X-ray pulsar-based navigation and timing (XNAV) or simply pulsar navigation is a navigation technique whereby the periodic
X-ray
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
signals emitted from
pulsars
A pulsar (''pulsating star, on the model of quasar'') 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 pointin ...
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, this comparison would allow the vehicle to calculate its position accurately (±5 km). The advantage of using X-ray signals over
radio waves
Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths ...
is that
X-ray telescopes
An X-ray telescope (XRT) is a telescope that is designed to observe remote objects in the X-ray spectrum. X-rays are absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, ...
can be made smaller and lighter. Experimental demonstrations have been reported in 2018.
Spacecraft navigation
Studies
The
Advanced Concepts Team
Advanced Concepts Team (ACT) is a research lab within the European Space Agency tasked to "... monitor and perform research on advanced space concepts and technologies, preparing ESA for any disruptive change to come.". Located at the European ...
of
ESA 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
The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...
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
The Chinese Academy of Sciences (CAS; ) is the national academy for natural sciences and the highest consultancy for science and technology of the People's Republic of China. It is the world's largest research organization, with 106 research i ...
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 agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
-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 ...
that is testing XNAV on-orbit on board the International Space Station
The International Space Station (ISS) is a large space station that was Assembly of the International Space Station, assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United ...
in connection with the NICER 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 9 ...
ISS resupply mission.
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
A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The first constellations were likely defin ...
, being unjammable, with the broad range of frequencies available, and security of signal sources from destruction by anti-satellite weapons.
Types of pulsar for XNAV
Among pulsars, millisecond pulsars 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