X-ray pulsar-based navigation and timing (XNAV) or simply pulsar navigation is a navigation technique whereby the periodic

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

signals emitted from

pulsars A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Ea ...

are used to determine the location of a vehicle, such as a spacecraft in deep space. A vehicle using XNAV would compare received X-ray signals with a database of known pulsar frequencies and locations. Similar to

GPS The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...

, this comparison would allow the vehicle to calculate its position accurately (±5 km). The advantage of using X-ray signals over radio waves is that X-ray telescopes can be made smaller and lighter. Experimental demonstrations have been reported in 2018.

Spacecraft navigation

Studies

The

Advanced Concepts Team The Advanced Concepts Team is a group of scientists, researchers and young graduates that perform multidisciplinary research within the European Space Agency. Located at the European Space Research and Technology Centre, in the Netherlands, th ...

ESA , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...

studied in 2003 the feasibility of x-ray pulsar navigation in collaboration with the Universitat Politecnica de Catalunya in Spain. After the study, the interest in the XNAV technology within the

European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...

was consolidated leading, in 2012, to two different and more detailed studies performed by GMV AEROSPACE AND DEFENCE (ES) and the National Physical Laboratory (UK).

Experiments

;XPNAV 1: On 9 November 2016, the Chinese Academy of Sciences launched an experimental pulsar navigation satellite called XPNAV 1. XPNAV-1 has a mass of 240 kg, and is in a 493 km × 512 km, 97.41° orbit. XPNAV-1 will characterize 26 nearby pulsars for their pulse frequency and intensity to create a navigation database that could be used by future operational missions. The satellite is expected to operate for five to ten years. XPNAV-1 is the first pulsar navigation mission launched into orbit. ;SEXTANT: SEXTANT (Station Explorer for X-ray Timing and Navigation Technology) is a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

-funded project developed at the

Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...

that is testing XNAV on-orbit on board the

International Space Station The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...

in connection with the

NICER The Neutron Star Interior Composition ExploreR (NICER) is a NASA telescope on the International Space Station, designed and dedicated to the study of the extraordinary gravitational, electromagnetic, and nuclear physics environments embodied by ...

project, launched on 3 June 2017 on the

SpaceX CRS-11 SpaceX CRS-11, also known as SpX-11, was a Commercial Resupply Service mission to the International Space Station, launched successfully on 3 June 2017. The mission was contracted by NASA and was flown by SpaceX. The mission utilized a Falcon ...

ISS resupply mission. If this is successful, XNAV may be used as secondary navigation technology for the planned Orion missions. In January 2018, X-ray navigation feasibility was demonstrated using NICER/SEXTANT on ISS. It reported a 7 km accuracy (in 2 days).

Aircraft navigation

In 2014, a feasibility study was carried out by the National Aerospace Laboratory of Amsterdam, for use of pulsars in place of GPS in navigation. The advantage of pulsar navigation would be more available signals than from satnav constellations, being unjammable, with the broad range of frequencies available, and security of signal sources from destruction by antisatellite weapons.

Types of pulsar for XNAV

Among pulsars,

millisecond pulsars A millisecond (from ''milli-'' and second; symbol: ms) is a unit of time in the International System of Units (SI) equal to one thousandth (0.001 or 10−3 or 1/1000) of a second and to 1000 microseconds. A unit of 10 milliseconds may be called ...

are good candidate to be space-time references. In particular, extraterrestrial intelligence might encode rich information using millisecond pulsar signals, and the metadata about XNAV is likely to be encoded by reference to millisecond pulsars. Finally, it has been suggested that advanced extraterrestrial intelligence might have tweaked or engineered millisecond pulsars for the goals of timing, navigation and communication.

References

External links

Johns Hopkins APL to Develop Deep Space Navigation Network
{{Neutron star Navigational aids Pulsars Celestial navigation