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The Kettering Group

Tyneside, UK
2024 Jul 24
Wednesday, Day 206

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Geoff Perry item

Soyuz & Salyut - article by Geoff Perry

BBC News Feature

Letter Announcing the Existence of Plesetsk

This is Geoff Perry's letter to Flight International announcing that Cosmos 112 had been launched from somewhere other than Tyuratam (as we knew it then). Pinpointing the actual location and its name were still to come.

The letter was published in the issue of the magazine dated 1966 April 21 and, interestingly, it reveals something else that is only obvious in hindsight:

Flight International letterNew Cosmos Launch Site?

SIR,—Radio signals from Cosmos 112 were received in Kettering at the end of the second and third revolutions on March 17 and again on the following two days. Apart from the usual 19.995Mc/s signals, characteristic of the recoverable eight-day Cosmos, it soon became apparent that there were departures from the normal. One marked difference was the orbital inclination of 72.1°. The launch was unusually late, at 1035 GMT. Signals were not received on the usual five or six passes each day, and those which were received were weak and of short duration, suggesting that they were commanded-on when the satellite was much farther north than usual. Finally, the period was 92.07 min, the same as that of Cosmos 98.

Opinions have been expressed that this is an arbitrary period, possibly due to an unintenional variation of the launching technique. I take the view that it is a carefully calculated period, designed to reconcile a higher orbit with the usual recovery area, after eight days. Calculations show that the optimum period for recovery after 124 revolutions in the usual area is 92.08min.

The RAE Table of Artificial Earth Satellites gives the lifetime of Cosmos 112 as 7.79 days. Division by the orbital period shows that recovery occurred towards the end of the 122nd revolution. This implies that either the launch or the recovery, or both, occurred in different areas for the two satellites.

Multiplication of the track separation of 23.24° by 31 gives a product of 719.44°; nearly two complete Earth rotations. This suggests that the sub-satellite tracks will repeat themselves every 31 revolutions — a suggestion borne out by the prediction sheet published by the Radio and Space Research Station. Further examination of this sheet confirms that the launch could not have originated from the Aral Sea complex.

It appears that the initial orbit of Cosmos 112 had a northern apex at 1038 GMT at a longitude of 90°E. It has been suggested to me by a fellow-observer, Sven Grahn of Stockholm, that a launch from the southern tip of Novaya Zemlya (71°N, 52°E), would satisfy all the foregoing observations, and I am inclined to agree. Signals received from Cosmos 114, launched on April 6, show certain similarities to those from Cosmos 112. Although I do not have full information at the time of writing, I assume that, as the orbital inclination is 73°, it originated from the same "new" launch site. The fact that only the last part of the transits are received suggests that this satellite is being commanded from the northern site as well.

The Grammar School               G. E. PERRY
Kettering, Northants

The letter does not hit the exact spot for Plesetsk (62°.9 north, 40°.5 east) but there was not much to go on so it was pretty close until analysis of the Cosmos 114 ground track allowed a more precise location to be calculated.

In a piece of writing typical of Geoff, what he purposefully did not say is as significant as what he did!

In 1966, March 17 was a wednesday so the description of signals received covers only as far as the friday, after which school was out for the weekend. On returning to school on monday March 22, the sunday-launched Cosmos 113 would have been occupying 19.995 MHz with nothing to be heard from Cosmos 112 because it had changed its transmission frequency - hence Geoff's carefully-worded opening sentence.

Cosmos 112's undetected move to 19.990 MHz was probably the first time that a satellite changed frequency to allow the newcomer access to the main frequency, though it became clear with later launches that it was the norm. It's just that the transmissions on the alternate frequency were not detected on that occasion but Geoff's words hold the clue that points to it having happened.

page date: 2010 Jun 12
updated: 2013 Sep 9

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