Most accelerations happen with Cosmos rockets from two groups:
1:inclination 73.9 to 74.0, apogee +- 770 km, perigee +- 805 km examples: 87- 49 B, 88- 53 B, 87- 98 B, ...
2:inclination 82.9 to 83.0, apogee +- 950 km, perigee +- 1000 km examples: 89- 28 B, 89- 59 B, ...
But last month another interesting object had accelerated:
87- 60 A = 18187 93-06-29 LB almost S, mag 5 93-10-17 TC S, mag +2.5, u 94-05-11 TC S, mag +6.5 96-05-15 KJ 8.0 96-05-15 TC 8.30 AA, mag +3On May 16 Tristan announced on SeeSat-L:
Last night(May 15) I found Kosmos 1867/18187/87-60A to be flashing with 8.30s Kosmos 1867 is the second Eorsat(after 87-11A) which has been launched in this orbit and which is flashing now. I suppose it is venting some fuel right now and therefore it could be accelerating just as 87-11A has done a while ago.
I then checked the evolution of the mean motion, see below.
On the Semi Major Axis graph you can see that there were TWO jumps in Mean Motion during the last years: The first one happened between 94 Aug 18 and 22. Semi major axis decreased suddenly from 7169.726 to 7169.623 km, a jump of 100 metres. The second one is the one Tristan mentioned. It occured between 95 Dec 21 and 96 Jan 3. An decrease of 40 metres.
Comparing these jumps with those happening with rockets the difference is that for a rocket it can take several days or weeks for the elements to become stable again. For this payload there is a very sudden jump; before and afterwards the semi major axis is very stable (slowly decreasing linearly).
As you can see from the PPAS-extract we have no observations in our Database to conclude what jump caused it to accelerate and how it accelerated. It would be very interesting to compare the acceleration of a payload to a rocket! So keep on observing!
1 18187U 87060 A 96137.11789093 .00000007 00000-0 27536-5 0 4103 2 18187 65.0080 170.2565 0016062 278.7097 81.2167 14.30107991462144
Stephen Thompson later acknowledged on SeeSat-L:
Last Christmas Eve ( 95358 or early 95359 UT) I was out satellite watching and caught Cosmos 1867. My notes only show it as 'faint to the naked eye' that usually implies about mag 5 where I live. I made no note of any variation in brightness.
Tristan gave some more information about this payload:
Kosmos 1867 is the second and until now the latest(and last) satellite of a second group of Eorsat (ELINT Ocean Reconnaissance Satellite) satellites which has been launched into a circular 800km 65degrees orbit. It is believed that they used an experimental 'Topaz' nuclear reactor to power their operations. The first group of Eorsats are launched into a lower 410km 65 degrees orbit and use more conventional energy. They are still being used today and the last one to be orbited was Kosmos 2326 (1995-71A/23748).
Kosmos 1818 (1987-11A/17369) was the first Eorsat in this higher orbit which has been observed closely by many observers as this one has been spinning and accelerating during several years. It is believed that it was loosing nuclear fuel in its orbit and this could be the reason to its acceleration.
Maybe all this is happening now to Kosmos 1867(1987-60A/18187)
Note that Kosmos 1818 and its flash period behaviour have been studied extensively in Flash a few years back. A compilation of what happened is provided by this SeeSat-L message by Leo Barhorst:
The Lincoln Laboratory's Haystack radar system near Boston supported a NASA research in charaterizing the size of space debris. They detected that the Cosmos 1900 spacecraft, is leaking coolant (sodium potassium) from its nuclear power source. Cosmos 1900, a Radar Ocean Reconnaissance Satellite using a nuclear reactor to power its surveillance equipment, was launched in december 1987, but suffered a boost problem that left it in a lower than planned orbit. One year later the satellite was turned off and transferred to a higher orbit.
To which Bart De Pontieu replied:
Rainer Kracht may have been as surprised reading this as I was. Rainer wrote an article in 'Flash' of April-May 1993 reporting on the flash period behaviour of Cosmos 1818 (87- 11 A, 17369). The nature of the mission of this satellite (and its twin sister Cosmos 1867, 87- 60 A, 18187) was unknown, but similarities with the RORSAT satellites were evident, and by January 1989, soviet scientists confirmed that they were test flights of the TOPAZ nuclear reactor.
Observers noticed a regular light-variation of Cosmos 1818 in the middle of May 1992. Bram Dorreman was the first to report a flash period of 5.9 sec. [See the graph of the evolution of the flash period from May 1992 till now]. The rotation of the satellite accelerated continuously until a flash period of 3.6 seconds was reached in September 1993. The acceleration halted at that point, and the flash period has been steadily rising until Mike McCants observation of October 1995 which puts it at 4.23 seconds.
As Rainer mentioned in Flash in 1993, 'this kind of behavior is kind of rare for a payload, so two explanations are probable :
1. left-over fuel is being gassed out by the 'in-orbit maneuvering stage'
2. the reactor is losing gaseous products of radio-active decay.'
These were only speculations at the time, but Leo's message confirms that option 2 has happened with other TOPAZ reactors, so it seems highly probable that this reactor was venting radio-active products as well.
Who needs an expensive radar to figure out what happens to satellites ?
It may be worthwhile to monitor the other reactors for flash period accelerations.
I have checked the ortital elements since May 92. Because I have no elements from before May 92 when it started flashing, I cannot determine if there was also a change in the orbital elements. But between 18 Oct 93 and 2 Nov 93, the semi major axis decreased suddenly with 250 metres.
It is rather strange that this is not reflected in the evolution of the flash period.
Both objects need to be followed closely!