ScienceWise - Winter 2011

Antarctic broadband

Improving communications in the last great wilderness

The Antarctic is the last great uninhabited wilderness on Earth and has long held a fascination for humans inspiring early explorers to struggle and frequently die in search of its hidden secrets. Even today with our modern technology, it’s a dangerous and inhospitable place. However, today the drive to do science in the Antarctic is motivated not so much by pure curiosity as by the vital information about the Earth’s past, present and future climate that can be gleaned there. Increasing numbers of Antarctic scientists using ever more sophisticated equipment are generating more and more data on the frozen continent and this is beginning to create a problem.

As things stand communications in the Antarctic are patchy and insufficient for the needs of the research community. There isn’t anywhere close to sufficient volume of traffic to induce traditional satellite communications companies to actively cover the Southern tip of the planet so any satellite access there is often very near the horizon and sporadic due to orbital constraints and weather.

However, the Antarctic Broadband consortium – comprising a number of universities and private companies – is aiming to change all that. Their proposal is to launch a constellation of small satellites in a highly-elliptical orbits with a high-bandwidth communications payload specifically design for the needs of Antarctic users.

A continuous coverage geosynchronous orbit such as those used by communications and TV satellites isn’t an ideal solution at the pole because to stay over the same point on the Earth, it must have an orbit over the equator. Some Antarctic stations can access geosynchronous satellites, but the quality and capacity of the service is challenging. To get around this, the Antarctic Broadband satellites would be placed in a highly elliptical orbit with the apogee over the southern pole – similar to what’s known as Molniya orbit.

These highly elliptical orbits have a unique property such that, according to Kepler’s law of equal areas, the satellite moves across the sky slowly whilst on one side of the Earth and very quickly at the other. It’s a clever way of keeping a satellite over one place for most of the time without having to have it above the equator and has been used for Russian communications satellites for many years. The plan is to have two or more satellites orbiting out of phase so that there is constant coverage on the Antarctic continent.

To keep size and weight down and communications capacity high, the consortium plans to us use Ka-band (26.5-40 GHz ) radio communication and highly directional transmitting and receiving antennae on the spacecraft. This would necessitate a complex attitude control system on board each spacecraft in order to keep the antennae pointed at the Antarctic circle and internet gateways back on the other continents as the satellite sweeps across the sky.

The first launch in this plan will be a technology and capability demonstrator mission using a nano-satellite - an industry term for a satellite that is a few tens of centimetres across which is very small by satellite standards.

The primary command and control ground station for both the demonstrator and operational satellites is has recently been commissioned at the ANU Research School of Astronomy and Astrophysics, one of the partners in the consortium. This ground station will be used to download test data and upload control instructions to the spacecraft as they fly over Canberra.

Mike Petkovic is a project manager currently working on the Antarctic Broadband project “We’re just completing phase one of the project,” he says, “Which is essentially demonstrating that our technology works. We can upload telemetry information to and download data from satellites already in orbit which are of course the two fundamentals in this game. We’re looking forward to working with our own satellites in the near future.”

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