The Dish at Parkes celebrates 50 years
- 31 October, 2011 11:11
The Parkes Radio telescope. Image credit – David McClenaghan, CSIRO.
It is rare for a piece of scientific equipment to hold a place in a nation’s heart. But ‘The Dish’ — the CSIRO's Parkes radio telescope — has in come to come to mean a lot more to Australians that just a complex piece of technology. Today, it celebrates its 50th anniversary.
The telescope is a 64-metre diameter parabolic dish used for radio astronomy, located about 20 kilometres north of the town of Parkes, New South Wales — about 380 kilometres west of Sydney. Opened on 31 October 1961, the telescope is perhaps best known to Australians for its role in the 1969 moon landing.
The Parkes telescope was originally planned as a backup during the moonwalk for NASA's two tracking stations, the 64 metre dish at Goldstone in California, and the 26 metre dish at Tidbinbilla near Canberra, Australia. The idea was that the 26 metre dish at Honeysuckle Creek tracking station, near Canberra in Australia, would track the command module, Columbia, and co-ordinate the effort between the Australian stations, with the Goldstone dish acting as the prime receiving station.
According to the original flight plan, the astronauts would undertake the moonwalk, or extra vehicular activity (EVA) shortly after landing; it would be all over by the time the Moon was due to rise at Parkes — 1:02 pm Australian Eastern Standard time (AEST). The plan was for the astronauts to deploy a three metre, erectable, S-band antenna (this was done later on Apollo 12 and 14) to provide greater signal strength from the Moon.
But as with the best laid plans, things changed. In May 1969 the mission plan was altered to allow a rest period before commencing the lunar EVA. The idea was to give the Apollo 11 team a break and adjust to the difference in gravity. Instead the EVA would occur at 4:21 pm AEST, when the Moon was high overhead at Parkes.
All of a sudden, ‘The Dish’ became the prime receiving station.
Neil Armstrong, however, decided on an immediate moonwalk — five hours before the Moon was to rise at Parkes. It made sense; it would be hard to rest with all the excitement of the first ever moon landing. For moments, it seemed the moonwalk would be over before the Moon even rose at Parkes and Goldstone again assumed the role as the prime tracking station.
But it took time for the astronauts to put on the portable life support systems, boots, gloves and equipment, and it also took longer than expected to depressurise the cabin of the lunar module.
The project was not without its dramas; on the day of the Moonwalk the wind was gusting at 100 km per hour. Normally the telescope would not operate under such conditions due to safety reasons, but the telescope director gave the go-ahead. Wind gust in excess of 110 kilometres per hour (70 mph) buffeted the telescope, subjecting it to forces 10 times stronger than what was considered safe operating limits.
‘The Dish’ was tipped to its limit, waiting for the Moon to rise and ready to receive the television pictures, thanks to the ingenuity and quick-thinking of NASA’s John Bolton and the team. And the Parkes radio telescope took its place in history.
‘The Dish’ is operated by CSIRO Astronomy and Space Science (CASS), a business unit of CSIRO. CASS also operates the Australia Telescope Compact Array near Narrabri, NSW, and the Mopra radio telescope near Coonabarabran, NSW, and is developing the Australian SKA Pathfinder (ASKAP) telescope in Western Australia.
Built in 1961, the telescope’s basic structure is unchanged, but most other aspects such as the surface, control system, focus cabin, receivers, computers and cabling have been upgraded — in some cases many times — in line with advances in technology. According to the CSIRO, the telescope is now 10,000 times more sensitive than when commissioned.
It even has its place on the Big Screen, immortalised (if an inanimate object can be so described) in the 2000 movie, The Dish.
It is also part of an ongoing program, called PULSE@Parkes, that gives students around the country the chance to undertake science with a large, professional, radio telescope.
Operation of ‘The Dish’
The telescope operates 24 hours per day, through rain and cloud. About 85 per cent of all time each year is scheduled for observing. It must close down during times of high wind — the moving part of the dish sits on top of the tower and the large surface area means the telescope must be 'stowed' when the wind exceeds 35 kilometres an hour.
Regardless, less than 5 per cent of that is lost because of wind or equipment problems.
About 300 researchers use the telescope each year, and more than 40 per cent of these users are from overseas.
- Diameter of dish: 64 m
- Collecting area of dish: 3216 m2
- Height to top of focus cabin: 58 m
- Focal length: 27.4 m
- Weight of dish: 300 tonnes
- Weight above control tower: 1000 tonnes
- Maximum tilt: 60° from the vertical
- Time to maximum tilt: 5 minutes
- Time for 360° rotation: 15 minutes
- Surface accuracy: 1–2 mm difference from best-fit parabola
- Pointing accuracy: 11 arcseconds rms in wind (about the width of a finger seen 150 m away)
- Maximum operating wind speed: 35 km per hour
- Motors: 4 x 15 hp 480 volt DC
- Gear ratios – 40,000 : 1
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