Sunday 22 November 2020

Tracking objects in MEO from the NROL-101 (USA 310) launch [updated]


NROL-101 payload USA 310. Click image to enlarge

On 13 November 2020 at 22:32 UT, the United Launch Alliance (ULA) launched NROL-101 for the National Recconnaissance Office (NRO) from SLC-41 at Cape Canaveral. CSpOC catalogued the payload as USA 310 under #46918 (2020-083A) and also catalogued the Centaur r/b as #46919 (2020-083B). The payload is classified and orbital elements for both the payload and Centaur were withheld, as is usual for NRO launches.

I wrote about this mission in an earlier post. Initially, we thought that this satellite was perhaps a new SDS and would be launched into HEO (a 63-degree inclined 'Molniya orbit'). Subsequent observations of a fuel vent by the Centaur upper stage seen from the western USA four hours after launch did not seem to fit this, and made us speculate whether the payload perhaps was something new and went into a 58 degree inclined MEO (see the discussion at the bottom of this previous post).

The latter speculation turns out to be correct. On November 18, I imaged an object in a 58.5 degree inclined, 11034 x 11067 km Medium Earth Orbit (MEO). It was steady in brightness. The image in top of this post shows the object in a 6-second exposure with a Canon EOS 80D with Samyang 2.0/135 mm lens. 

Observing conditions on this night were very dynamic: at one moment it could be completely clear, then two minutes later completely overcast, and five minutes later completely clear again.

Two night later, on November 20, I imaged a second related object, in a slightly lower 58.8 degree inclined 10510 x 11043 km Medium Earth Orbit.  Below is one of my images:

NROL-101 Centaur RB. Click image to enlarge

This object is slightly variable in brightness, indicating a slow tumble and during it's peaks it is brighter than the first object. The brightness variation has a peak-to-peak period of 140 seconds. Below, the brightness variation can be seen in a 19-image stack:

click to enlarge

A diagram of the measured pixel brightness of the trails in a series of images, shows the mentioned periodicity, and also shows thge presence of a more specular peak at the tops of the curve:

(click diagrams to enlarge)

(note added 24Nov: an update to this curve from video observations, yielding a 138.02 second peak-to-peak period, is here).

For the moment, we interpret the first, steady object in the 58.5 degree inclined orbit as the payload (USA 310), and the second variable object in the 58.8 degree inclined orbit as the Centaur upper stage.

Here is a TLE for the payload, based on a 3.2-day observing arc:

1 46918U 20083A   20326.25970612 0.00000000  00000-0  00000+0 0    08
2 46918  58.5335 293.1790 0007646 263.2891  96.6658  3.77323127    09

RMS 0.01     arc Nov 18.17 UT - Nov 21.37 UT

The orbit repeats in a 3-4-3 days pattern.


Here is a very preliminary TLE for the Centaur RB, based on a short 43-minute observing arc, hence the values for the eccentricity and Mean Motion still are privisional values:

1 46919U 20083B   20325.05807551 0.00000000  00000-0  00000+0 0    07
2 46919  58.8264 292.5498 0070000 327.1858  32.4248  4.01148244    05


[update] Here is an updated elset for the Centaur RB based on a 3-day observational arc:

NROL-101 Centaur
1 46919U 20083B   20327.90329491 0.00000000  00000-0  00000+0 0    05
2 46919  58.8253 291.9447 0155268 103.5440 258.2387  3.86388179    00

RMS 0.02            arc Nov 0.14 UT - Nov 23.00  UT


The preliminary orbits match well with the fuel vent in Northern Saggitarius observed from Joshua Tree, California and Taos, New Mexico, on 14 Nov ~2:30 UT (18:30 local time in Joshus Tree). The positions match to within a few degrees:

click to enlarge [updated figure]

The orbit of USA 310 is decidedly odd. There have never been classified launches in such an orbit before. One commercial object was launched in a somewhat similar orbit (the orbital inclination is lower), the first (and only) of an ill-fated commercial communications network in MEO: ICO F2 (2001-026A) launched in 2001.

Click to enlarge [updated image]


Because this type of orbit is new for an NRO payload, it is probably something experimental, i.e. a technology demonstrator. We can only guess as to the function, although future orbital behaviour might shed some light. Options include: 


- Communications


- SAR imaging

- Low resolution, wide area optical IMINT

- Space-Based tracking.


In seems that the last few years the NRO and associated organisations are experimenting a lot with new, experimental spacecraft and new types of orbit. We have seen a number of launches into ~50-degree LEO orbits for example (e.g. USA 276, and the failed ZUMA launch). Now unusual MEO orbits are added, it seems. It will be interesting to see how this object will behave, and if other payloads will be launched into a similar orbit in the future.

I, for one, welcome these new oddities: when things become too predictable, it gets boring. So yay for the new and unusual! 

ADDED NOTE (24 Nov):
Now that  both the payload and the Centaur r/b have been observed over a reasonable arc and the orbits have improved, I can provide an estimate for the separation of the Centaur and payload: 14 Nov ~1:00 UT, near the southern apex of the orbits. This was followed by an avoidance burn and fuel dump by the Centaur, so there is some leeway in this.

click to enlarge

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