Space is big — really big. And if you want to successfully navigate the interstellar depths of our Milky Way galaxy, you’re going to need some sort of reliable system. A new proposal tries to keep the method as simple as possible: use pairs of stars to provide a galactic reference frame.
Within our solar system, interplanetary spacecraft rely on Earth-based systems for navigation. When we send a radio signal to a spacecraft and it replies, we can use the time delay of the reply to calculate a distance. We can also monitor the spacecraft in the sky, and by combining all that information (position in the sky and distance from Earth), we can pinpoint the spacecraft’s location in the solar system and provide that information to the spacecraft itself.
We can also use the Doppler shift of those radio waves to estimate the speed at which the spacecraft is moving away from Earth. By using dishes scattered across our planet, we can measure the delay from a spacecraft’s signal reaching one dish versus another. When we combine that data with the position information, we have a complete six-dimensional lock on the spacecraft: its three dimensions of position and its three dimensions of velocity.