Radio systems used by the Luna 15-24 series of spacecraft

Sven Grahn, Sollentuna, Sweden

Main telemetry/command link

The spacecraft bus that landed on or orbited the Moon carried one or more conical helices that were probably intended for the standard 922 + 768 MHz telemetry and telecommand link. See picture below.

Back-up spacecraft bus link and main return craft link

The Luna 16 lunar orbiter/lander bus and earth return craft each carried two sets of rod antennas The size of these rods were measured by enterprising persons at an aerospace exhibition where the Luna 20 spacecraft was displayed. The figure below shows the result of these measurements.  Let assume that the antennas are quarter wave rods fed part of the way up from the "ground" end. If that is so, then antenna AA' is resonant at the frequency fA=300/(4 * 0.36)=208 MHz. The corresponding frequency for the BB' antenna rods is f´B=300/(4 * 0.57)=131.6 MHz. It is probably safe to assume that the antenna system is operating a lower frequency than calculated here. Let us assume that antenna AA' operates at 183 MHz, then one would have to apply a correction factor to the frequency of antenna BB' equal to the ratio (183/208)=0.88. If this is a correct way of reasoning then the BB' antenna worked on 0.88*131.6=115.8 MHz. Howeveer, recent data on the new webpage of the Lavochkin association shows that the uplink was 101.965 MHz!

In (1) the wavelengths 1.6 m and 2.5 m are mentioned for the Luna series. 1.6 meters probably refers to 183.6 MHz (which is precisely 1.634 m). The wavelength 2.5 meters corresponds to 120 MHz. But, in connection with the flight of Luna 15, the Soviet Union told NASA (2) that the frequency 115 MHz was used. It is not clear of this was the up- or downlink even though (2) indicates that it is the downlink..
 
 

Landing radar

The landing radar system operated on 10 GHz according to Krupenio (3). The picture below shows the radar antenna in its stowed position on the landing module. (The picture below has been obtained from the Web site of  Alexander Chernov's Virtual Space Museum).
 

References

  1. S.P Korolev (edited by M Keldysh), "The Creative Legacy of Academician S.P. Korolev", Nauka, Moscow 1980, p.402.
  2. Aviation Week & Space Technology, 28 July 1969 ("Soviet Luna 15 hard-lands in Sea of Crises")
  3. N. N. Krupenio, "Methods of Radar investigations of the Moon and planets using spacecraft" in "Apparatus for Cosmic Research", Space Research Institute, Akademia Nauk, SSSR, Nauka Publishing House, Moscow, 1972.

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