Designing compact X-ray optics for Pulsar-Informed Navigation

This paper describes a kind of natural GPS using stars called pulsars. Pulsars are one kind of neutron star. They emit beams of radiation that appear to pulse as the star spins, like the light from a lighthouse. A particular kind of pulsar, known as a millisecond pulsar, spins and blinks with the consistency of a modern atomic clock. This makes millisecond pulsars a reliable reference for timing and navigation. As an observer moves closer, the flashes, which are traveling at the speed of light, will arrive slightly earlier. And conversely, moving farther away causes the flashes to appear slightly later. It is possible to estimate position relative to the pulses of light. With four pulsars, you can estimate a 4-dimensional state in space and time. In 2017, this was demonstrated using the NICER telescope on the International Space Station for a project called SEXTANT. A smaller telescope could make pulsar navigation a tool for spacecraft. The challenge for small telescopes is that pulsars appear very faint. If a telescope is only sensitive to the ticks of pulsed light, it will make the pulsar clock stand out more clearly. This paper describes pulsars and X-ray telescopes, as well as an approach to design a smaller telescope specifically for observing the brightest millisecond pulsars.