Development of the Luna sweeping-carrier ranging system

I stumbled upon an excellent description of the sweeping-frequency ranging system used by many Soviet deep-space missions when reading Roads to Space (1, see dust cover on the right). In one of the oral histroical accounts Leonid Ivanovich Gusev, the Director General and Chief Designer of the Russian Scientific Institute of Space Instrument Engineering (RNIIKP), formerly known as NII-885:

"....Our main preoccupation was the radio link margin on which the accuracy of trajectory measurements as well the data transmission rate and volume depended. There were several ways of improving the link margins, for example by increasing the transmitter power, or the receiver sensitivity. Alternatively, we could have moved to much higher frequencies. But these straightforward solutions were time-consuming and very expensive. A better way forward was proposed by Y. Y Boguslavskiy, who had invented a method of determining the slant range to a spacecraft by uplinking a carrier with a rapidly changing changing carrier frequency. The uplinked carrier was turned around by an onboard transponder and retransmitted to the ground, where he slant range was determined by using differential frequency analysis. Boguslavskiy's method used very narrow bandwidths which could be tracked by phase/frequency converters. Since the background noise level is inversely proportional to the bandwidth, a very good signal-to-noise ratio was achieved which favourably influenced the link margin.

I had the opportunity to develop the instrument that generated those sweeping carrier signals. It was a custom-made computer which controlled the sweep using frequency synthesizers, determined the phase difference between the signals in the uplink and downlink, and solved the equations that yielded the speed and distance of the spacecraft. As head of our laboratory I not only developed the equipment but also supervised its manufacture and subsequent installation at the TT&C stations in Simeiz and Simferopol. The computer supported spacecraft flights to the Moon, Mars, and Venus. The lunar mission included taking pictures of the Moon's surface, steering the Lunokhod rover and bringing back soil samples to Earth. ......."

L.I Gusev, in "Roads to Space, An oral history of the Soviet Space program", Aviation Week Group, 1995, p.426

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