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RSAA News of the Month: May 2003

Stromlo Gravity Instrument Survives Firestorm
Despite the firestorm, one instrument kept right on recording

 

When flames of up to 1200 degrees Celsius destroyed much of Mount Stromlo Observatory, including five telescopes, the Old Administration Building, workshops and seven houses, Australian science suffered a serious blow. But in a rarely-visited corner, behind the fire doors of the 60's era computer room in the basement of the Old Administration Building, Australia's most sensitive gravity meter was protected from the worst of the onslaught.

Fire damage in the basement of the Old Administration Building. This area was the Solar Physics Laboratory of the Commonwealth Solar Observatory. The arched structure is the bottom of the heliostat tower. The concrete pillar in the centre of the arches held a flat mirror at 45 degrees; the mirror was rotated to send the heliostat beam to the required one of four instruments mounted in adjoining rooms. As part of the conversion to a computer room, the tower structure was hidden behind wooden walls in the early 1960s.

The Superconducting Gravity Meter (SG) relies on the exotic properties of metals at extremely low temperatures to detect faint changes in gravity hundreds of times more sensitively than conventional gravity survey instruments and is used to detect movements deep in the interior of the Earth. It is owned by the National Astronomical Observatory of Japan and operated for them by the Australian National University's Research School of Earth Sciences.

With its support equipment outside destroyed and power lost for over a month, its operators struggled to keep the superconducting core of the system at 4.2 degrees above absolute zero by regular transfusions of liquid helium. This month, with the restoration of power and the refurbishment of smoke damaged electronics, came the news that the struggle has been worthwhile.

Continuity is everything for this experiment, which has been running continuously for the past 6 years, give or take a few blackouts. When the electronic systems and recorders were all reattached, the output record at first oscillated wildly but slowly steadied to reveal its familiar signals. This meant that the ping-pong ball sized sensor inside the unit had remained levitated in its magnetic cradle throughout the fire and its aftermath, and was now back in action.

The end and the new beginning. the chart record shows the last hours of the system on the day of the fire and the revival of the system eight weeks later. Browning of the chart paper on Jan 18 is caused by the fire.

Representatives of the Observatory, the Research School of Earth Sciences of the ANU and the National Astronomical Observatory of Japan were on hand to witness the revival of the instrument, marking another step in the recovery of the Observatory.

There are still some difficult times ahead. The process of rebuilding Stromlo will produce a lot of noise, which is not the ideal background for an instrument used to the normally quiet environment on the mountain. With time, however, it can look forward to retaking its place in the worldwide array of similar devices listening to the heartbeats of the Earth.

Greeting the recovery of the SG (from left) Dr Herb McQueen and Professor Kurt Lambeck of the Research School of Earth Sciences, Professor Seiji Manabe of the National Astronomical Observatory of Japan (NAO), Professor Penny Sackett, Director of the Research School of Astronomy and Astrophysics, and Professor Tadahiro Sato of NAO.

Contact: Herb McQueen, Research School of Earth Sciences, ANU

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