The flashing behaviour of USA 81 (1992-023A)

The video footage above was shot by me on 25 July 2017 and shows the classified satellite USA 81 (1992-023A). It is flashing rapidly, at ~5 flashes per second.

USA 81 is one of two satellites (the other is USA 32; the attempted launch of a third one failed) on which little is known, but that were probably ELINT gathering satellites, probably in the Singleton/SBWASS program. It was launched from Vandenberg AFB on 25 April 1992 with a Titan 23G.

With its earlier sistership USA 32, USA 81 is renowned for the light shows it puts on. It has a very rapid and at times very conspicuous flash cycle of sharp specular flashes, like a disco-ball: the video above shows an impressive example of this. How pronounced the flashing is depends on the viewing angle: the video above catches a brief period, halfway the footage, where it becomes very pronounced.

The flashing is very regular and specular, with a main period of 0.2 seconds and a secondary period half of that, 0.1 seconds.

The diagrams below show this periodicity well. They are the result of an analysis of (part of) the video above with LiMovie and PAST - the analyzed part of the video was the second part, after the camera repositioned, when flashing was most pronounced.

The first diagram shows the observed very specular flashes (blue) and a fitted double sinusoid of 0.2 and 0.2 seconds (red, dashed). They fit very well:

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The two periods are also well discernable in the Lomb periodogram and the fast Fourier analysis below:

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click diagram to enlarge

The earlier sister ship of USA 81, USA 32 (1988-078A), shows the same brightness behaviour (but with a main periodocity of 1.2 seconds) with the same periodicity. This points out that the flashing is intentional.

There are two options to explain the flashing behaviour. One is that the satellite is spin-stabilized. The other is that the satellite could have a large and shiny rotating element, for example a large rotating antenna.

The Lacrosse 5 "disappearance trick" captured on video

Note: the video below was featured (with my permission) on Spaceweather.com. Unfortunately, it was initially suggested there (and this definitely did not come from me) that the discussed "disappearance trick" is a deliberate "stealth" feature of this satellite.

It almost certainly is not: it is something brough about by accident from something specific in the satellite design.

I also want to make clear, as it kept popping up in the YouTube comments (which I have now disabled), that this is not the moment the satellite disappears in earth shadow! The drop in magnitude happened at 17:35:20 UTC: shadow entry was much later, 17:38:55 UTC.

The video above was shot by me Friday evening (11 Nov). It shows Lacrosse 5 (2005-016A), the latest of the Lacrosse SAR satellites.  It was launched in 2005. In the movie, it is doing it's infamous "disappearance trick" (also note the old Russian rocket stage visible in the second part of the footage).

The brightness behaviour of this satellite is different from that of the previous Lacrosse satellites. Apart from that it is brighter overall and a bit yellowish in colour (the others are distinctly orange-reddish), it shows a variable brightness behaviour that the other Lacrosse satellites do not show (or at least not to this extreme extend).

Lacrosse 5 can sometimes drop several magnitudes in brightness, typically from +1 (easy naked eye) to +5 or +6 (naked eye invisibility or near-invisibility), in a matter of seconds.

After observing this a couple of times, I coined it the "disappearance trick", a term that has stuck in the amateur satellite observer's community.

While many satellites can flare briefly (and the Lacrosses do), this opposite effect of one suddenly dropping in brightness other than due to normal phase angle changes or entry into earth shadow (which is not the case here!!!), is not quite common. And Lacrosse 5 does it that frequently, that it stands out.

Normally, when a satellite or spent rocket stage shows sudden changes in brightness, it is due to either:

a) the satellite entering earth shadow;
b) the satellite is tumbling.

Both are not the case here. These "disappearance tricks" of Lacrosse 5 happen well before the point of shadow entry. In addition, the behaviour is not the typical "flashing" behaviour of a tumbling or spinning satellite. There is no periodicity, and the drop in brightness happens after a long period of stable brightness.

The behaviour is interesting, because the sister ships of Lacrosse 5 (the other Lacrosses) do not typically show this behaviour. The implication is, that Lacrosse 5 is different in design than Lacrosses 1 to 4.

I have photographically documented the phenomena several times, including brightness curves (see here, and a comparison of several curves showing the phenomena here, featuring the comparative diagram shown below).

click diagram to enlarge

Philip Masding has been documenting the phenomena as well, his results can be seen here. His curves also show, and I have seen this happen as well, that Lacrosse 5 can sometimes "re-appear" (and, as I have seen occasionally, next "disappear" again...).

One point is, that we so far cannot find a clear pattern in this all. The satellite does not seem to do this at specific phase angles for example.

We are still at a loss to explain this behaviour. Please note: we don't think it is an intentional "stealth" characteristic. Yet it must have something to do with the satellite design or operation.

Is it a matter of strongly differing reflectance properties of the satellite body with illumination angle? Is it some brightly reflecting appendage on the satellite disappearing from view? Is it a dark appendage on the satellite starting to block view of the illuminated satellite body, or casting a shadow on it? Is it due to some moving part of the satellite, e.g. a moving dish antenna?

We simply do not know. And it is giving us a nice puzzle.

The photograph below, taken in addition to the video footage above, shows Lacrosse 5 in the bright phase of Friday's trajectory.

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Apart from Lacrosse 5, I observed a couple of other satellites last Friday, including the NOSS 3-5 duo (11-014A & B) and USA 32 (88-078A)

The brightness behaviour of USA 32 on 26 June

On 26 June I captured the 22-year-old ELINT USA 32 (88-078A). It displayed a regular brightness variation while passing through the zenith:

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Below is the resulting brightness profile, and a diagram showing the delta T (in seconds) between brightness peaks. The period between the major peaks is regular and near 1.20 seconds. This is similar to what I determined for this satellite in January 2009 (see my post here). There is a hint of 2 lesser peaks present between each main peak.

click diagrams to enlarge

Progress-M 04M, MSX, and Mentor 2

A long spell of very warm, sunny weather is resulting in several clear nights. Since my last observations reported here (those of June 2nd), I have been able to observe on June 3, 13, 14, 16, 17, 22, 24, 26 and 29. Objects include Progress-M 04M, Mentor 2, Mentor 4 (USA 202), USA 161, USA 32, USA 184, MSX, Milstar 5, the NOSS 3-1 duo, and the STSS Demo-1. This does not include a number of non-classified strays also captured.

USA 161 (01-044A) slowly flared to -1 at 23:58:59 UTC (24 Jun).

Below are a few pictures. First: UARS captured as a stray, flaring, on June 16th:

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Progress-M 04M on 26 and 29 June:

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Geostationary USA 202 (Mentor 4), in the trees low in the sky (altitude about 17.5 degrees):

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Mentor 2 (geostationary), MSX and a stray (HJ-1A, a Chinese Earth Observation Satellite)

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NOSS 3-4 duo through Perseus

An initially very clear evening today allowed observations again. Lacrosse 3 (97-064A) was captured, along with NOSS 2-3D (96-029D) and the NOSS 3-4 duo (07-027A & C). USA 32 (88-078A) was captured as a very faint trail but not measured.

A mistake of one minute in the timing while trying to photograph the 96-029 objects made me miss the C & E objects, but captured the D object at the end of what seems to be a slow flare.

One of the images of the NOSS 3-4 duo, the one where they cross Perseus just below the alpha Persei star association, turned out particularly nice, with lots of stars and two bright trails:

(click image to enlarge)

The glinting behaviour of USA 32 (88-078A)

The year 2009 has started with a period of frost, and hence clear skies. I observed on January 6 and 9 and this evening (the 11th), catching a batch of objects: Lacrosse 3, USA 32, and various NOSS duo's.

The image of USA 32 (88-078A, a SIGINT satellite launched in September 1988) of this evening very nicely shows the glinting behaviour of this satellite. Along the trail, small bright dots (= very short glints) can be seen at regular intervals. They are indicated by the downward pointing arrows in the image (a 10.05 second exposure taken with my Canon EOS 450D and EF 50/2.5 Macro lens at F2.8):

(click image to enlarge)

Below is a brightness profile derived from the pixel brightness along the trail. The same peaks as indicated by the arrows in the photograph, show up well and are labelled A to H:

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Analyzing the position of the glints, shows the following sequence:

1) a series of 4 or more glints at a regular 1.20 second interval;
2) followed by 2.0 seconds of no, or much less bright glints;
3) followed again by 4 or more glints at a regular 1.20 second interval.

ISS and the Moon

Another clear evening yesterday. The moon is now becoming more and more prominent in the sky. The International Space Station (ISS) made a pass that brought it close to it in twilight at 18:44 local time (17:44 UTC). I made the photograph below with my Canon Ixus on maximum zoom and 2s exposure:

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I also made another moon shot through my ETX-70 telescope:

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Later that evening, telescopic points were obtained on the ELINT sat USA 32 and Keyhole sat USA 129.

Twice the ISS, and a bag of other objects

Yesterday I observed the International Space Station (ISS) twice. The first observation was in deep twilight, 20 minutes after sunset with the sun at only 4 degrees below the horizon.

I filmed this pass, using the "movie"-mode of my Canon Digital Ixus photo camera. The resulting short movie is below: it shows the ISS descending towards the east.



Later that evening, one pass later, I shot this photograph, which shows the ISS crossing Taurus just before entering earth shadow:

(click image to enlarge)

Both this evening and the morning of today (the 11th) I telescopically observed a number of other objects; the keyhole USA 129 (96-072A), the ELINT USA 32 (88-078A), the SAR satellites Lacrosse 5 (05-016A) and Lacrosse 3 (97-064A), and the NOSS 3-2 duo (03-054A & C) and, as a stray while waiting for USA 32, the old NOSS 6F (84-012F).

In addition, I shot this photograph of the crescent moon through my Meade ETX-70 in the late afternoon/early evening:

(click image to enlarge)

Observing ISS and two of its Progress cargo spacecraft

Yesterday evening was very clear, and provided the rather unique opportunity to see the International Space Station (ISS) pass in twilight, followed several minutes later by two of its cargo Spacecraft: Progress-M62 (07-064A) decoupled from ISS on Wednesday and now moving away from it carrying garbage, and Progress-M63 (08-004A) launched from Baikonur in Kazachstan on Wednesday and on its way to the ISS with fresh cargo. Seeing two Progress spacecraft in free flight on the same evening is unique.

ISS was the first to pass, still in deep twilight, at 18:15 local time, being around mag. -3. Five minutes later Progress-M62 followed on a trajectory a few degrees higher, grazing the Hyades cluster, and being about mag. +1. And twelve minutes after that, the newly launched Progress-M63 followed in a very similar trajectory. By that time, although the sky was still bright due to twilight, it was dark enough to try to photograph it. The resulting photograph has a very bright background drowning the trail, but after some image manipulation for brightness and contrast it is visible:

(click image to enlarge)

I logged a point for Progress-M63 through the telescope, and the endpoint of the trail on the image above provided a second point.

Later in the evening I observed Lacrosse 2 (91-017A), which by now was 34.6 seconds early, the USA 32 ELINT sat (88-078A), Lacrosse 5 (05-016A) and the NOSS 3-2 duo (03-054A & C), the latter duo on two consecutive passes.

Like previous days it was again clouded in the morning, so no chance to observe USA 193.

Tomorrow evening is going to prove very interesting, I hope. The weather prospects are good, and if the launch isn't postponed this evening, I will have a very good 80 degree post-twilight pass of Space Shuttle Atlantis STS-122. In addition, the ISS and the two Progresses can be observed again. Plus, the Soyuz rocket booster (08-004B) from the Progress-M63 launch could prove very interesting, as it will make two passes (one visible and one in shadow) while close to decay.

Lacrosse 2 manoeuvred again (updated)

Yesterday evening was very clear. While looking up some deep-sky objects and while waiting for target satellites to appear, I saw several faint strays.

Lacrosse 2 (91-017A) was 21.6s early and 0.16 degree off-track relative to a week old elset 08027.82795435. Hence, just like early January, it appears to have manoeuvred again.

Update: Russell Eberst's data of the same pass confirm my observation. From a very preliminary analysis I did, it seems that the manoeuvre entails a similar mean motion change by about +0.0005 as was the case early last month.

Other objects observed this evening were the ELINT sat USA 32 (88-078A) and the NOSS 3-2 duo (03-054A & C). In addition, I observed the International Space Station making a pass through Taurus just beneath the Hyades and Pleiades. I had not realised the decoupled Progress M-62 would be following it closely, so I missed that one (it also was just too far behind ISS to show up on the photograph I shot, see below).

(click image to enlarge)

It was overcast this morning so again no chance to observe USA 193. It is still overcast, so I am going to miss both the old and new Progress (the latter launched today) tonight. I hope it clears in time to observe them and the Space Shuttle STS-122 that is scheduled to launch next Thursday.

Of NOSS-es, strays and neighbours

Yesterday the 22nd of January started clear and ended clear, albeit with a near full moon. I did an observing session with the ETX-70 telescope in morning twilight as well as in the evening.

The result: positions on the NOSS 3-4 pair (07-027A & C), the NOSS 3-3 pair (05-004A & C) and the NOSS 3-2 pair (03-054A & C), plus stray observations of the ELINT sat USA 32 (88-078A) and the spent Russian rocket Kosmos 1171r (80-026B). I also observed the NOSS 2-2 C & D pair, but couldn't log points (There was only a short time to re-aim the telescope between this pass and the NOSS 3-3 pass, and it then took me just too long to verify I had the correct star field. I saw them pass the FOV but couldn't get to clock them in time.).

During the morning session I unintendedly startled one of my neighbours when she came out of her house and saw me on the courtyard with my telescope. She went into a panicky fit as a result. This was just as I was about to catch 07-027A. The resulting melée and the added unexpected appearance of 88-078A as a "stray" only 11 seconds before 07-027A make me suggest to use the 07-027A point with some caution (by the time of 07-027C I should have regained my composure).

Some time after the end of the evening session, I portrayed the nearly full Moon. Below image is a quick shot made by simply pressing the (non-removable) objective lens of my Canon Ixus compact on the eyepiece of my ETX-70 telescope. Some after-editing has been done to the image to bring out detail.

(click image to enlarge)