Global Positioning System (GPS) to get us to our location safely, whether we are in a plane, boat, train, or car. This system also provides information for agriculture, environmental, public safety, recreation, and mapping applications. GPS satellites in orbit make this possible by sending specific signals that allow a receiver to triangulate our position. Ironically, even though the satellites are in space, GPS does not work in space outside of Earth’s orbit and never was intended to as the satellites point their signal at the Earth. A similar system is used where radio signals are sent from different points on Earth out into space so that we can direct robotic spacecraft to their destination safely. The bad part about this system is that the farther from Earth the spacecraft is, the less precision that can be achieved. The farthest spacecraft that we have, the Voyager probes, are only known at an approximate location within several square miles. If we are ever to venture out further than our solar system then we are going to need a better system because our current system simply will not work around other stars.
Max-Planck Institute for Extraterrestrial Physics in Garching, Germany have found these reference points with pulsar stars. Pulsar stars are a form of deceased star that emits a detectable x-ray signal that repeats with an exact frequency that is related to the rotation speed of the pulsar. By comparing several signals from different pulsars and comparing them to what would be expected at a reference point, a fairly precise location and velocity can be found. It isn’t quite clear if 3 to 6 pulsars would give an accurate enough position but it may very well be possible to keep track of dozens of pulsars, with each additional pulsar being tracked adding to the precision of the data.
ability to shoot down satellites and because of this, several countries operate independently operated and controlled GPS systems such as the U.S., E.U., Russia, China, and India.