Monday 17 December 2018

NROL-71: an enigmatic launch [UPDATED]

(this post on NROL-71 is belated, as I was in hospital around the original launch date. Luckily, launch got postponed)

click map to enlarge

If nothing ontowards happens, the National Reconnaissance Office (NRO) will launch NROL-71, a Delta IV-Heavy with a classified payload, from Vandenberg SLC-6 on 19 December 2018 (18 December local time). [edit:] after the December 19 launch was scrubbed, a new launch attempt will take place on December 20 (December 19 local time in the USA). The December 20 launch was scrubbed as well due to a hydrogen leak in one of the boosters. A provisional new launch date is 21 December 2018 (December 20 local time in the USA) at 1:31 UT.

The new launch date will not be before 30 December 2018.

The launch was postponed three times. Originally to be launched on December 8, a communications problem aborted that launch. A renewed launch attempt the next day, was aborted only 7.5 seconds before lift-off because of a technical issue (see the video below).

A new launch attempt will take place on 19 December 2018 at 1:57 UT. As weather prospects at the moment do not look particularly good for that date, it is possible that the launch will see even further postponement. [edit:] This assessment turned out to be right: the launch was postponed due to high altitude winds. A new launch date has been set for 20 December 2018 at 1:44 UT. The December 20 launch was also aborted, due to a hydrogen leak in one of the boosters. A provisional new launch date has been set for 21 December (20 December local time in the USA) at 1:31 UT. The new launch date will not be before 30 December 2018.

NROL-71 is an odd launch. When the Maritime Broadcast Warnings for the launch came out and revealed the launch hazard areas, they contained a big surprise. The general expectation among analysts was that NROL-71 was the first of the Block V new generation KH-11 ADVANCED CRYSTAL electro-optical reconnaissance satellites. As such we expected it to go in a sun-synchronous, 97.9 degree inclined, 265 x 1000 km orbit.

But the Maritime Broadcast Warnings suggest this is NOT the case. The hazard areas are incompatible with such a sun-synchronous polar orbit. Instead, they point to a (non-sunsynchronous!) 74-75 degree inclined orbit. Not what you expect for an optical reconnaissance satellite!

The map below shows the three hazard zones. Two are directly downrange from the launch site, where the strap-on boosters and first stage splash down. The third area is the upper stage deorbit area (which is remarkably small in size), located northeast of Hawaii, with deorbit occuring near the end of the first revolution (as usual).

click map to enlarge

The trajectory depicted by the dashed line on the map is for a 74-degree inclined, 265 x 455 km orbit. Higher inclined orbits would miss the downrange splashdown zones and the upper stage deorbit area.

Ted Molczan has pointed out that the shift in launch time with each launch delay, points to a specific orbital plane and a specific aim for the rate of precession of the RAAN of -2.27 deg/day.

This is over twice as fast as the RAAN precession of the KH-11 currently in orbit (0.98 deg/day, i.e. sun-synchronous).

This value for the RAAN precession apparently aimed for, puts further constraints on the orbit as in combination with the 74-degree inclination deduced from the location of the Launch Hazard areas it points to a semi-major axis of about 6735 km.

Going from the notion of KH-11-like orbital altitudes, the current typical KH-11 perigee near 265 km would then result in an apogee near 455 km. This is somewhat similar to the orbital altitude of the oldest of the KH-11 on orbit, USA 186 in the secondary West plane, which was in a 262 x 443 km orbit when we last observed it early October (it currently is invisible due to the winter blackout). This apogee would be much lower than that of the two KH-11 payloads in the primary planes, which have apogee near 1000 km, i.e. twice as high, another deviation from expectations. Normally, KH-11 are launched into a primary plane and about 265 x 1000 km orbit, and only after some years, when the payload is moved to a secondary plane (and a new payload is launched into the primary plane), is apogee lowered to ~450 km (see an earlier post here).

So, if NROL-71 is a new electro-optical reconnaissance satellite in the KH-11 series, it represents a serious deviation from past KH-11 missions. The apparent abandoning of a sun-synchronous polar orbit, is surprising, as such orbits are almost synonymous with Earth Reconnaissance. The "why" of a 74-degree orbit is mystifying too. If it does go into a 74-degree inclined orbit, it doesn't seem to be a "Multi-Sun-Synchonous-Orbit".

Alternatives have been proposed. Ted Molczan has for example suggested that, perhaps, NROL-71 could be a reincarnation of the Misty stealth satellites, warning that the unexpected orbital inclination for NROL-71 might not be the only surprise.

I myself was struck by the fact that 74-degree orbital inclination is the prograde complementary of the retrograde 106 degree inclination of the FIA Radar/TOPAZ 6 payload (USA 281,  2018-005A) launched early this year: note that 180-106 = 74. FIA Radar 6 was the first in a new block of TOPAZ radar payloads, just like NROL-71 appears to be the first in a new block of  'something'.

The previous four FIA Radars, launched into 123-degree inclined orbits, were the retrograde complementary in inclination of the prograde 57-degree Lacrosse 5 orbit, another radar satellite. The complementary character of 106-degree versus 74-degree for NROL-71, could perhaps point to NROL-71 being a Lacrosse Follow-On, as a complementary to the newest FIA block.

If NROL-71 is a Lacrosse Follow-On, its orbital altitude and brightness behavious might yield clues: Lacrosse 5 has shown a very distinct brightness behaviour.

It will be very interesting to chase this launch. If launch occurs on 19 December near 1:57 UT and weather cooperates, Europe will have visible evening twilight passes in the first few days.

Below are a couple of search orbits. All are for an assumed 74-degree orbital inclination and launch on 19 December at 1:57 UT. The first three are for KH-11 like orbital altitudes. The fourth is for a Lacrosse-like orbital altitude.

Orbit #70003 fits the hazard areas from the Maritime Broadcast Warnings best.

[EDIT: new updated search orbits below, for the new launch date, 19 Dec 20918 1:44 UT

[EDIT: new updated search orbits below, for the new launch date, 21 Dec 2018 1:31 UT]

NROL-71                                                 265 x 1000 km
1 70001U 18999A   18355.06319444  .00000000  00000-0  00000-0 0    00
2 70001 074.0000 184.7636 0524203 155.2439 326.4145 14.78994708    03

NROL-71                                                  265 x 500 km
1 70002U 18999A   18355.06319444  .00000000  00000-0  00000-0 0    01
2 70002 074.0000 184.7636 0173800 155.2439 324.5345 15.61785606    06

NROL-71                                                  265 x 455 km
1 70003U 18999A   18355.06319444  .00000000  00000-0  00000-0 0    02
2 70003 074.0000 184.7636 0140989 155.2439 324.3567 15.69614809    07

NROL-71                                                  715 x 725 km
1 70004U 18999A   18355.06319444  .00000000  00000-0  00000-0 0    03
2 70004 074.0000 184.8196 0007044 155.2265 327.0336 14.51731413    06

Note that deviations of many minutes in pass time and several degrees deviation in cross-track are possible on all four orbits, certainly several revolutions after launch.