Is it feasible to use dead stars to navigate spacecraft in deep space? Long-term space travel may be a pipe dream outside science fiction math but people inside science are at least thinking about how to make navigation possible. 

Spacecraft navigation currently relies on radio transmissions between the craft and a network of ground-stations on Earth. This means that the craft has to wait for an instruction from Earth to guide it through space and with the large distances involved this could take hours, days or even longer - not really practical if we are going to Alpha Centauri. Even for unmanned ships going to closer areas, that time delay affects a spacecraft's ability to react rapidly according to its location, and ground infrastructure becomes increasingly difficult and expensive to maintain due to the size of radio antennas.

That traditional form of ground-based space navigation is also limited in the number of spacecraft it can manage, as only one set of measurements can be processed at any one time. If feasible, a new pulsar technique could allow a greater number of complex space missions to take place simultaneously in deep space, because spaceships become capable of navigating themselves. 

Researchers at  the National Physical Laboratory (NPL) and the University of Leicester are exploring the use of X-rays from pulsars - dead stars - to allow spacecraft to navigate without phoning home for directions. Pulsars are highly compact and rapidly rotating neutron stars that emit intense electromagnetic radiation observed as pulses, similar to the rotating beam of light seen from a light house. In some cases these pulses can be highly regular, making them suitable sources for navigation using a technique similar to GPS.

"Using on-board X-ray detectors, spacecraft could measure the times of pulses received from pulsars to determine the position and motion of the craft. The University of Leicester will use their experience in X-ray astronomy to come-up with potential designs of the device and NPL will develop timing and navigation algorithms to determine the potential accuracy of this technique. Funding received from ESA will allow us to investigate the feasibility of using these dead stars and the potential navigation performance that could be derived." says Setnam Shemar, leading the project on behalf of NPL's Time and Frequency Team.

Results from the investigation will advise ESA on technical strategy and if successful, pulsar navigation could in the long-term reduce costs and limitations associated with ground-based technology. Such a method, using pulsars as nature's own GPS in space, might one day enable humanity to navigate far beyond the outer reaches of our Solar System.