Station Explorer for X-ray Timing and Navigation Technology
Station Explorer for X-ray Timing and Navigation Technology
NASA has invented a new type of autonomous space navigation that could see human-made spacecraft heading into the far reaches of the Solar System, and even farther - by using pulsars as guide stars. It's called Station Explorer for X-ray Timing and Navigation Technology, or SEXTANT (named after an 18th century nautical navigation instrument), and it uses X-ray technology to see millisecond pulsars, using them much like a GPS uses satellites.
Pulsars are highly magnetised, rapidly rotating neutron stars - the result of a massive star's core collapsing and subsequently exploding. As they spin, they emit electromagnetic radiation. From the right angle they can appear as sweeping beams, like a cosmic lighthouse. They're also extraordinarily regular - in the case of some millisecond pulsars, which can spin hundreds of times a second, their regularity can rival that of atomic clocks.
This is what led to the idea behind SEXTANT. Because these pulsars are so regular, and because they're fixed in position in the cosmos, they can be used in the same way that a global positioning system uses atomic clocks.
SEXTANT works like a GPS receiver getting signals from at least three GPS satellites, all of which are equipped with atomic clocks. The receiver measures the time delay from each satellite and converts this into spatial coordinates. The electromagnetic radiation beaming from pulsars is most visible in the X-ray spectrum, which is why X-ray detection has been employed in SEXTANT.
It could take a few years for the technology to be developed into a navigation system suitable for deep-space vessels, but the concept has been proven. Eventually, SEXTANT could be used to calculate the location of planetary satellites far from the range of Earth's GPS satellites, and assist on human spaceflight missions, such as the space agency's planned Mars mission.
