|
 |
| The CSIRO Parkes Telescope as it appeared in the early 1960's. (Image: CSIRO) |
For reference, see my previous report on the Parkes Mariner 2 tracks of December 1962.
In 1962, NASA had a plan to launch a spacecraft to Mars in November 1963
and deliver a 125-pound capsule to the surface of Mars in July 1964.
However, NASA postponed this
mission in favour of a fly-by experiment which subsequently became the
Mariner 4
mission. A network of tracking antennae around the globe, known as the Deep
Space Instrumentation Facilities (DSIF) was to provide continuous
communication with the spacecraft. When the mission was first
proposed, it was envisaged that the planned
Goldstone 210-ft antenna (DSIF 14) would be built and ready in time to track the spacecraft
at Mars. It was consequently given the moniker, "The Mars
Dish". However, delays in construction meant that by
the time of the Mariner 4 fly-by of Mars on 15 July 1965, the Goldstone
dish was still about a year from completion. Consequently, Parkes
was approached to provide a 210-ft capability as a backup to JPL's
fledgling Deep Space Network (DSN). This was also, the first space
mission for the newly commissioned tracking station at Tidbinbilla,
with its 85-ft antenna (DSIF 42). The station is today known as the Canberra Deep Space Communication Complex (CDSCC).
 |
Delays in construction meant
that the 210-ft Goldstone dish wasn't completed until May
1966.
Left: Tidbinbilla in 1965 with its 85-ft antenna (DSIF
42). (Image courtesy of Colin Mackellar).
Right: The 210-ft
Goldstone dish under construction (DSIF 14). (Image: CSIRO) |
The objectives of the experimenst for Parkes were to demonstrate the
performance of the 210-ft dish for the reception of data from distant
spacecraft, to record the picture transmissions during the critical
post-encounter period and, if possible, to observe the occultation of
the spacecraft by Mars on 15 July.
Mariner 4 carried an S-band transmitter centred on 2300 MHz. The GSDS
960 MHz receiver, previously loaned to Parkes for the Mariner 2 tracks
in December 1962,
was converted to operate at the higher
frequencies, and a parametric amplifier from JPL was installed to
increase the sensitivity of the receiver. In addition, a circularly
polarised feed was constructed. The data rate from Mariner 4 was just 8
bits per second, and the receiver had a bandwidth of 11 Hz. Pointing and
frequency predicts as a function of time were telexed to Parkes on a
daily basis. As with the Mariner 2 test tracks, Harry Minnett and Doug
Cole were responsible for the Parkes operations, and the cost of the
tracks was assumed by the NASA research grant, NsG-240-62.
 |
The JPL 960 MHz phase-lock receiver at Parkes was modified to operate at the higher frequency of 2.3 GHz. (Image: CSIRO) |
On June 21, Parkes began receiving the Mariner transmissions. Daily
tracks were carried out during two-hour periods each afternoon centred
approximately on Mariner's meridian transit.
Horizon-to-horizon observations were obtained on July 3, 14, 15 and 16.
Regular telemetry recordings were made from July 8 to August 27. The
telemetry was recorded on a Pemco instrumentation tape recorder using 5½
inch reels with a play time of about 30 minutes.
The closest approach to Mars was scheduled to occur about 2 ¼ hours
before it rose above the Parkes telescope's 30 degree-elevation
horizon on 15 July. Soon afterwards, the spacecraft
was targeted to pass behind the planet (occulted) when it was still one hour from rising
at Parkes. The exit from the occultation was predicted to occur when the
spacecraft was still 11 minutes from rising above the telescope's horizon. These occultation observations were considered
important since they were intended to probe the atmosphere and
ionosphere of Mars as the signal disappeared behind the planet and
then re-appeared on the other side. There was uncertainty in the precise timings of the
occultation (this being the first time it was ever attempted); the
exit could have occured either just below or just above the telescope's
horizon. So, just in case it occured below the horizon, it was
decided by the Parkes team to perform the exit observation with an off-set
feed to allow the signal to be detected in the few minutes before it was
to rise at Parkes. However, as it so happened, the exit from the
occultation occurred just above the telescope's horizon. Consequently,
considerable
difficulty was experienced in tracking the spacecraft with the off-set feed for
the remainder of the track.
None-the-less, valuable experience was gained by this exercise, which
proved crucial four years later during Apollo 11.
The experiments on Mariner 4 with the Parkes telescope showed that the
210-ft dish equipped with a standard S-band parametric amplifier had a
margin of about 2.5 db over a maser
equipped 85-ft dish. The resulting gain in data transmission performance
was demonstrated. Using identical receivers on the 85-ft antennae
at Woomera's Island Lagoon (DSIF 41), and at Tidbinbilla (DSIF 42), the increase in
performance with the 210-ft dish at Parkes was close to the
theoretical figure of 7.7 db (an approximately 6 times stronger signal).
 |
| Theoretical and measured powers
received from Mariner 4 on 210-ft and 85-ft antennae (41= Island Lagoon,
Woomera and 42=Tidbinbilla). |
In early September, the tapes with the telemetry recordings were shipped
to JPL. The tapes contained the data for the 22 images of the Martian
surface captured by Mariner 4. The Parkes data was combined with the
data from the smaller 85-ft antennae to produce a considerable
improvement in the quality of the pictures of the Martian surface. The
images showed the surface covered by craters, similar to the Moon. This
disappointed, and surprised, the astronomers since they were expecting
to see verdant forests with lakes and oceans covering the planet.
Click here to read the report on the "Initial Scientific Interpretation of Mariner 4 Photography" by Leighton et al - 4 August 1965.
 |
| Image number 11 was the best, and most dramatic, of the 22 Mariner 4 images of the Martian surface. (Image: NASA). |
On 15 July 1965, the historic, first mission to Mars, changed forever the way we see the "red planet".
The mission was an outstanding success, returning the first ever photos
of another planet from space. It also, demonstrated the performance and
suitability of large tracking antennae, like Parkes, to space
exploration.
Click here to read the official report of the Parkes Mariner 4 track
"Observations of Mariner 4 with the Parkes 210-ft Radio telescope - RPL 173" by D.J. Cole and P.R. Crosthwaite, CSIRO Radiophysics Laboratory.
John Sarkissian OAM
CSIRO Parkes Observatory 15 July 2025
|
