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  Mini sats to improve Earth observation
A constellation of miniature satellites working as a group could better monitor disasters, map the planet and help improve climate predictions, says an Australian engineer.

Dr Xiaofeng Wu of the University of Sydney has developed a control system for such satellites and presented his research at the 9th Australian Space Sciences Conference in Sydney.

Wu's control system that predicts the trajectory of a satellite's nearest neighbours and communicates this prediction via a wireless network and on-board computer.

The satellites, which are still at the development stage, will measure 10 centimetres cubed and fly up to 22 kilometres apart. Each will communicate via a 'protocol' similar to wireless networks, or WiFi, and use a predictive model to compensate for any delay in receiving signals.

"In communicating with each other to find out the neighbouring satellite's attitude and position, there is a delay and information packet loss in wireless communications," says Wu.
Constant communication

"To address this, the control system on board each satellite predicts each [other's] attitude and calculates this on board, then compares it to the actual satellite attitude. The information is used to adjust the controls on board the satellite."

The satellites need to consider other satellite's attitudes in a continual loop in order to achieve their performance, he says.

So far, Wu has built hardware for attitude determination and control. He also has the satellite structure and on board computers, as well as the communication protocol for inter-satellite communication.

He is working with the colleagues in the UK to develop the virtual space sensor architecture and is seeking funding from the Australian space sciences research program.
Better coverage

When built, the satellites could be deployed into a low Earth orbit equipped with sensors.

"You can cover a much wider area than you can with terrestrial [sensors] and transmit signals to ground stations at almost real time," says Wu.

Miniature satellite networks could be used for surveillance and reconnaissance, humanitarian and disaster assistance, collecting weather and ocean data and monitoring forest fires.

Professor John Le Marshall, senior scientist in charge of future satellites systems for the Bureau of Meteorology in Melbourne says the system would be a useful way of deploying instruments.

He says it is a logical extension of satellite systems such as NASA's A-Train satellite constellation, a line of six satellites that follow each other in orbit around the Earth.

"Instead of putting all the satellites on the same flight like Battlestar Galactica, if you put them in a constellation you reduce the risk that you have the same observations of the same area at the same time," he says.
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