Aussat In Profile

In technical terms, the purpose of Aussat is to finance and launch two multi-transponder satellites to operate uplink in the 14 to 14. 5 GHz frequency band, and downlink in the 12. 25 to 12. 75 GHz band. The frequencies are extremely high, and the wavelengths are minutely small. There will be a total of 4 x 30 watt transponders and 11 x 12-watt transponders. The satellites will be launched between July and September 1985.

Each satellite is expected to remain in serviceable condition for at least seven years from that date.

The Codan Organisation and NEC Australia have contracted to supply receiving equipment for consideration by the Department of Communications for the general reception of direct broadcasts from the satellites.

The Aussats will be supplied by Hughes Aircraft, and in keeping with the Australian Government’s policy of requiring offsets for our local industries, AWA has been awarded a five million dollar slice of the action for the design and production of two ground stations for satellite-tracking and monitoring. In actual fact, Hughes Aircraft is building three satellites. One will remain firmly on the ground as a standby, while the other two fly.

The Minister for Defence Support, Mr Ian Viner, said recently that the offsets to AWA ‘are the first awarded by Hughes against its commitment to involve Australian industry in the satellite project. ‘

The Department of Aviation has reserved the exclusive use of between two and four of the satellite transponders, to introduce vastly improved VHF communications facilities between aircraft and ground stations. At the present time in Australia, there are three main types of radio transmissions used by aircraft. That is, HF, VHF and UHF. The HF is used for long-range overwater or overland communications, where line-of-sight VHF and UFH signals cannot penetrate. Much of Australia’s aeronautical radio traffic is on domestic or international HF. These are shortwave frequencies. Short-range communications, particularly near cities, is on VHF for civil, and UFH for military aircraft. The exception to this rule is where VHF repeater stations have been installed to receive a signal at a distant location just inside VHF range and re-transmit it to another far-off station, well outside the normal VHF range. If one of these VHF repeaters becomes unserviceable, aircraft using it are usually advised to contact a HF ground station. The long-range VHF is directly manned by an air traffic controller, whereas the HF is manned by a flight service officer. If the aircraft has radio troubles using the VHF and has to be directed to HF, he is taken away from the direct supervision of an ATC man and has to communicate with a flight service officer, who relays requests from the ATC personnel.

With Aussat in use, all this would be different. If a VHF channel became UIS, another channel would simply be selected. If an entire satellite packed up, and that is extremely unlikely during the satellite lifespan, the second satellite would be operational, and communications would be shifted to that vehicle.

About 250 ground stations will, by linking with the satellites, be able to speak to aircraft, on VHF, Australia-wide. Each of the 250 ground stations will be provided with two satellite ground stations. One will be operational, the other a secondary or backup.

The task of organising a domestic communications satellite is a mammoth one. However, the Aussat staff appear to be coping well with their brief.

The frequency band of 12 to 14 GHz was specially selected by arrangement with Telecom Australia, so as not to interfere with Telecom’s ground-based microwave equipment.

The Aussat arrangement will be for a single antenna to provide coverage for the entire Australian continent. That includes offshore islands. The remaining antennas will be used to provide coverage on a spot-beam basis to New Guinea and Australia. Aussat has already paid out 10,000 dollars for the projected launches.

Weighing in at 655 kg, the Aussat modules will be 2. 2 metres in diameter, extending to 6. 6 metres when a lower-skirt antenna is positioned.

Example of Improvement to VHF service by Aussat

Take a typical, daily Qantas service. Qantas flight OF 1 for example. This aircraft leaves Sydney with its first touchdown point being Singapore. The route can be via Darwin or Derby. If we look at the Derby track, OF 1 will overfly waypoints Katoomba, Parkes, Reola, Kalug, Alice Springs, Turli, Derby. . . and then it goes oceanic.

At present, VHF repeater links end at position Reola, in far northern NSW. At Reola, OF 1 calls up Sydney on HF until it reaches Kalug, and than at Kalug VHF communication is possible with Alice Springs. VHF is maintained to Turli, through repeaters, then at Turli, HF radio is used again with Darwin. It’s a bits-and-pieces system, requiring several changes of radio equipment during the Australian overland journey by OF 1.

With Aussat, this will change, for the better.

Sydney VHF coverage will extend from Sydney to Reola, as it does now, but without the need for repeaters. At Reola, VHF coverage will begin with Alice Springs, and through to Turli. VHF coverage from Turli to Derby, and beyond there, will be with Darwin. Shipping and Railway usage of Aussat is also being seriously examined at the present time.

If the Aussat programme wasn’t implemented, and the satellites were not launched, DoA would have to extend the facilities for HF communications.

But Aussat will become a reality in 1985-86, and the use of HF can be minimised. There will be an HF service maintained for domestic use for aircraft that are below VHF coverage, and of course, all long-range oceanic traffic will continue to operate on the HF/SSB frequency families.

In the future, DoA has visions of direct aircraft-satellite working, eliminating the costly ground stations. And in the long term, I can personally see the day when a worldwide network of orbiting satellites flying above pre-determined locations on the globe will enable VHF-ATC coverage over the oceans of the world.

HF radio is affected by solar storms and other atmospherics. Its principle lies in bouncing space-bound radio waves back to Earth off the ionospheric layers and returning the signals to Earth for reception vast distances away from the originating station. HF is crackly, noisy and prone to fading without warning. Frequencies must be selected accordingly, with time of day, month and year taken into account, while outside influences such as solar storms, which create sunspots and disrupt certain frequencies have to be borne in mind.

Aussat will terminate this unreliability.

The two Aussat satellites will be separated from each other by 8 degrees of longitude. The first will be positioned at 156 degrees East, and the other at 164 degrees East. Each earthbase will have two stations aimed at each of the satellites. The two ground stations will have to be located apart, as rain will affect signals if they are located together. When any one of the satellites looks like failing, a third satellite will be placed in orbit between the two existing satellites, and then will be moved in to replace the ailing satellite when required.

The frequency bands chosen for the satellites, as stated earlier, are not the traditional satellite bands of 4 to 6 GHz. This has been a purposeful decision so as not to interfere with other SHF, or ‘super-high-frequency’ stations. Cost of operating the satellites is believed to be about 6. 5 million dollars per annum, with four million dollars of that cost being transponder-rental.

And for that cost, we in Australia will have a communications system that will be second to none of those in use worldwide.

Through AUSSAT!