At the American Astronomical Society’s 231st meeting, in Washington, D.C. earlier this month, Keith Gendreau, principal investigator for NASA’s Neutron-star Interior Composition Explorer (NICER) mission described something remarkable: the first successful demonstration of a system to use pulsars for navigation in space.
The basic idea is similar to what is done with the Global Positioning System (GPS) or other global satellite navigation systems. When you use GPS to find your way to Starbucks, you are depending on transmissions from an array of satellites whose positions are precisely known. The timing of the signals you measure can thus be used to deduce the position of the receiver. That works only if the receiver is on Earth or near Earth, however. If you wanted to visit a Starbucks in deep space, you have to find it by some other means.
Right now, deep-space navigation mostly depends on using radio signals sent from Earth to the distant space probe—signals that must be sent with giant antennas. The probe responds by sending a signal back. So it’s not hard to figure out range—overall distance—with good precision from how long a signal traveling at the speed of light takes to get to the probe and back. But angles are tougher to nail down. As a result, such position fixes degrade as you move away from Earth. Indeed, for critical operations, like insertion into orbit at the distances beyond Jupiter, space navigation done this way is especially challenging.
How then can spacecraft traveling far from Earth navigate precisely through the heavens? One possibility is to use pulsars as natural GPS beacons of a sort. To understand how that would work, though, you first need to know a little something about pulsars.