China's revolutionary deep-space navigation system for future spacecraft



This article was originally published in the Bristol Post and written by Ashley Dove-Jay.


Later this month, China is to launch XPNAV-1, the X-ray Pulsar Navigation satellite. This pioneering spacecraft will be used to build and map out a revolutionary deep-space navigation system, pulsar navigation.

Think of what they’re building as GPS, but for spacecraft travelling between the planets and stars. Instead, they’re not using a network of GPS satellites for triangulation and navigation, they’re using an array of 26 X-ray binary pulsars.

“An array of what!?” I hear you asking?

Elon Musk is the only person I can think of that would not be laughed off the stage for making this ambitious announcement. He is the modern-day equivalent of Henry Ford, Thomas Edison, and Isambard Brunel rolled into one person.

An X-ray binary pulsar is composed of two stars orbiting one another. One of these stars is a neutron star and the other is a typical star like our Sun. Only, the rapidly spinning neutron star is quite literally sucking the life out of its neighbour and emitting powerful X-rays from its magnetic north and south poles in the process of doing so.

By neutron star, I mean a star almost entirely composed of neutrons. By rapidly spinning, I mean a day on one of these stars is somewhere between one and ten thousandths of a second. Several hundred days would zip by in the blink of an eye.

These truly bizarre oddities of nature are born deep in the crucibles of massive stars during the obliterating act of supernova explosions. They are so dense; a heaped tablespoons worth of typical neutron star would weigh about as much as the UK; the island.

The geographic poles and magnetic poles of planets and stars aren’t typically in the same place. Our magnetic North Pole is some 300 miles away from the geographic North Pole the Earth spins on. Because of this discrepancy, as a neutron star spins, you’d see it pulsing several hundred times per second if you were up in space observing it with X-ray glasses. Hence the name X-ray binary pulsar.

So regular are these pulses, they’re about ten thousand times more accurate than the atomic clocks used on GPS satellites for triangulation. With current technology, using this pulsar navigation system, a spacecraft could almost immediately know where it is in this corner of the galaxy to an accuracy of about 100m. The theoretical limit for this system is about 10m.

Not only is this level of precision far higher than current capabilities, it allows spacecraft to autonomously navigate by themselves using these natural and very distant beacons, without the need for communication with us on Earth. This has obvious advantages for spacecraft in the far reaches of our solar system, where the time delays in communications with Earth and commands to the spacecraft can takes hours.

But more immediately, pulsar navigation would allow for much more precise autonomous formation flying of satellite constellations orbiting the Earth. Broadly speaking, more could be achieved with less. Fewer satellites would be needed to achieve things like space-based Internet and real-time continuous Earth observation networks. Military applications? Of course.

Early next year, NASA intends to launch its own version of the Chinese XPNAV-1. We can expect the pulsar navigation system to come online in about a decade.



Ashley Dove-Jay has a PhD in aerospace engineering from the University of Bristol and is a space engineer at Oxford Space Systems with a broad background in the space arena.