Heavenly body – the ADF in Space

“Secure and reliable satellite communications will be available to deployed forces, operational command and Australian headquarters,” Defence Minister Brendan Nelson said. “The WGS constellation of six satellites will provide a world class capability in terms of global coverage, operational flexibility and bandwidth. It will support multiple simultaneous high-tempo operations and provide a high level of redundancy. ” The new satellite will eventually replace the commercial Singtel Optus C1 satellite upon which the ADF currently relies for the bulk of its military communications.

Increasing concern in recent years over the sovereignty aspects of ‘piggy backing’ off foreign owned commercial satellites for military communications is believed to have led to the decision to go with the sixth WGS option.

The WGS satellite is based on a commercially- derived Boeing 702 airframe or ‘bus’, upon which a transponded, cross-banded-X and Ka-band communications suite, eight X-band phased array antennas, 10 Ka-band gimballed dish antennas, and one X-band Earth coverage antenna are mounted. The complete satellite weighs about 6000kg at launch including its highly corrosive xenon ion fuel which is added just before launch. When fully extended, a 702’s antenna ‘wing span’ is about the same as a 767 airliner.

The communications suite provides 4. 875 GHz of instantaneous switchable bandwidth, about 10 times that of the Defense Satellite Communications System III (DSCS III) system it will eventually replace, and will be capable of downlinking 2. 4 GBits of data per second to tactical users.

Although the US WGS program ran more than three years late and more than a third over budget by the time the first ‘bird’ was launched, much of this can be attributed to Congressional delays in approving funding for satellites three to five, approval for which was given in November 2006 and April 2007 respectively.

The satellite itself is just one of three segments of the WGS system, comprising the space segment, the terminal segment, and the control segment.

While the satellite comprises the space segment, the terminal segment describes the end ‘users’ or ‘customers’ of the communications services provided by the WGS.

In an Australian context, users will include Army ground mobile terminals, Navy submarines and surface vessels, RAAF Wedgetail AEW&C and AP-3C Orion surveillance aircraft, national command authorities, as well as various other national security agencies such as Customs and the AFP, and allied national forces.

The WGS Control Segment will be the physical ground based hardware and its human operators which will command and monitor the satellite and its communications payload, and are likely to be located to the new Joint Operations Command (JOC) centre near Canberra.

Boeing 702 satellites typically have a service life of between 12 and 20 years, a timeframe which is determined by how judiciously its finite fuel is used to position it in orbit. While the satellite itself costs about $325 million, to this must be added the launch costs, the extensive ground based communications segment, and any additional interfaces to existing equipment which may be required. The WGS has been designed to be largely interoperable with existing and proposed US, and by default, Australian X- and Ka-band terminals, and will have the largest capacity of any US defence communications satellite.

WGS will augment existing US X-band communications provided by the DSCS III and the one-way Ka‑band service provided by the Global Broadcast Service (GBS), as well as add a new two-way Ka-band service.

Twenty-two Boeing 702s were in service or on order at time of writing, and the bus has proved to be very reliable in service since first launch in 2006.

The first WGS satellite was launched in October aboard an Atlas V vehicle from Cape Canaveral, and the second was due to be launched in late November or early December, this time aboard a Delta IV also from Cape Canaveral.

The remaining four will be launched by either Atlas V or Delta IV in 2008, 2009, 2011 and the last, Australia’s ‘bird’, in 2013.