July 17, 2009

Parkes Observatory during moonwalkThe first manned mission to land on the moon had an Australian connection. The 64-metre Parkes Radiothermal Telescope, still the largest steerable dish in Australia, had only been in existence for eight years when Apollo 11 was launched. It was one of three tracking antennas to receive the original television signals from the lunar module, the other two being the 64-metre Goldstone antenna in California and the 26-metre Honeysuckle Creek antenna, near Canberra. Parkes' staff fought high winds and the risk of serious personal injury to keep the dish pointed at the moon and deliver the best quality picture of the three. So superior was the Parkes' picture that after the first nine minutes, the remaining hours of the broadcast were sourced through Parkes -- and were subsequently lost by NASA.

No fault should be ascribed to NASA because of this. The original Parkes signal consisted of telemetry data and an SSTV video feed. The SSTV data, in turn, was split into two parts: the first recorded on data tapes, the second converted for broadcast to televisions all over the world -- not electronically, but by pointing a conventional television camera at a monitor displaying the SSTV images. This second version remains as videotape and kinescope; but it has the reduced quality and noise one would expect of a film of a film, not to mention further distortion due to normal analogue transmission over a long transmission path. This was another reason NASA had hoped to use the closer Goldstone station, but those pictures turned out to be extremely poor quality.

On top of all this, archiving standards in 1969 were not what they are now: and 10% loss was considered normal. For all its standards and upgrades, modern archiving does not do much better. With the current amount of previous and constantly added data in the system, we are running into the butterfly effect: where the effect of any errors or other perturbations grows exponentially to the point where the behaviour of this dynamic system begins to appear chaotic. In practical terms, 3-5% of all data in modern archives will be inaccurate. Further, any attempt to fix an inaccuracy will itself induce other inaccuracies.

In a budget-consciousness which modern sensibilities should find familiar, old SSTV tapes -- which were extremely expensive -- were also routinely erased and reused. The original SSTV tapes which had been shipped from Australia to Goddard were no exception -- and after Goddard received the tapes, there was no reason for Australia to hold onto the backup copy. It was the height of the Cold War, and there were other priorities. Anyway, it was obvious now to all involved that it could only be a matter of a few decades now before a permanent manned station would be established on the moon.

On the plus side, at least we know that the old technology can still be read if found. Other telemetry tapes from the same period have been discovered at the Curtin University of Technology in Perth, and have been successfully read.Parkes radio telescope at night

Thanks to NASA's frame by frame restoration of the original video footage, some of which has been in storage since the original moon landing, we also know that modern technology can do an amazing job of restoration of the original video footage.

The Parkes radio telescope continues to be a tracking link for space missions to the present day. Mariner 2, Mariner 4, Voyager, Giotto, Galileo, and Cassini-Huygens are all being tracked in part by Parkes. Other radio telescopes have since been built, some of them arrays of dishes which together are much larger than Parkes; but if another manned mission to the moon once again becomes possible, Parkes will almost certainly have a part in it.

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