NROL-108: another mystery launch perhaps similar to NROL-76 (USA 276)? [UPDATED]

UPDATE 17 December 2020 16:15 UT:

today's launch was scrubbed due to a pressure anomaly in the upper stage. A new launch attempt will be on December 18th 19th.

UPDATE 20 December 2020 12:20 UT:
NROL-108 launched succesfully on 19 december at 14:00 UT. A fuel dump was observed from New Zealand.

On 17 18 19 December 2020, SpaceX will launch a classified payload for the National Reconnaissance Office (NRO). The launch, from Cape Canaveral platform 39A in Florida, is designated NROL-108. The Navigational Warnings window opens at 13:55 UT and closes at 17:52 UT, pointing to launch somewhere between ~14:00-17:45 UT [edit: the scrub on December 17 suggests a window starting at 14:45 UT and ending at 17:00 UT] . The first stage will attempt to do a RTLS (return-to-launch-site).

NROL-108 is very odd as it was a surprise addition to the launch schedule in early October 2020, seemingly coming out of nowhere. It was originally slated for launch on October 25, but was postponed to December. The character of the mission is a mystery: this looks to be something new again.

The following Navigational Warnings have appeared for the launch hazard areas and the Falcon 9 upper stage deorbit area:

 NAVAREA IV 1201/20
 WESTERN NORTH ATLANTIC.
 FLORIDA.
 1. HAZARDOUS OPERATIONS, ROCKET LAUNCHING
    171355Z TO 171752Z DEC, ALTERNATE
    181355Z TO 181752Z DEC
 IN AREAS BOUND BY:
 A. 28-39-43N 080-38-12W, 29-02-00N 080-15-00W,
    28-57-00N 080-08-00W, 28-40-00N 080-11-00W,
    28-27-00N 080-24-00W, 28-26-52N 080-32-07W.
 B. 30-12-00N 079-06-00W, 30-28-00N 078-56-00W,
    30-54-00N 078-52-00W, 31-14-00N 078-13-00W,
    31-06-00N 077-36-00W, 30-47-00N 077-22-00W,
    30-27-00N 077-26-00W, 30-08-00N 078-20-00W,
    30-03-00N 078-58-00W.
 2. CANCEL THIS MSG 181852Z DEC 20.//

 HYDROPAC 3673/20
 EASTERN PACIFIC.
 DNC 06, DNC 13.
 1. HAZARDOUS OPERATIONS, SPACE DEBRIS
    171508Z TO 171841Z DEC, ALTERNATE
    181508Z TO 181841Z DEC
 IN AREA BOUND BY
    12-27S 135-24W, 11-03S 135-01W,
    04-31N 125-02W, 12-23N 118-23W,
    11-34N 117-22W, 01-11N 123-20W,
    11-32S 132-38W, 13-10S 134-27W.
 2. CANCEL THIS MSG 181941Z DEC 20.//

These hazard areas plotted on a map:

click map to enlarge

 

The time window for the upper stage deorbit and the fact that the first stage will attempt an RTLS point to a launch into Low Earth Orbit. The launch direction and the location of the Falcon 9 upper stage deorbit area point to a launch into an orbit with an orbital inclination near 52 degrees.

The location of the launch hazard areas is somewhat similar to the launch hazard area for the May 2017 mystery launch of USA 276 (NROL-76). In the map below, the two hazard areas for NROL-108 are in red, while the launch hazard area for NROL-76 (USA 276) from May 2017 is in blue:

click map to enlarge

USA 276/NROL-76 was a mystery NRO launch, like NROL-108 launched by SpaceX, in May 2017, that raised eyebrows because the payload made a series of very close flyby's of the International Space Station a month after launch (see my July 2017 article in The Space Review).

USA 276 went, as subsequent orbital observations of the payload by our amateur network showed, into a ~400 km altitude, 50-degree inclined orbit, so a 50-degree inclined orbit is perhaps also an option for NROL-108.

Such a 50-degrees inclined orbit does not match well with the position of the deorbit zone for the Falcon 9 upper stage. The latter will be deorbitted over the eastern Pacific near the end of the first revolution, the Navigational Warnings show. So for now, the 52-degree inclination (give or take a degree) looks a bit more likely. Still, I do not want to rule out a 50-degree inclined orbit altogether, as the Falcon 9 upper stage might end up in a somewhat different orbit than the payload

In May 2017, USA 276 was launched into an orbital plane very close to that of the ISS, which resulted in the close encounters a month later. 

The launch window for NROL-108 (~14:00-17:50 UT) rules out that NROL-108 will do something similar: the ISS orbital plane does not pass over or near the launch site during this time window. 

It is possible however that NROL-108 aims for an orbital plane near that of USA 276. The orbital plane of USA 276, which due to orbital precession over the past 3 years no longer is close to that of the ISS, passes over Cape Canaveral Launch Pad 39A near 17:02 UT, inside the NROL-108 launch window. This opens up the possibility that NROL-108 is perhaps a close approach target for USA 276, or USA 276 is a close approach target for NROL-108 (but that is pure and wild speculation: Caveat Emptor). [UPDATE: see the update at end of this post. It did not target the USA 276 orbital plane]

It will be interesting to see in which orbit NROL-108 will end up. As I have remarked with some launches earlier  this year, the latest NRO launches all seem to be  'new' kinds of payloads that are likely experimental/Mission demonstrators, and which go into 'new' kinds of orbits: lately we have frequently seen orbital inclinations near 50-degrees and odd orbital altitudes (either very low or very high). NROL-108 will certainly go into a Low Earth Orbit, and it will be interesting to see what the exact launch time will be, whether it will go into a 400 km orbit similar to the orbital altitude of USA 276, and what the eventual orbital inclination will be.

UPDATE 20 December 2020:

NROL-108 launched succesfully at 14:00 UT on December 19th. Slightly over an hour after launch, near 15:15 UT, a fuel dump (following a deorbit burn) from the Falcon 9 upper stage was observed from New Zealand. The facebook-post here shows the classic spiral shape of such a fuel dump. The Youtube video below shot from Pukehina Beach by Astrofarmer shows less detail but includes time details:

 

 

Assuming the included times in the video are correct, this allows me to make a new estimate of the orbital altitude in which the satellite was inserted, which is probably ~600 km rather than the ~400 km of my initial estimate, looking at the time the rocket stage passed south of New Zealand:

NROL-108
1 70000U 20999A   20354.58333333  .00000000  00000-0  00000-0 0    04
2 70000 051.9000 194.4979 0003581 047.9699 326.1978 14.88539141    08

The orbital inclination of the satellite is still a bit uncertain but likely ~52 degrees.

The launch time (14:00 UT) excludes that the orbital plane of USA 276 was targetted (the orbital plane of the latter passed over the launch site two hours after launch).

 

UPDATE 2 (20 Dec 2020):

Radio observers have now catalogued the payload in a 519 x 539 km, 51.35 degree inclined orbit.