Navigating Deep Space By Starlight

In this multiwavelength image, the central object resembles a semi-transparent, spinning toy top in shades of purple and magenta against a black background. The top-like structure appears to be slightly falling toward the right side of the image. At its center is a bright spot. This is the pulsar that powers the nebula. A stream of material is spewing forth from the pulsar in a downward direction, constituting what would be the part of a top that touches a surface while it is spinning. Wispy purple light accents regions surrounding the object. This image combines data from NASA's Chandra, Hubble, and Spitzer telescopes. Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech

Navigating Deep Space by Starlight

On August 6, 1967, astrophysicist Jocelyn Bell Burnell noticed a blip in her radio telescope data. And then another. Eventually, Bell Burnell figured out that these blips, or pulses, were not from people or machines.

This photograph shows astrophysicist Jocelyn Bell Burnell smiling into a camera. She is wearing glasses, a pink collared shirt, and a black cardigan. She is holding a yellow pencil above a piece of paper with a red line across it. There is a tan lampshade and several books in the background. The image is watermarked “Copyright: Robin Scagell/Galaxy Picture Library.”

The blips were constant. There was something in space that was pulsing in a regular pattern, and Bell Burnell figured out that it was a pulsar: a rapidly spinning neutron star emitting beams of light. Neutron stars are superdense objects created when a massive star dies. Not only are they dense, but neutron stars can also spin really fast! Every star we observe spins, and due to a property called angular momentum, as a collapsing star gets smaller and denser, it spins faster. It’s like how ice skaters spin faster as they bring their arms closer to their bodies and make the space that they take up smaller.

This animation depicts a distant pulsar blinking amidst a dark sky speckled with colorful stars and other objects. The pulsar is at the center of the image, glowing purple, varying in brightness and intensity in a pulsating pattern. As the camera pulls back, we see more surrounding objects, but the pulsar continues to blink. The image is watermarked “Artist’s concept.” Credit: NASA’s Goddard Space Flight Center

The pulses of light coming from these whirling stars are like the beacons spinning at the tops of lighthouses that help sailors safely approach the shore. As the pulsar spins, beams of radio waves (and other types of light) are swept out into the universe with each turn. The light appears and disappears from our view each time the star rotates.

A small neutron star spins at the center of this animation. Two purple beams of light sweep around the star-filled sky, emanating from two spots on the surface of the neutron star, and one beam crosses the viewer’s line of sight with a bright flash. The image is watermarked “Artist’s concept.” Credit: NASA's Goddard Space Flight Center.

After decades of studying pulsars, astronomers wondered—could they serve as cosmic beacons to help future space explorers navigate the universe? To see if it could work, scientists needed to do some testing!

First, it was important to gather more data. NASA’s NICER, or Neutron star Interior Composition Explorer, is a telescope that was installed aboard the International Space Station in 2017. Its goal is to find out things about neutron stars like their sizes and densities, using an array of 56 special X-ray concentrators and sensitive detectors to capture and measure pulsars’ light.

This time-lapse of our Neutron star Interior Composition Explorer (NICER) shows how it scans the skies to study pulsars and other X-ray sources from its perch aboard the International Space Station. NICER is near the center of the image, a white box mounted on a platform with a shiny panel on one side and dozens of cylindrical mirrors on the opposite side. Around it are other silver and white instruments and scaffolding. NICER swivels and pans to track objects, and some other objects nearby move as well. The station’s giant solar panels twist and turn in the background. Movement in the sequence, which represents a little more than one 90-minute orbit, is sped up by 100 times. Credit: NASA.

But how can we use these X-ray pulses as navigational tools? Enter SEXTANT, or Station Explorer for X-ray Timing and Navigation Technology. If NICER was your phone, SEXTANT would be like an app on it.

During the first few years of NICER’s observations, SEXTANT created an on-board navigation system using NICER’s pulsar data. It worked by measuring the consistent timing between each pulsar’s pulses to map a set of cosmic beacons.

This photo shows the NICER payload on the International Space Station. Against a black background, tall rectangular solar panels that appear as a golden mesh rise from the bottom of the photo, passing through its middle area. In front of that are a variety of gray and white shapes that make up instruments and the structure of the space station near NICER. Standing above from them, attached to a silver pole, is the rectangular box of the NICER telescope, which is pointing its concentrators up and to the right. Credit: NASA.

When calculating position or location, extremely accurate timekeeping is essential. We usually rely on atomic clocks, which use the predictable fluctuations of atoms to tick away the seconds. These atomic clocks can be located on the ground or in space, like the ones on GPS satellites. However, our GPS system only works on or close to Earth, and onboard atomic clocks can be expensive and heavy. Using pulsar observations instead could give us free and reliable “clocks” for navigation. During its experiment, SEXTANT was able to successfully determine the space station’s orbital position!

A photo of the International Space Station as seen from above. The left and right sides of the image are framed by the station's long, rectangular solar panels, with a complex array of modules and hardware in the middle. The background is taken up fully by the surface of the Earth; lakes, snow-capped mountains, and a large body of water are faintly visible beneath white clouds. Credit: NASA

We can calculate distances using the time taken for a signal to travel between two objects to determine a spacecraft’s approximate location relative to those objects. However, we would need to observe more pulsars to pinpoint a more exact location of a spacecraft. As SEXTANT gathered signals from multiple pulsars, it could more accurately derive its position in space.

This animation shows how triangulating the distances to multiple pulsars could help future space explorers determine their location. In the first sequence, the location of a spaceship is shown in a blue circle in the center of the image against a dark space background. Three pulsars, shown as spinning beams of light, appear around the location. They are circled in green and then connected with dotted lines. Text on screen reads “NICER data are also used in SEXTANT, an on-board demonstration of pulsar-based navigation.” The view switches to the inside of a futuristic spacecraft, looking through the windshield at the pulsars. An illuminated control panel glows in blues and purples. On-screen text reads “This GPS-like technology may revolutionize deep space navigation through the solar system and beyond.” Credit: NASA’s Johnson Space Center

So, imagine you are an astronaut on a lengthy journey to the outer solar system. You could use the technology developed by SEXTANT to help plot your course. Since pulsars are reliable and consistent in their spins, you wouldn’t need Wi-Fi or cell service to figure out where you were in relation to your destination. The pulsar-based navigation data could even help you figure out your ETA!

NASA’s Space Launch System (SLS) rocket carrying the Orion spacecraft launched on the Artemis I flight test. With Artemis I, NASA sets the stage for human exploration into deep space, where astronauts will build and begin testing the systems near the Moon needed for lunar surface missions and exploration to other destinations farther from Earth. This image shows a SLS rocket against a dark, evening sky and clouds of smoke coming out from the launch pad. This is all reflected on the water in the foreground of the photo. Credit: NASA/Bill Ingalls

None of these missions or experiments would be possible without Jocelyn Bell Burnell’s keen eye for an odd spot in her radio data decades ago, which set the stage for the idea to use spinning neutron stars as a celestial GPS. Her contribution to the field of astrophysics laid the groundwork for research benefitting the people of the future, who yearn to sail amongst the stars.

Keep up with the latest NICER news by following NASA Universe on X and Facebook and check out the mission’s website. For more on space navigation, follow @NASASCaN on X or visit NASA’s Space Communications and Navigation website.

Make sure to follow us on Tumblr for your regular dose of space!

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