A private tour of The Dish

Film poster and other
memorabilia on display
at Parkes

On the morning of December 28th, we were lucky enough to be in the company of the site's technical co-ordinator at the radio telescope near Parkes, Brett Preisig, who is also a keen aviator at the local flying club (Parkes Aero Club). He and his wife Sharon live in Parkes and we had met them for a drink in a local pub the previous evening, when Chris and he had also arranged to go flying, early on, before the thermals became problematic. Brett took Chris flying in his sports 'plane, "Flight Design 7884", and had then driven along the unsurfaced road to the telescope. George had brought Sha, Eddie and I the longer way round, on the Henry Parkes Way and Telescope Road.

The control tower is out of bounds to ordinary mortals, and to young children, so Sha stayed behind with Eddie at the Visitors' Centre, while the rest of us had the privilege of seeing the astronomers' premises. We went into a building where they kept the spare multibeam (13-beam), cryogenic receivers and the hard hats. Once we had donned these, we walked across to the tower to enter its Astronomers' Room and board room. The control room was on the next level up, full of (to me) mysterious equipment and computers, embedded or otherwise. The clock that's so essential to the detection work is unofficially called The Atomic Clock; it is a hydrogen microwave laser that loses track of no more than 2 nanoseconds per 24 hours. The master control panel (MCP) looks like an old style analogue machine, but actually works digitally, showing the Zenith (how far up the receiver is pointing) and the Azimuth (how far across the sky), if I have understood it rightly. We learned about the TPS, the Telescope Protection System, and how the many man-made satellites in the sky can cause too much RFI, Radio Frequency Interference, at times. There used to be a Multibeam Correlator, but it was no longer in its cupboard in the tower; it is kept in storage. The Dish is actually controlled remotely, these days, over the internet, so that people like George can observe from anywhere in the world, using this facility. Some of the pulsars George and his team observe are more than 15,000 light years away.

Brett shows us some astronomical calculations

Some of the work they do here is being funded by SETI, the Search for Extra Terrestrial Intelligence. They haven't found any yet.

The TPS, showing recent "alarm" events: high winds, etc.

Atomic Clock's display panel

The Apple logo is a jokey addition

Control room at the Parkes telescope

The steering machinery,
with heavy Dish above

The next part was quite exciting. Warning! said the notice. Authorised personnel only above this point. Hard hat protection required. Please let the operator know if you pass this point. We were about to climb the steps to the outside ledges. I told myself not to suffer from vertigo and went ahead, holding on to the railings tightly. There were great views from up there. As we edged round the ledge under the big dish, which is finely balanced, we squeezed past its surprisingly small steering motor. In the central core of the tower we were shown the Rotator, three concentric cylinders with slack cables that can move when the 'scope slews around on its pedestal. We saw a slight movement and heard a hum as the dish was automatically re-orientated. The pedestal has a solid shield with a gap at its base to compensate for expansion when it is warmed by the sun. Weight and balance factors are a challenge, said Brett. That's maybe an understatement.

Looking towards supplimentary receivers at Parkes

Chris climbing the ladders to the next ledge

George showing us Barnes Wallis' invention

The "most important bit", according to Chris, was "where we saw the machinery that did the tracking to compensate for the earth's rotation. This is naturally a big problem for such a large telescope. Brett showed us the solution, designed by Barnes Wallis of bouncing bomb fame, which consisted of a much smaller tracking system, a sophisticated version of the system used in amateur astronomy, which shone a laser onto a spot to which the large telescope then aligned itself, purely using the laser's beam." (I let Chris dictate those last few sentences because, although I think I followed the explanation, I failed to take notes at the time.)

Finally we descended inside the tower down the spiral, metal staircase and so back to normality. I bought some souvenirs in the gift shop where the shop assistant told me that they liked George's visits.