Researchers at the University of Illinois Urbana-Grainger Champaign’s College of Engineering devised a new method for spacecraft to travel in deep space by combining signals from many pulsars.
Pulsars are the magnetically charged leftovers of a shattered neutron star that spin at speeds ranging from one to hundreds of rotations per second. The x-ray wavelength range is generated by these celestial bodies, which are each 12 to 15 miles in diameter.
“We can use star trackers to determine the direction a spacecraft is pointing, but to learn the precise location of the spacecraft, we rely on radio signals sent between the spacecraft and the Earth, which can take a lot of time and requires use of oversubscribed infrastructure, like NASA’s Deep Space Network,” said Zach Putnam, Professor in the Department of Aerospace Engineering at Illinois.
“Using x-ray navigation eliminates those two factors, but until now, required an initial position estimate of the spacecraft as a starting point. This research presents a system that finds candidates for possible spacecraft locations without prior information, so the spacecraft can navigate autonomously.”
“Also, our ground communication systems for deep space missions are overloaded right now,” he said. “This system would give spacecraft autonomy and reduce the dependency on the ground. X-ray pulsar navigation gets us around that and allows us to determine where we are, without calling.”
Because our atmosphere filters out all x-rays, you have to be in space to see them, according to Putnam. Since we detect the peak in the x-ray emissions every time the pulsar spins around and points toward us, like the ray of light cast from a lighthouse beacon, the pulsars generate electromagnetic radiation that looks like pulses.
“Each pulsar has its own characteristic signal, like a fingerprint,” he said. “We have records of the x-rays over time from the 2,000 or so pulsars and how they’ve changed over time.”
The intersection of three signals, similar to the Global Positioning System, can be used to identify location. Kevin Lohan, a PhD student, created an algorithm that combines observations from many pulsars to calculate all of the spacecraft’s probable positions. In two or three dimensions, the algorithm processes all of the candidate intersections.