Thursday 23 March 2017

NOSS 3-8 (NROL-79) components now close to operational separation

In a recent blog post I documented the intricate manoeuvering of the two NROL-79 payloads (NOSS 3-8) over the past three weeks. They were manoeuvering to circularize and synchronize their orbits and manoeuvre to a desired mutual distance.

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Much of this manoeuvering is now done, and the two spacecraft are now flying in formation at a mutual distance of ~50.5 km. They now look like a typical NOSS pair, as can be seen in the image above shot in the evening of March 21 (the bright star is Procyon).

Below is an updated diagram, showing the evolution of the separation between the two spacraft over time:

click diagram to enlarge

After an initial rapid post-launch separation with a drift of ~31-32 km/day, reaching a maximum separation of ~202 km on day 6 after launch, the separation distance started to decrease post day 6, and is now, by day 20-21 after launch, clearly flattening out to a stable separation distance of about 50 km.

The Mean Motion/orbital period of the two spacecraft are now very similar too, as is their orbital inclination: all signs that they are now close to the desired configuration. The two orbital planes are currently about 0.2 degree separated in RAAN.

click diagram to enlarge
click diagram to enlarge
click diagram to enlarge

While they are now at their operational distance (which looks to be ~50 km in this case) and close to operational configuration, this does not mean that NOSS 3-8 is now fully operational. Over the coming weeks, they will probably undergo extensive check-out tests. I also expect them to continue to make small manoeuvres for a while (but while maintaining a more or less stable mutual distance at ~50 km).

Several amateur satellite trackers contributed data to this analysis, including Leo Barhorst, Cees Bassa, Russell Eberst, Alain Figer, Paul Camilleri, Dave Waterman, Alberto Rango, Brad Young and me.

Sunday 19 March 2017

NOSS 3-8 (NROL-79): Dancing in the Dark

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The image above shows the new NOSS 3-8 duo (2017-011 A & B, launched as NROL-79 on March 1, see my earlier blog post here), aka USA 274, imaged on March 12 through very thin cirrus.

Over the past 2.5 weeks a number of us (Leo Barhorst, Cees Bassa and me in the Netherlands; Russell Eberst in Scotland; Alain Figer in France; and Paul Camilleri in Australia) have been chasing this duo and monitored their manoeuvering, consisting of small adjustments in apogee and perigee and orbital period.

Click diagram to enlarge

I expect their manoeuvering to be complete by 21 days (3 weeks) after launch, i.e. near March 23. They will then have attained their finalized separation distance. I expect this initial operational distance to be about 45 km. I do not exclude further small manoeuvres after March 23 though, but these will be more as a pair, and not with respect to each other.

NROL-79 consists of a NOSS (Naval Ocean Surveillance System) duo: two payloads orbiting as a close pair (typically 30-55 km). The second object is  catalogued as "debris" by JSpOC (they did this with all second payloads of NOSS launches), but isn't: after all, real debris shouldn't manoeuvre, and shouldn't stationkeep with respect to the other payload.

click diagram to enlarge

After insertion in a 1010 x 1204 km, 63.45 degree inclined orbit, the two payloads started an intricate dance in space, step by step positioning themselves with respect to each other.

In the initial week after launch the two payloads separated at a rate of ~31-32 kilometer per day, to a maximum separation of just over 200 km on Day 7. Then their drift reversed, with the two payloads gradually moving closer again (see diagram above, which also gives similar data for a previous NOSS launch, NROL-55 (NOSS 3-7) from 2015). Extrapolating the drift, and looking at the previous NOSS launch, I expect that by the end of the 3rd week after lauch (~March 23, 2017) the two payloads will reach their intended separation of ~45 km, and stabilize with respect to each other.

It is interesting to note the difference with the previous NOSS launch, NOSS 3-7, also depicted in the diagram. The latter initially drifted further apart, and for a longer time: the separation increased until 14 days after launch (double as long as for the current case), to as much as ~570 km (almost three times as large as the current case), before the two objects started to move closer again.

In the image below, taken three days apart on March 10 and March 13, the decrease in distance over time after the first week can clearly be noted (in the images, movement is from top to bottom and the B-object is leading). The images show the payloads in roughly the same part of the sky (bright stars are 1, 10 and 13 Cyg):

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A first major manoeuvre occurred on day 6, when both payloads lowered their orbital period:

click diagram to enlarge

Around that same date, the visual brightness of the two objects changed. The latter probably signifies the deployment of something on the payloads: either antennae, or perhaps panels used to make minor orbital adjustments by decreasing or increasing drag (it has long been rumoured that this is one of the ways the NOSS payloads maintain their bond).

The pattern between the current launch and the previous launch is similar (although I have a suspicion that for the previous NROL-55 launch in 2015, analysts switched the identitities of the two objects around day 6): a major orbital period adjustment on day 6, after which one of the payloads gradually increases its orbital period again while the other very slowly decreases its orbital period. But what can be seen is that for the current case, the values for both payloads stay much more similar than was the case with the previous launch, just as with the evolution of the spatial separation of the two. One of the things this could point to is that, perhaps, the initial orbit insertion of NROL-79 went better than for NROL-55, but this is speculation.

Note: orbital calculations for NROL-79 used were done by myself using observational data from the persons mentioned in the main text. The NROL-55 orbit calculations from 2015 were by Mike McCants and  Ted Molczan. I am indebted to Leo Barhorst and Bram Dorreman for their help in filling gaps in my archive of orbits for the latter object.

Thursday 16 March 2017

USA 186 recovered

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The image above shows USA 186 (2005-042A), a KH-11 ADVANCED CRYSTAL ("Keyhole") optical reconnaissance satellite. It is cruising just below the Pleiades star cluster in this image, which I shot yesterday evening using the Samyang 1.4/85 mm lens and an exposure of 2 seconds.

USA 186 was recovered last week after being briefly lost in the Northern hemisphere winter blackout. Leo Barhorst made one or two possible detection in February, but it was Cees Bassa who unambiguously recovered it on March 13th. Two days later, I made the image above.

The arc is still short, but it appears to be in an approximately 265 x 435 km sun-synchronous orbit. The apogee is some 20 km lower than it previously was, the perigee is about 5 km higher (i.e., the current orbit is more circular than previous orbits). It's ground repeat interval is 4 days.

USA 186 is the secondary West plane satellite in the KH-11 constellation. The hunt is now on for USA 245, the primary West plane KH-11. Recovery of the primary East plane KH-11, USA 224, will have to wait untill early summer.

When I observed it yesterday it was bright (mag +1.5) and briefly flared to mag 0 near 19:32:50 UT (March 15, 2017).

Friday 3 March 2017

Tracking NROL-79, a new NOSS duo

Launch of NROL-79 from Vandenberg on March 1, 17:49 UT (photo ULA)

On March 1, 2017, at 17:50 UT,  an Atlas V rocket was launched from Vandenberg with a classified (double) payload for the National Reconnaissance Office (NRO) onboard. It was the 70th Atlas V mission, and the 14th NRO launch using this launch vehicle.

The two payloads were launched towards a southern direction into a 63.46 degree inclined, 1010 x 1204 km orbit. The payloads are almost certainly a new set of NOSS (Naval Ocean Surveillance System) satellites, NOSS 3-8 (NOSS satellites are also known under the code name INTRUDER). These are SIGINT/ELINT satellites operating in close, formation flying pairs. The purpose of these satellites is to geolocate radio signals, notably signals originating from ships. In order to keep their mutual distance  stable, they operate in 63.4 degree orbits, a critical inclination which keeps perigee in a stable position.

This is the 8th launch in the third generation of these spacecraft.

Based on estimated search elements, both payloads were quickly picked up by amateur trackers. Russell Eberst in Scotland and Alain Figer in France first spotted them about 10 hours after the launch, on March 2.  Paul Camilleri in Australia soon followed. I was clouded out that night, but the next night (March 3) was clear in Leiden, and I managed to image the payloads on two consecutive passes, albeit under a somewhat hazy sky. It was also imaged by Leo Barhorst that same night.

Below are two of my images of the two payloads chasing each other, from consecutive passes, obtained from Leiden under a hazy sky (click them to enlarge):

NROL-79 payloads, image 3 March 2017, 1:43 UT (click to enlarge)

In the image above taken during the first pass near 1:43 UT, the objects are moving from top to bottom through a field in Cygnus. In the image below, from the second pass, they are moving from left to right. Note the difference in brightness between the two objects, noticable during this second pass:

NROL-79 payloads, image 3 March 2017, 3:31 UT (click to enlarge)

The NOSS components are usually designated A and B (sometimes A & C). For the moment, we have named the fainter leading object B. The objects are currently still quite faint, indicating that they have not yet deployed their solar arrays and other gear.

The B object is usually catalogued as "debris" by JSpOC, but this is a ruse: in reality it is a functional payload (as it manoeuvres and carefully stationkeeps with the A component during its operational years).

Our current tracking data established that they are in a 63.46 degree inclined, 1010 x 1204 km orbit. The two payloads are about 45 km apart in space.

Over the coming days, they will likely make manoeuvres to finalize their orbits and respective positions.

The respective distances of current still operational NOSS pairs (NOSS 3-3 to 3-7) varies between 39.5 and 55 km.