Radio systems of the Zond 4-8 series of spacecraft
Deductions from external features of Zond spacecraft
Zond and Soyuz share the same basic design, but there are differences between
the craft. The differences in outward appearance between Soyuz and Zond
that relate to radio systems can be summarized as follows:
The Zond has no orbital module, but instead a small inverted conical unit
a dish antenna with a diameter of 1.2 meters for the main downlink on 922.76
MHz and possibly also for receiving commands on 768 MHz. On 922 MHz the
beamwidth of this dish is about 20 degrees. The earth subtends an angle
of 1.7 degrees when viewed fom the moon.
two small antennas on ground planes. These small antennas look like cylinders
with about 5 cm diameter and 5 cm height and may contain a a half-wave
loop. The may be omni antennas intended for 922.76 MHz.
There are two devices that look like a large handle on each side of the
Zond equipment module. The length of the "handle" is about 1.0 meter. If
this dimension represents half a wavelength then this antenna could be
intended for the 115 MHz uplink and 183.6 MHz downlink of the old Soviet
deep space TT&C system.
The two spacecraft are similar in that there is a ring of dipoles around
the base of the descent module. This antenna is the command reception antenna
for 768 MHz.
Whip antennas on the Zond solar panel tips are about half the length of
those on the Soyuz and mounted on the rear edge of the panel instead of
on the front edge. These whips are each about 2.0 meters long. If they
have the same electrical length as those on Soyuz then they are a quarter
wavelength long, i.e. cut for a wavelength of 8 meters, i.e. about 38 MHz.
If the whips are cut for half a wavelength, then the frequency is 76 MHz.
Information from other sources
Very little information is available in the public domain about frequencies
used by the Zond system. Only informal information is available to support
the assumption that a 922.76 MHz downlink was used. Informal hints from
personal acquaintancies mention 183 MHz as a downlink. The analysis of
the pictures of Zond seem to support the use of the 922/768 MHz and 183/115
MHz TT&C systems. However, the whip antennas on the solar panel tips
are difficult to tie to a specific downlink frequency. It is difficult
to envisage that 76-80 MHz was used in deep space, since the "Tral" telemetry
system that used this frequency range was a wideband system operating in
low earth orbit. It seems more reasonable to assume that the whips were
used for a frequency near 40 MHz, perhaps the same type of simple telemetry
that was transmitted by the early Luna probes on 39.986 MHz.
It seems reasonable to conclude that the main telemetry, command and tracking
link used by Zond 4-8 was the 922.76 MHz downlink with the uplink at 768
MHz. In addition a back-up system using omni antennas seems to have operated
on the old Soviet deep space TT&C system that used 183.6 MHz as a downlink
and 115 MHz as an uplink. Perhaps 40 MHz was used for very low rate housekeeping
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