Satellite Laser Ranging

Satellite Laser Ranging (SLR) as its name suggests ranges (or measures distance) to Earth orbiting satellites using a powerful laser to detect a satellite's variation from its predicted orbit. It is uniquely suited to accurately determining the variation of the Earth's centre of mass, along with the orbit parameters of satellites orbiting the Earth.

Data from a global network of SLR stations are used to estimate the orbital parameters of satellites which revolve around the Earth's centre of mass. Therefore the position of the Earth's geocentre, the origin of the global reference frame, can be monitored through time.

SLR has become an important geodetic instrument to be used for the establishment of an accurate global geodetic infrastructure and Earth monitoring science.

SLR contributes to:

• the definition of the International Terrestrial Reference Frame (ITRF) by being the only space geodetic technique which defines the Earth's centre of mass. In addition, provides scale and the core network for the ITRF
• monitoring Earth rotation and polar motion to provide the relationship with The International Celestial Reference Frame (CRF)
• modelling the temporal and spatial variation of the Earth's gravity field
• determination of the Ocean and Earth tides
• monitoring tectonic plates and horizontal and vertical crustal deformation
• orbit determination for spaceborne altimeters and radar measurements for studies in global ocean circulation and changes in ice masses.

The Geoscience Australia Lunar and Satellite Laser Ranging program began in March 1973 with the signing of a NASA-Division of National Mapping agreement under the USA-Australia Hornig Treaty for cooperation in Science.

Satellite Ranging Observatories

Orroral Satellite Laser Ranging Observatory

The then Lunar Laser Ranging (LLR) facility at the Orroral Observatory located in the Namadgi National Park, 70 kilometres south of the Australian Capital Territory, was finally constructed and occupied in March 1975. During the period 1978-1980 LLR was the primary activity at the Orroral, which closed on 31 October 1998 and was replaced by a new facility located on Mount Stromlo.

Following a grant from NASA, the Orroral Observatory was upgraded to Satellite Laser Ranging (SLR) in 1981. In 1984, the first observations to the Lageos satellite were taken.

Mount Stromlo Satellite Laser Ranging Observatory

The Mount Stromlo Satellite Laser Ranging (SLR) facility is part of a worldwide network of approximately 42 SLR stations with only six located in the southern hemisphere. The Mount Stromlo facility is one of two SLR units managed by Geoscience Australia and currently operated under contract by Electro Optic Systems (EOS). The second facility is at MOBLAS 5 (Yarragadee), near Dongara, Western Australia.

The Mount Stromlo facility is newly built after being destroyed in the January 2003 bush fires that swept across two-thirds of the Australian Capital Territory (ACT). The official opening was on 1 April 2004, and after further testing and validating, became operational on 1 December 2004.

MOBLAS 5 Satellite Laser Ranging Station

The Moblas 5 (Yarragadee) SLR facility is located 100 kilometres south east of Geraldton, Western Australia. The observatory plays an important part in the Australian and International geodetic framework and has been operational since 1979. The observatory includes the University of Tasmania (UTAS) Very Long Baseline Interferometry (VLBI) radio telescope which was established as part of the AuScope Program. The observatory is adjacent to the Universal Space Networks (USN) facility. The Moblas 5 (Yarragadee) SLR facility is managed and operated by Geoscience Australia staff. NASA operates a number of Moblas facilities around the world and owns the MOBLAS 5 equipment.

At the Moblas 5 site there are also Global Navigation Satellite Systems receivers along with a DORIS transmitter and time reference equipment.