Dead stars to guide spacecraft

German scientists are developing a technique that allows for very precise positioning anywhere in space by picking up X-ray signals from pulsars.
These dense, burnt-out stars rotate rapidly, sweeping their emission across the cosmos at rates that are so stable they rival atomic clock performance.
This timing property is perfect for interstellar navigation, says the team.
If a spacecraft carried the means to detect the pulses, it could compare their arrival times with those predicted at a reference location. This would enable the craft to determine its position to an accuracy of just five kilometres anywhere in the galaxy.
"The principle is so simple that it will definitely have applications," said Prof Werner Becker from the Max-Planck Institute for Extraterrestrial Physics in Garching.
"These pulsars are everywhere in the Universe and their flashing is so predictable that it makes such an approach really straightforward," he told BBC News.
Prof Becker has been describing his team’s research here at the UK National Astronomy Meeting in Manchester.
The proposed technique is very similar to that employed in the popular Global Positioning System, which broadcasts timing signals to the user from a constellation of satellites in orbit.
But GPS only works on, or just above, the Earth so it has no use beyond our planet.
Currently, mission controllers wanting to work out the position of their spacecraft deep in the Solar System will study the differences in time radio communications take to travel to and from the satellite. It is a complex process and requires several antennas dotted across the Earth.
It is also a technique that is far from precise, and the errors increase the further away the probe moves.
For the most distant spacecraft still in operation – Nasa’s Voyager satellites, which are now approaching the very edge of the Solar System, some 18 billion km away – the errors associated with their positions are on the order of several hundred km.