By Irena Guettel
Big Brother will soon be watching the high seas, thanks to a new satellite with a 4-metre antenna designed to track maritime shipping across the globe. “We describe it basically as a flying antenna,” says Tom Sproewitz, engineer at the German Aerospace Centre DLR in the northern port city of Bremen. Sproewitz is easily able to hold the giant helix with two fingers, as it is ultra-light despite its size, an essential property for an antenna that must be sent aloft to significantly improve shipping tracking. AISat is Germany’s first satellite to track worldwide shipping movements.
It will use an existing system, the automatic identification signals (AIS) which are mandatory in maritime traffic to prevent ship collisions. The signals use VHF frequencies and have a range of about 20 nautical miles on the surface. Using satellites to pick up the signals can be problematic, especially in busy shipping lanes. “There are so many ships equipped with AIS en route in the North Sea that the signals overlap and are no longer distinguishable,” explains Ralf-Dieter Preuss from the German Maritime Agency in Hamburg. This is because most standard satellites are equipped with non-directional copper antennas, which cover an area with a diameter of 6,000 kilometres. In contrast, the satellite developed in Bremen will be much more precise, thanks to the use of a high-gain helix antenna.
“It reduces the footprint to a diameter of 750 kilometres,” says DLR project director Joerg Behrens, who has worked with his colleagues on the 1-million-euro ($1.3-million) development for the past four years. To date, helix antennas have only been used on espionage satellites, but on a much smaller scale than the antenna built in Bremen, which needed to be both light and stable. “It is unique because of its size and application,” says Behrens. “It was a real challenge to build this antenna.” Scientists tested different materials in zero gravity before deciding on a reinforced carbon-fibre plastic with a copper casing. The antenna weighs just 800 grams while the entire satellite comes in at only 13 kilograms.
The DLR is running final tests and hopes that AISat will be complete by June. The satellite will then be launched into space at the end of this year or in early 2014 on an Indian rocket. The satellite will orbit at a height of 650 kilometres, undergoing tests for several months and transmitting data to two ground stations ‚Äî one in Bremen and the other in northern Canada. Scientists have set ambitious targets for the AISat satellite tracking project, which importantly include the observation of possible terrorist boats, detection of vessels hijacked by pirates or to expose environmental polluters at sea.
The International Maritime Organisation (IMO) established the long-range identification and tracking (LRIT) of ships as an international system in 2006, whereby ships have to log their positions every six hours with a worldwide database network. International research is continuing into how this system can be replaced by AIS. “It would be cheaper and the information would be available in real time,” says Preuss. Researchers in Bremen will only learn over the coming year when their satellite is in orbit whether AISat is a possible suitable replacement. ‚Äî DPA