:

http://satobs.org/seesat/Dec-2018/0045.html

I have long expected NROL-71 to launch the first Block 5 KH-11, and that has been the consensus among others who have
expressed their opinion. In this post, I will review the evolution of the NRO's imagery intelligence satellites since
the early 1970s, and discuss what the future may hold for KH-11, based on what is known about Block 5 KH-11, and recent
improvements in the resolution of commercial imagery.

The following table summarizes the evolution of the NRO's high-resolution and wide-area satellites since the early
1970s:

  Period           High-resolution satellite                  Wide-area satellite
----------   ------------------------------------    -------------------------------------
From   To    Program        Type       Resolution     Program        Type       Resolution
----  ----   --------  --------------- ----------    ---------  --------------- ----------
1971  1976   Gambit-3  Film-return        8 cm       Hexagon    Film-return       30 cm
1977  1984   Crystal   Electro-optical    7 cm       Hexagon    Film-return       30 cm
1985  2018   Crystal   Electro-optical    7 cm       Crystal    Electro-optical   28 cm

The following sections provide supporting information for each entry in the table.

1. 1971-1976

Gambit-3 (aka KH-8, after the designation of its camera) was a high-resolution satellite, of the film-return type. It
was first launched in 1966. It typically operated in an approximately 130 km by 400 km orbit. Its 1.1 m diameter mirror
had a theoretical resolution of about 8 cm at perigee, which was achieved in the early 1970s by upgraded versions of the
satellite. The NRO inadvertently confirmed this through a redaction error in a declassified copy of The GAMBIT Story,
which came to light in 2012, in the following NASASpaceFlight.com forum discussion:

https://forum.nasaspaceflight.com/index.php?topic=26821.80

The unredacted relevant quote:

"GAMBIT's contribution to scientific and technical (S&T) Intelligence were unsurpassed. The mature system produced
examples of imagery better than four inches ground-resolved distance (GRD). Furthermore, it exhibited excellent
mensuration capabilities, allowing the S&T photointerpreter to perform accurate measurements on foreign weapons
systems..." P.154

Remarkably, with Gambit-3, the NRO had already reached the limit on resolution imposed by atmospheric turbulence. Allen
Thomson informed me that scientific papers published in the mid-1960s by David Fried and, independently, by John C.
Evvard, revealed that atmospheric turbulence limits the imaging resolution achievable from Earth orbit to about 5 cm to
10 cm. Their papers are available at the following URLs:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690003603.pdf

https://www.osapublishing.org/abstract.cfm?id=53168

The significance of this, is that a larger mirror would not have improved the resolution of Gambit-3, at its minimum
altitude of 130 km. A larger mirror would only have been required if this distance were to be increased.

Hexagon (aka KH-9, after the designation of its camera), was the medium-resolution counterpart to Gambit-3. First
orbited in 1971, it was the last of the NRO's film-return spacecraft. Its theoretical resolution ranged between 20 cm at
perigee and 35 cm at apogee.

2. 1977-1984

The drag experienced by Gambit-3 was severe, which limited its orbital life; however, film-capacity was the main
determinant of its useful life. Once the film ran out, the spacecraft was useless. The need to return film to Earth for
processing, delayed the availability of imagery for analysis. An electro-optical imager would not have these
limitations.

Kennen (later changed to Crystal) (aka KH-11, after the designation of its camera), was the NRO's first electro-optical
spacecraft, first orbited in Dec 1976. Since it did not use film, its useful life was determined by the durability of
its hardware, and its ability to counteract the effects of atmospheric drag. Spacecraft maintain altitude against drag
by periodically firing thrusters to reboost their orbit, which consumes fuel. The higher the orbit, the lower the drag.
So, for a given quantity of fuel, the greater the orbital altitude, the greater the useful life.

KH-11 experienced far less drag than Gambit-3, by operating in a higher orbit. Its lowest altitude was about 250 km; its
greatest altitude was about 500 km. Since KH-11's minimum altitude was double that of Gambit-3, it needed a mirror
roughly double that of Gambit-3, to match Gambit-3's best resolution. The theoretical resolution of KH-11's 2.4 metre
diameter mirror at perigee was about 7 cm (3 inches) - about the same as Gambit-3 achieved with its 1.1 m mirror from
130 km.

Hexagon remained the wide-area satellite during this period.

3. 1985-2018

As the Hexagon program drew to a close in the early 1980s, the NRO considered various options to preserve its
capability. I recommend Dwayne Allen Day's excellent article on this:

http://www.thespacereview.com/article/3390/1

The eventual decision was to modify the mission of KH-11 to incorporate that of Hexagon. This was accomplished, at least
in part, by raising its highest altitude to about 1000 km, which afforded a wider view, but with resolution reduced to
28 cm (1 foot) - roughly that of Hexagon. The lowest altitude remained 250 km, which preserved its best resolution of 7
cm (3 inches).

USA 6 was the first KH-11 to employ the higher altitude orbit. Launched in Dec 1984, it was the first of what I call the
Block 2 KH-11. Whether its design was changed to facilitate the wide-area mission is unknown. USA 6 initially operated
in a 700 km apogee orbit, which it raised to 1,000 km during summer and fall 1985. The 250 X 1000 km orbit remains the
primary KH-11 orbit to this day. This information comes from hobbyist satellite observers and orbital analysts, who are
the sole public source of precise orbital elements of these satellites.

4. Future

4.1 Commercial satellites for wide-area surveillance

A quick search of the web reveals that the NGA (National Geospatial Agency) has been purchasing commercial satellite
imagery since at least 2003, and has signed contracts worth many billions of dollars since then.

The U.S. government regulates the resolution of imagery sold by commercial imaging satellite owners. As the best
resolution permitted to be sold improved, so did the satellites. DigitalGlobe claims panchromatic 31 cm resolution from
617 km altitude, for its Worldview 3 and 4 satellites, launched in 2014 and 2016, respectively. This means that
commercial satellites have now achieved approximately the resolution of the Hexagon satellite, that KH-11 replaced by
raising its apogee to 1000 km. This appears to create the opportunity for KH-11 to return to its original, exclusively
high-resolution imaging mission, by returning to the pre-1985 maximum apogee of 500 km. A couple of older KH-11s have
done just that.

4.2 Possible Block 5 clues from KH-11s on extended mission

The typical operational life of the early KH-11 was a few years. The Block 3 KH-11, first launched in 1992, extended the
operational life to about 15 years. Block 4, first launched in 2001, appears to be capable of similar longevity. One
Block 3 and two Block 4 satellites remain in orbit.

Modern KH-11s spend roughly the first half of their life on their primary mission, at which time they are replaced by
fresh satellites. The old spacecraft continue to operate for several years on extended missions, after which they are
de-orbited. At any given time, there are two primary-mission spacecraft, and one or two older extended-mission
spacecraft.

Observations and orbital analysis by hobbyists, revealed that during 2012-2015, both of the spacecraft on extended
missions (USA 161 and USA 186), manoeuvred to lower-altitude orbits, more like those used in the early years of the
KH-11 program in the late 1970s and early 1980s. The extended mission would be ideal for experimentation, which led to
the hypothesis that the return to a lower orbit was a clue of what to expect from the Block 5 KH-11, with NROL-71 the
suspected first launch.

It is known that the primary mirror of Block 5 KH-11 is the same diameter as that of the present generation, 2.4 m.
Amazingly, this was openly announced:

http://spacenews.com/us-intelligence-official-drops-hint-about-next-gen-spy-sat-capability/

Given that the mirror diameter will remain 2.4 m, and the resolution limit imposed by atmospheric turbulence, it is
reasonable to assume that the lowest altitude would be about the same as the present, 250 km. The advantage of the
reduced maximum altitude - no greater than 500 km -  would be more nearly constant resolution during each revolution
about the Earth.

4.3 Block 5 KH-11 NROL candidates

The only publicly known candidates to launch Block 5 KH-11 satellites are the upcoming NROL-71, and NROL-82, scheduled
for 2020. Both are Delta 4-Heavy launches from VAFB. Two of the existing generation of KH-11 were launched by Delta
4-Heavy, but they were designed for the less powerful Titan IV. The payloads of NROL-71 and 82 would be the first that
could have been designed to take full advantage of Delta 4-Heavy, perhaps to carry a greater fuel load, which would
enable them to operate for a longer time in a 250 km by 500 km, or lower orbit, than previous KH-11s.

My confidence that NROL-71 and 82 would launch the first Block 5 KH-11 satellites is based on the following:

A. The following 2009 article reported that Lockheed Martin had begun pre-acquisition work on the next generation
electro-optical satellite, and was expected to receive the contract in 2011 for a "two-satellite system," that would "be
an evolutionary upgrade of the satellites Lockheed Martin has been building for decades." It would have a 2.4 metre
diameter primary mirror - same as that of Block 4:

https://spacenews.com/us-intelligence-official-drops-hint-about-next-gen-spy-sat-capability/

B. First launch dates in 2018 (NROL-71) and 2020 (NROL-82) seem reasonable for a program begun in 2012. As precedent,
consider that Lockheed Martin was awarded the final pair of the Block 4 electro-optical satellites about 2005, and they
were launched in 2011 and 2013.

C. A budget document leaked by Edward Snowden revealed the start of a new program, Evolved Enhanced CRYSTAL System, with
FY12 funding of $1.2 billion, and $1.5 billion in FY13. Assuming (as a guess) average annual spending of $1.3 billion
through FY17, the total cost could be nearly $8 billion, or about $4 billion per satellite.

D. Electro-optical satellites relay imagery to Earth via SDS (satellite data system, aka Quasar satellites).
Historically, the first launches of a new generation of SDS tended to herald a new block of KH-11 satellite.

The first two SDS 2 satellites were launched in 1989 and 1990, and the first Block 3 KH-11 satellite was launched in
1992.

The first two SDS 3 satellites were launched in 2000 and 2001, and the first Block 4 KH-11 satellite was launched in
2001.

The first SDS 4 satellite was launched in 2016 (USA 269 on NROL-61), and the second one in 2017 (USA 279 on NROL-52). We
know they are a new generation because optical and radio tracking by my fellow hobbyists revealed a spin-rate in GTO
(geo-stationary transfer orbit), consistent with Boeing's BSS-702 or 702HP bus. (The 3rd gen SDS employed Boeing's older
HS-601 or 601HP bus, which spun at a different rate in GTO.) The SDS 4 launches in 2016 and 2017 appear to have paved
the way for Block 5 KH-11 launches in 2018 and 2020, consistent with the above pattern.

E. The Block 4-2 spacecraft has been on its primary mission for more than 7.5 years, the third longest after Block 4-1
(9.3 years) and Block 3-3 (8.84 years); therefore, it probably is about due to be replaced.

5. NROL-71 Pre-launch clues

The NOTAMs revealed that the orbit of NROL-71 will indeed be different than that of recent KH-11s. It will enter a 74
deg orbit, instead of the sun-synchronous orbits (SSO) of all previous KH-11s, inclined at approximately 97 deg or 98
deg, depending upon their altitude. I continue to believe that the payload is the first Block 5 KH-11, but it will not
orbit in either of the existing standard KH-11 planes. This radical change may be explained by a desire/need for imagery
taken under more varied illumination conditions than occur with an SSO. Therefore, the NRO and NGA may have decided to
employ an MSSO (Multi Sun-Synchronous Orbit). For my latest ideas and analysis on this and other clues, please see my
post of search elements:

http://satobs.org/seesat/Dec-2018/0045.html

The orbit of NROL-71 almost certainly will be inclined at or near 74 deg. The remaining big question is its orbital
dimensions. Will it be the 250 x 1000 km employed since 1985, or have recent improvements in the resolution of
commercial imagery enabled the return to the 250 x 500 km pre-1985 orbit? Or will it be something entirely different?

Ted Molczan


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