If you want to know where you are in space, you'd better bring along a map. But it's a little more complicated than riding shotgun on a family road trip.

Spacecraft navigation beyond Earth orbit is usually carried out by mission control. A series of radio communication arrays across the planet, known as the Deep Space Network, allows operators to check in with space probes and update their navigational status. The system works, but it could be better. What if a spacecraft could autonomously determine its position, without needing to phone home? That's been a dream of aerospace engineers for a long time, and it's getting close to fruition.

Pulsars are the key.

Pulsars are rotating neutron stars—the ultra-dense cores of exploded supergiant stars—which emit jets of electromagnetic radiation from their poles. They act like interstellar lighthouses that repeatedly wash radio signals over Earth in a dependable rhythm. The first pulsar was discovered by Jocelyn Bell in 1967 and was nicknamed LGM-1 (Little Green Men 1), because until a second one was discovered, extraterrestrial intelligence couldn't be ruled out as the pulsar's cause.