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Zenit - Korolyov's Legacy

Tyneside, UK
2022 Aug 15
Monday, Day 227

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History of Zenit Recovery Beacons

The first identification of a recovery beacon transmission from a member of the Zenit family was in 1966. On April 14, Geoff Perry at Kettering, and Sven Grahn in Stockholm, both heard what appeared to be a morse code transmission of the letters "TK". The transmission followed the cessation of conventional signals from Cosmos 114 as it headed for re-entry and recovery. That was the beginning of many years observing radio signals from Zenit spacecraft descending under their parachutes.

Sven Grahn provides a description of the signals on his web site. He also extends the historical record back to 1965 through his links with Dieter Oslender in Bonn.

1966-1968 - First Impressions

They were called "TKs" because that is what they sounded like, but it was soon apparent that the morse code dash of the 'T' was sixty percent longer than it should have been. TKs were observed at Kettering from Zenit re-entries between spring and autumn of each year. The winter months were a dead period because signals would only propagate when the lower ionosphere between the landing zone and Kettering was in sunlight. Even then, observations were not always forthcoming.

One thing that was noted was the absence of TKs from re-entries of a particular vehicle type. Geoff Perry noted that recovery beacons were never intercepted from satellites that were classified as having a "Mode 1" telemetry signature while in orbit.

1969 - A New Development

A variant of the TK appeared in the form of 'TG'. What is more, the TG beacon was associated with 'Mode 1' telemetry. It seemed the missing satellite type had turned up. The question was why they had not been detected previously.

The original TK transmissions were at 19.995 MHz, and the newly-discovered TG was transmitted at 20.005 MHz. That leads to a possibility that the Mode 1 satellites (we now know them to be the original Zenit-2) had been transmitting TG at 20.005 MHz since the first launch in 1962.

The answer to why the TG beacons were not found earlier may lie in a Kettering observing technique from its formative days. In order to avoid mistuning the receiver and missing a beacon, Geoff Perry insisted on a strictly "hands off" policy during a recovery. When the satellite transmission faded out, the receiver would remain tuned to precisely the same frequency ready for the recovery beacon. It excluded any possibility of checking other frequencies during the parachute descent even if no signal was observed. It originated from the fickle tuning arrangement of the team's original war-surplus Marconi CR-100 receiver.


Apart from the period around 1969-1970, the use of the various beacons (TG, TK, TF and TL) follows a simple sequence.


The Zenit-2 and Zenit-4 came into service at about the same time and it looks as though they were allocated TG and TK respectively. When the Zenit-2M appeared, it used TK briefly but took over TG after the Zenit-2 was phased out. An explanation might be that Zenit-4 beacon hardware was used in the prototype/developmental Zenit-2Ms but, alternatively, maybe someone just decided to bring order into that particular aspect of the programme.

TG disappeared with the demise of the Zenit-2M.


Zenit-4's TK beacons were the first to be tracked by the Kettering Group but TG beacons probably pre-date them. While they existed side-by-side, the Zenit-4 and Zenit-4M both used TK. When the Zenit-4M series was wound down during 1974-5, the Zenit-4MKT took over the TK slot. When the Zenit-4MKT reached the end of its life, TK fell out of use.


The TF variation appeared in 1969 with the Zenit-4MK. When the Zenit-4MK was phased out in 1976-7, the TF beacon was transferred to the Zenit-4MKT and Zenit-6 to use in parallel. It was later taken-up by the Zenit-8 in 1984, and subsequently saw out its days as the only Zenit beacon type used until the end of the program in 1992.


Standing to one side was the Zenit-4MT that carried out high-altitude cartographic missions from near-circular polar orbit. It used TL as a beacon for the whole of its working life between 1971 and 1982.

Page Date: 2011 Sep 14

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