Future spacecraft might navigate by measuring pulsars. via
For the directionally-challenged among us, GPS is a life saver. A series of Earth-orbiting satellites can tell us where we are and how to get where we’re going with a pretty small margin of error. Yet GPS only works on Earth.
Spacecraft—or future astronauts—traveling to distant stars and planets won’t have such a sound navigational tool. There unfortunately isn’t a Galactic or Universal Positioning System in place. But scientists are close to developing one using pulsars and software.
The satellite network that gives up GPS on Earth is similar to how we track spacecraft out in space. Using a network of ground-based tracking stations, signals from the spacecraft are triangulated to pinpoint it’s location within a fairly small margin of error. But this system only really works when the spacecraft is going away from the Earth in a straight line, and it gets harder the further the spacecraft is. So tracking a spacecraft on a long trajectory through three-dimensional space is pretty tough.
What we need is a series of satellites or tracking stations spread throughout the universe equivalent to the GPS network we use on Earth. And rather than attempt to set one up, scientists are looking at using pulsars are the basis of this universal tracking network.
Pulsars are neutron stars. They rotate, and as they rotate they emit beams of radiation, and when that beam sweeps by and faces the Earth, we can measure it. From our Earthly perspective, the radiation pulses. Hence the name pulsar. It’s like seeing the light flashing from a lighthouse as it sweeps in circles off in the distance.
Pulsars rotate at varying speeds, some pulsing as often as once each millisecond. But what ever the pulse rate, some are extremely regular, and this is the key to using them as a universal GPS system. Pulsars are so reliably regular that a clock based on the signal from a pulsar would be more accurate than an atomic clock.
An artist's depiction of the planet orbiting a pulsar PSR B1257+12. via
With that level of accuracy, it could take as little as three pulsars to pinpoint a spacecraft’s location in space. A team of researchers at the Max Planck Institute in Germany says that by measuring the arrival time of signals from three or more pulsars and comparing that to the signal’s expected arrival time for a given location on Earth, they can pinpoint a spacecraft’s location to within three miles. The biggest challenge, they say, is that signals from pulsars are generally very long wavelength so need a large and expensive antenna, but it’s doable.
A team of scientists led by Dr. George Hobbs of CSIRO—Commonwealth Scientific and Industrial Research Organisation, Australia's national science agency—is taking pulsar-based GPS a step further. They’ve figured out a software program that will use information from pulsars to guide spacecraft.
Hobbs and his colleagues study pulsars, typically measuring the exact time pulsar pulses reach the Solar System and looking for deviations; any change hints at the pulsar’s properties, like whether it’s orbiting another star. But Hobbs, whose team measures pulsars using telescopes, says they can work backwards to use the pulsar information to pinpoint the location of their telescopes. If the telescope observing the pulsar were on a spacecraft, the signal could be used to pinpoint the spacecraft’s location anywhere in space. A software program would make it so the spacecraft could use this pulsar information to autonomously guide itself through the universe.
This autonavigation system isn’t incredibly important for the short missions like to our nearby planets, but any spacecraft venturing beyond the Solar System would benefit from this method. The telescope on a spacecraft, likely a lightweight X-ray telescope, would use pulsars whose rate and intensity is well known by Earth-based observations.
Early versions of Hobbs’s software, called TEMPO2, has simulated a spacecraft navigating itself to Mars; the fake mission arrived with incredible accuracy. His team has also used the software to measure masses of objects in the Solar System, and to rule out unseen masses like the notorious undiscovered planet Nibiru (it’s not there).
Scientists have been interested in pulsar navigation since the mid-1970s. So maybe in another 30 or 40 years we’ll see spacecraft with lightweight X-ray detectors taking themselves around the Solar System.