Recent analysis, scientific discoveries, and technological developments have moved the concept of using variable, celestial sources as navigation aids for spacecraft from an idea to a foreseeable reality. Variable celestial sources emit fluctuating radiation in contrast to the persistent, fixed radiation emanated by many other celestial sources. The variation of the radiation can be detected and these signals utilized in techniques similar to those used with terrestrial navigation systems.
Similar to Earth‐based GNSS concepts, the unique characteristic of a pulsar‐based navigation system is that a single instrument could conceivably be utilized to generate a full three‐dimensional navigation solution of a vehicle including position, velocity, attitude, and time. With their wide geometric distribution in the sky and periodic radiation, each pulsar appears to act as a kind of natural celestial beacon, or celestial lighthouse.
This chapter provides an overview of this novel variable celestial‐source‐based navigation and timing technology, including concepts for operation and applications. A brief history of the research pursued to date to define and design a navigation system based upon these categories of sources is provided. Source signal processing techniques are presented. The chapter provides a background on the types of variable celestial sources and the characteristics that are beneficial for navigation purposes, as well as the types of detectors that can be employed for their observations. Descriptions of methods for position, velocity, attitude, and time determination are elaborated. Future mission applications are presented, along with the known challenges for deploying this navigation system. As humankind continues to expand exploration into our solar system and beyond, the opportunities that pulsars and other variable celestial sources provide for spacecraft navigation will enable fully independent, autonomous vehicle deep space operation.