The future of space exploration lies in covering vast distances very quickly - with current spacecraft speeds it took the New Horizons mission about 9.5 years to complete a flyby of Pluto, approximately 32 Astronomical Units from Earth. Alpha Centauri, the nearest star system to our Sun, is approximately 276,395 Astronomical Units from Earth. In order to cover such a distance in a lifetime, a spacecraft will need to be traveling at a high enough speed that it would encounter relativistic effects, such as time dilation, length contraction, and Doppler shift. Current navigation systems do not take these effects into account.
These relativistic effects not only need to be accounted for when developing a high-speed navigation system, but can actually be used to navigate! For example: say that there is a spacecraft sitting at some point in the universe, imaging the stars. If we have some idea what the stars are supposed to look like at the spacecraft's location, we can pinpoint where it is using the imaging data from the spacecraft. Accurate high-speed distance navigation relies on solving two problems:
One, even though we know very well what the stars look like from Earth, the same is not true for stars from the other side of the Milky Way, for example. A robust navigation system would need to use data taken while traveling to continuously update our models and predict where the stars should be at a given destination.
Two, traveling at such high speeds would affect how the spacecraft would "see" the stars around it, due to the relativistic effects introduced - the stars' apparent position and color would be different than what would be recorded while traveling at current spacecraft speeds, for example. However, if we were using a robust relativistic navigation system, we would know where the stars should be, and we would know how they'd look from the spacecraft's frame of reference (in terms of color and position), so we would be able to use that information to determine the spacecraft's location.