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Partnering with the US to test a world without GPS

24 August 2016
The team prepare for a GPS-free UAS flight trial at Woomera.
The team prepare for a GPS-free UAS flight trial at Woomera.

Defence researcher Sam Dudley, works with unmanned aerial systems (UAS), specifically trying to optimise and improve the performance of a datalink between a far-off UAS and home base.

Dudley’s work is conducted under a Project Agreement with the US Air Force Research Laboratory (AFRL).

“Our aim under this project is to navigate a UAS aircraft without GPS assistance to a target location 100 km away,” Dudley explains.

“As part of that, to maintain range safety and for operational reasons, we need to maintain communications with the aircraft over the 100 km outward journey.”

“My work has really been examining the data link for that system and trying to keep it as reliable as possible while minimising the amount of infrastructure and complexity.”

Dudley and the team use the Woomera Test Range in the South Australian desert for these trials. The entire unmanned aerial mission must be conducted from a single launch and recovery location, to minimise the number of personnel required and to reduce infrastructure.

The team chose a flight altitude of 450 metres above ground to optimise safety in case of a system failure and the opportunity to capture high quality data for the on-board experimental systems.

 “Reliable datalink communications are paramount to the success of our extended-range flight trials, but the trade-off we made in flying at 450 metres is less-than-optimal for radio communication,” said Dudley.

“My paper at last year’s International Aerospace Congress presented some solutions to this problem.”

Standard testing was insufficient in predicting the performance of the datalink, as reflections from the landscape at such altitudes causes significant destructive interference in otherwise clear line-of-sight conditions. Through modelling, Dudley has shown it is possible to exploit these effects in order to minimise the impact on the datalink operations.

“I presented an experimentally demonstrated solution in the paper,” he said.

With the datalink well on the way to being stable, the team is able to pursue its key project research focus, namely passive navigation.

“That means using available emitters, whether it be light or some other radiation source or even the polarisation of the sky to guide our UAS. In many ways we take inspiration from biology, for example migrating birds, or insects finding their way back to the hive,” says Dudley.

An AFRL contingent joined Dudley and colleagues at Woomera earlier this year for a successful trial, one of many such trials that have taken place.

He believes the US defence scientists appreciate the research flexibility available at the Woomera range, and also the flexible nature of the DST auto-pilot software.