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| 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. When the mission was first proposed, it was envisaged that the Goldstone 210-ft antenna would be ready in time to track the spacecraft at Mars. It was given the moniker, "The Mars Dish". However, by the time of the Mariner 4 fly-by of Mars on 15 July 1965, the Goldstone dish was still about a year away 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.
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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. (Image courtesy of Colin Mackellar).
Right: The 210-ft Goldstone dish under construction. (Image: CSIRO) |
The objectives of this experiment 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, 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.
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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 below the Parkes horizon on 15 July, and soon after that the spacecraft was targeted to pass behind the planet when it was one hour from rising at Parkes. The exit from the occultation was predicted to occur when the spacecraft was still 11 minutes below the telescope's 30 degree-elevation horizon. These occultation observations were considered important since they were intended to probe the atmosphere and ionosphere of Mars. There was uncertainty in the precise timings of the occultation (this being the first time it was ever attempted), so it was decided by the Parkes team to perform the 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, on the day itself, the exit from the occultation occurred just above the telescope's horizon and considerable difficulty was experienced in tracking it with the off-set feed. 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, the increase in performance with the 210-ft dish was close to the
theoretical figure of 7.7 db.
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Theoretical and measured powers received from Mariner 4 on 210-ft and 85-ft antennas (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 antennas 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.
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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 antennas, 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
CSIRO Parkes Observatory 15 July 2015
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