Radio systems of Soviet Mars and Venus probes

Official descriptions of the radio systems

Venera 1:
When Venera-1 was launched in February 1961 Soviet news media announced that the probe transmitted on 922.8 MHz. The tradition of publshing transmission frequencies started with early space launches contined. The idea was probably that foreign radio observatories could pick up the transmissions and thereby verifying any possible claims of Soviet authorities as to the final fate of the spacecraft

Mars-1:
For Mars-1, launched in November 1962, Soviet news media provided the following brief description of the probe's radio systems:

"The craft carries three radio systems, working on wavelengths in the metre (1.6m), decimetre (32cm) and centimetre (5 and 8 cm) ranges....The radio complex working in the metre range serves both for transmission of telemetric information about condition of the station and for maintaining communication with the earth in the event of abnormal functioning of the orientation system."  (1)

No precise numbers were given this time, but the numbers provided still gave a clue to the actual frequencies. We now know that this text should be interpreted so that the main radio link from Mars-1 to earth operated on 922.76 MHz ("decimeter" or "32 cm band"). We also know that the corresponding uplink from earth worked on 768.96 MHz (refrred to in Soviet literature as the 39.cm band). The "metre-band" back-up link worked on 183.6 MHz down and the uplink was probably near 102 MHz as it was for early lunar probes. It appears that the metre band was only used for the 2MV spacecraft. For radio science measurements near Mars a signal coherent with the main 922.76 MHz link  was transmitted on four times that frequency, i.e. on 3691.04 MHz - the "8 cm band". In addition there was an additional link in the "5 cm-band" which we now know meant the 5840-5890 MHz range. The omni antenna for 32 cm is probably of the design shown in Picture 4 (this picture was taken by myself in the Energia museum in Moscow).

Zond-1, Venera-5,6,7,8
Soviet media gave the transmission frequency of Zond-1 as 922.76 MHz and of Venera-5 and 6 as 922.763 MHz. The transmission frequencies of Venera-7 and 8 were given as 928.429 MHz.

Modulation systems

The metre band link
Very little is known from Western sources about the modulation scheme of the metre band transmissions from interplanetary probes. Metre band radio systems were most probbaly used only by the 2MV series of space probes. According to(6) PCM-FM-AM was used on the uplink and PCM-PM was used on the downlink. The rightmost modulation method denotes the modulation of the main carrier. 

For Mars-1 Moscow sent a message to Jodrell Bank  (2) giving details about the modulation used on one of the radio systems of Mars 1:

"The telemetry transmitter operates on 922.8 MHz with +/- 120 deg phase modulation with the subcarrier frequency in the range 1100-1700 Hz, during telemetry transmission the subcarrier frequency is modulated in frequency by a code signal."

For the M-69 Mars project the 32/39 cm link was designed to receive radio commands, to measure the radial distance and velocity, and to transfer the telemetry data. The onboard transponder operated at 100 watts of power, and data were transmitted at a rate of 128 bits/sec The telemetry system, designed with 500 channels to provide the data from the onboard systems.(3). In (7) details are given in graphical form about the data rate and signal spectra for this telemetry system showing how subcarriers were modulated by the pulse-code-modulated data stream and then phase-modulated on the main carrier.

For Venera-4 (4) indicates that the decimeter radio system transmitted telemetry data to Earth at speeds 1, 4, 16 and 64 bits per second. Power of the decimeter transmitter - was 40 watts.

In (11) Don Mitchell writes: "...at some point, probably beginning with Venera-9, the modulation scheme was changed from frequency shift keying to phase shift keying . In this system, binary zero and one are represented by 180° differences in phase. PSK is more energy efficient than FSK,"

For Venera-4 (4) indicates that the decimeter radio system could receive up to 127 discrete commands from Earth. In later versions of the comand system not only simple functional, discrete, commands could be sent, but also numerical data (digital data such a software) (6) .

The 8-cm link

According to (11) a 20-watt, 200 pixel/sec PPM image telemetry system was designed for the Zond-2 Mars mission. Alternatively, it could transmit images on 8-centimeters with frequency shift keying, at 512, 1024, 2048 or 4096 bits/sec.

The 5 cm link

Impulse modulation
The modulation is described in (3) as "impulse modulation". For Mars-1 the image data would be tranmitted at approximately 90 pixels/sec, using pulse-position modulation in 25 kilowatt spikes. The average power consumption was 50 watts (10).

For the M-69 project the impulse transmitter was designed to transmit images of the Martian surface to Earth. It operated at a power of 25 kilowatts (per pulse), and data were transmitted at a rate of 6,000 bits/sec (3) . It appears from (6) that Pulse-Position-Modulated (called Pulse-Time-Modulation in Russian terminology) were transmitted on 5844 MHz. By examining the signal spectrum shown in (7) one can draw the conclusion that the pulse width was about 0.83 µs.

According to (11) the Mars missions, M-69 (which was destroyed at launch) and Mars-2 to Mars-7 used several telemetry systems, including 1024 pixels/sec (about 6144 bits/sec) image transmission with PPM on the 5-centimeter band and science data at 128 bits/sec with continuous-wave FSK. Venera-9 returned the first images of the surface of Venus, using a digital FM system at 256 bits/sec on each of two camera channels. After the 1973 Mars missions, the use of pulse position modulation was discontinued.

Phase modulation
The frequency given here for the 5-cm link (5.87-5.89 GHz, center frequency 5.88 GHz) comes from (5) . In (6) data are give for the Fobos missions. The phase modulation of the encoded 16 384 bps data is ± 1.3 rad, transmitter power 50 watts at 5885 MHz. The corresponding uplink is given as  5008 MHz. The Fobos missions were the first utilizing this combination of up and downlink.

Venera-15: A radio link at 5 cm wavelength provided a data transmission rate of 100 kbits/sec from the spacecraft to Earth at all distance up to the maximum of 260 million Km.

Landing probe links

Early landers - a direct-to-earth link
On the early landers (Venera-2 to -8) scientific data from the landers were transmitted directly to earth on the 32-cm band link. A relay through the main spacecrfat was difficut to arrange because the main spacecraft could have burned up in the planet's atmosphere or crashed on its surface by the time the landing capsule touched down. It also seems that the same frequency as that of the main spacecraft was used also for the landers. The reason for this assumption is that Jodrell bank picked up signals from the descent vehicle of Venera-4 on the same frequency as the main spacecraft. The antenna on the lander needed to have low gain in order to ensure that the link to earth was not blocked. This, and the very long distance to earth, led to very low data rates (1 bit/sec) from the descent and landing on Venus. Cleraly such a low transission rate would not be sufficient to transmit any pictures from the surfec during h evry short lifetine of the lander (approximately an hour) on the surface of Venus. The use of the 32-cm band for the lander-earth link is logical because the antenna size on earth is fixed and the antenna gain on the lander is fixed. In such a case the basic link budget is independent of frequency.

Later landers - relay through the main spacecraft
For the 4V and M-71 landers and following spacecraft models the signals from the landers would be relayed through the main spacecraft, either during a flyby or while in orbit around the planet. The frequency of this intersatellite link needed to be as low as possible. It can easily be shown that when communicationg between two antenna with fixed gains (determied by providing sufficient coverage) the frequency should be chosen to be as low as practically possible (the size of the antennas may be limted by geometrical concerns) (9). In (6) the frequencies used by lander to main spacecraft link are given as122.8 MHz and 138.6 MHz. It appears that each of the two frequencies carried data from a different camera.

Venus: According to (11) there was a 512 bit/sec connection from the Venera lander and a 3072 bit/sec connection to earth, the orbiter relayed data in real time and also recorded it on tape for several later playbacks. In (6) the data rate is given as 3072 bits/sec transmtted on a subcarrier at 30,72 kHz. In (10) the data rate to earth is given as 3072 bits/sec. 

Mars:According to (3) data from Mars landers would be transmitted to the Martian satellite at a speed of 72,000 bits/sec in two independent radio channels. The circular panoramic images of the landing site would be transmitted as an image of 500 x 6,000 pixels. Each minute the video information would have to be interrupted by the telemetry data. The period calculated for each communication session would be 18-23 minutes. After the first communication session, the onboard transmitters would be disconnected and the station transferred to a survival state. The second communication session would be initiated by a transmitted signal. Its period would depend on the position of the landing site and could be 0.7-5 minutes.

Also according to (11) the cameras scanned back and forth, sweeping out a 115 × 512 pixel panorama, which was digitized to 6 bits per pixel, with a 7th parity bit. A small images size (compared to Luna-9's 500 × 6000) was motivated by telemetry rates and an estimated 30-minute minimum lifetime. Two meter-band channels carried 256 bits/sec each, a conservative rate dictated by a low target error rate and the semi-directional transmitting antenna.

The Fobos spacecraft was intended to land an autonomous station of the Marian moon. It would communicate with Earth on 1672 MHz. The PROP-F "hoppers" may have used 280 MHz return link and 401.5 MHz forward link - I think.

The Mars-96 spacecraft carried "penetrators" that used the international standard 401.529/437.1 MHz link.

Frequencies used

The table below summarizes my knowledge of frequencies used by Soviet/Russian interplanetary probes. Numbers maked red come directly from Soviet media reports an later post-Soviet literature. Data from Joe Bruman at JPL marked blue. Numbers marked green come from the Library of Congress reports on the Soviet space program.

Spacecraft	Purpose	Flight	Metre band MHz	32/39 cm MHz	8 cm MHz	5 cm GHz	X-band GHz	Lander-probe	Lander-earth
Venera							-
1VA	Venus impact	Venera-1	-	922.8 /769	-	-	-	-	-
2MV-1	Venus landing	25 Aug/1 sept 62 failures	183.6/101.9	922.76/768.96	3691.04	5.84?	-	-	922.76
2MV-2	Venus photo flyby	Sept 12, 1962 failure	183.6/101.9	922.76/768.96	3691.04	5.84	-	-	-
3MV-1A	Venus test flight	Kosmos-21, Feb 19, 1964	-				-	-	922
3MV-1	Venus landing	K-27, Zond-1	-	922.76 /768.96			-	-	922.76
3MV-2	Venus photo flyby	Venera-2	-	922.763 /768.969			-	-	-
3MV-3	Venus landing	Venera-3	-	922.763 /768.969			-	-	922.76
1V	Venus landing	Venera-4	-	928.4/773.7			-	-	928.4
2V	Venus landing	Venera-5,6	-	922.763 /768.969			-	-	922.763
3V	Venus landing	Venera-7,8	-	928.429 /773.691		5.895	-	-	928.429
4V-1	Venus landing	Venera-9,10	-	922.763/768.969	3691.04		-	122.8 & 138.6	-
4V-1	Venus landing	Venera-11,12	-	928.4/ 773.7	3713.6	5.859	-	122.8 & 138.6	-
4V-1M	Venus landing	Venera-13,14	-	928.4/773.7?			-	122.8 & 138.6	-
4V-2	Venus orbit	Venera-15,16	-	928.4/773.7?			-	-	-
5VK	Venus landing	Vega-1.2	-	928.4/773.7?			-	122.8 & 138.6	-
Mars							-
1M	Mars flyby	Oct 1960 failures	-	922.8/770	3691.2	-	-	-	-
2MV-3	Mars landing	4 Nov 1962 failure	183.6/101.9 MHz	922.8/770	3691.2		-
2MV-4	Mars flyby	Mars-1	183.6/101.9 MHz	922.76 /768.96	3691.04	5.84	-	-	-
3MV-4A	Mars photo flyby	Zond-2 (Zond-3 to moon)	-	922.763/768.969	-	5.84	-	-	-
M71	Mars orbit & land	Mars-2,3	-	928.4 /773.7	?	5.84	-	122.8 & 138.6	-
M73	Mars orbit	Mars-4,5	-	928.4/773.7?	?	5.84	-	-	-
M73	Mars flyby & land	Mars-6,7	-	928.4/773.7	?	5.84	-	122.8 & 138.6	928?
1F	Mars orbit	Fobos-1.2	-	928.4/773.7	-	5.885/5.008	-	280/401.5?	1672
M1	Mars orbit & land	Mars-96	-	-	-	5.008?	8.427	401.529/437.1	-

Antennas used on various spacecraft models 

1VA (Venera-1)

Picture 1: Venera-1, 1VA, launched on 12 February 1961 was the first successful vehicle that used the new decimeter.band radio systems. The news agency TASS announced the transmission frequency as 922.8 MHz. The rather detailed pictures of the craft that were released show no sins of antennas for any other frequency band, i.e. the 32/39 cm down/uplink system (922.8/769 MHz). The photo above shows two tunrstile antennas for the decimeter band an the high-gain paraboloc dish for the same frequecy band. All antennas were mounted on the shadow side of the spacecraft - the side of the craft was normally turned in the general direction of Earth. The fact that no cm-band transmitters were carried on the 1VA probe can probably be explained by the fact that no image transmissions requiring high bandwidth were planned for these early probes.

Picture 2: Venus probes (2MV-1) unsuccessfully launched in August and September 1962.

The antenna configuration show antennas for the metre and decimneter links. Presumably the cm link were served by the parabolic dish. The conical helices are not used for the 2MV-4 (Mars-1) craft where the hemispherical spiral antennas were used instead.

7 - low-gain antenna. 8 - antenna for monitoring the landing capsule. 9 - transmit antenna for the meter band. 10 - reception antenna for the meter band. 11 - omni antenna for emergency radio link. 12 - antenna for the surface section.

2MV-4 (Mars-1)

1. Pravda, 15 December 1962, "First flight to Planet Mars".
2. A telegram to Jodrell Bank  from Akademi Nauk in Moscow dated 10 January 1963 gave details about the radio systems of Mars 1.  The telegram was in Russian, but the Cyrillic characters were transcribed in latin letters. Dr Stas Barabash at the Swedish institute of Space Physics in Kiruna has helped me translate this telegram.
3. V.G. Perminov. The difficult road to Mars. A brief history of Mars Exploration in the Soviet Union.
4. Lavochkin Association web site about Venera-4.
5. RSA tracking system, Cross-support information, Russian Space Agency, 1993.
6. A.S. Vinitiski (ed.), Radio Systems of interplanetary spacecraft, Radio Communications, Moscow, 1993.
7. A description of the Kvant-D ground receiving system.
8. Don P Mitchell, e-mail dated 27 April 2011.
9. Planetary Landers and Entry Probes, Andrew J Ball et. sal, Cambridge University Press,, 2007, p.112. Available here.
10. SOVIET VENERAS AND MARS: FIRST RECONSTRUCTION AND SCIENCE, V Kerzhanovich, JPL,K. Pichkhadze, Lavochkin Association, Presented to International Workshop on Planetary Probe Atmospheric Entry and Descent Trajectory Analysis and Science, Lisbon, Portugal, 6-9 October 2003. Available here.

11. Don Mitchell's site on the exploration of Venus and other topics.

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