How zombie stars are going to be the new spacecraft GPS

Contributed by
Jan 23, 2018

For travel beyond Earth, you’re going to need a space-age GPS.

Pulsars, the zombie neutron stars that emerge from immense supernovas, are the navigation system that we didn’t know we needed until now. Some spin and flash so fast (think multiple times per second) they are actually known as millisecond pulsars. Besides being mind-blowing, the most consistent of these can also help future astronauts figure out exactly where they are in the deep void of space.

You know these things are precise when they can be used to calculate the exact position of the International Space Station without needing any intervention from the home planet.

"We use these pulsars the same way we use the atomic clocks in a GPS navigation system,” Keith Gendreau, principal investigator of the recent ISS experiment at NASA’s Goddard Space Flight Center, told That’s how scary accurate they are.

After NASA installed its Neutron-star Interior Composition Explorer (NICER) outside the ISS last year, the space agency kept an eyeball on pulsar activity with 52 X-ray telescopes that went from studying pulsar behavior to joining forces with the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) experiment, and turning into techno-navigators. SEXTANT is a futuristic take on the sextants that once kept ships from getting lost on sea voyages by tracking stars—except its guiding lights are millisecond pulsars.


SEXTANT was put to the test when the ISS was cut off from location information. The instrument had to think for itself to figure out exactly where the space station, zooming in orbit at 17,500 mph, was in space. Amazingly, SEXTANT didn’t turn to Earth. It instead focused NICER on four millisecond pulsars that had already been singled out for their precise flashes. How precise? SEXTANT was able to determine the position of the ISS within 3-10 miles in just under 8 hours.

Obviously, this has nothing on your car or smartphone’s GPS, but considering those wouldn’t even work in low-earth orbit (forget deep space), it’s a launching point, especially if NASA is ever going to send anything else to Pluto after New Horizons. The Deep Space Network (DSN) is a worldwide network of telescopes that uses signals to locate spacecraft by figuring out how long it takes for the outgoing signal to reach the craft from Earth. When the DSN tried to find out exactly where New Horizons was floating around, it took nine hours for that signal to reach the probe and get beamed back.

"Going to Pluto, this type of system has much better capability than we currently have anywhere," Gendreau acknowledged. "DSN can help figure out that you are so many centimeters away from Earth, but in the cross direction, you have very poor information."

DSN does have around 50 missions to keep its telescopic eye on, so SEXTANT is going to take some of that pressure off its computer brain. It gets better. Exploring the outer solar system won’t require all those X-ray scopes initially used. Just one SEXTANT instrument is the size of a poster tube, and weighs no more than 11 pounds. So the price won’t give NASA sticker shock, either.

Now when are we going to blast another satellite off to Pluto?