Last updated 12Jun23
The Orroral Geodetic Observatory is located on the ridge high above the Orroral Valley and under Mt Orroral in the Namadgi National Park.
Location: GR 55H FA 75592-54664 (MGA94), Rendezvous Creek 8626-1S 1:25000
• Plaque at Observatory: This domed circular building was built in 1974 as part of the USA-Australia Hornig treaty for co-operation in science. NATMAP (now AUSLIG) and NASA were the signatories. A 10 ton telescope and laser from Arizona, USA were installed in the building for the purpose of Lunar Laser Ranging whereby laser pulses fired to the moon are bounced back again via retroreflector mirrors placed on the moon’s surface by Apollo astronauts. The measurements of the time of flight yield information on the motion of the moon, the rotational wobbles of the earth, continental drift and the theory of relativity. Further improvements in 1981 enabled the facility to track artificial satellites. This became its primary function. More detailed studies of the earth’s gravity field, tides, glaciers and El Nino phenomenon became possible. The Observatory also hosted GPS receivers and a DORIS transmitter, to make it Australia’s fundamental survey station. Additionally 4 atomic clocks here at Orroral provided Australia with its official time. In 1997 it was decided to close the Orroral facility and move its functions to a newly built, fully automated facility at Mt Stromlo, ACT. Tracking ceased in November 1998. Only the original Observatory building now remains as a reminder of Orroral’s 25 year contribution to the space industry. This plaque is dedicated to the hardy men and women who worked here between 1974 and 1998.
• A wonderful contribution from Matthew Higgins, local eco-historian and author. Check out this article for background on the geodetic observatory.
• Another historical article, the ACT heritage Council’s background paper for registration of the site. Thanks to the BBC Jul-Dec 18 Walks Program for taking me to this article.