X-ray pulsar-based navigation
X-ray pulsar-based navigation and timing (XNAV) is a theoretical navigation technique whereby the periodic X-ray signals emitted from pulsars 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 triangulate 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.
SEXTANT (Station Explorer for X-ray Timing and Navigation Technology) is a NASA-funded project developed at the Goddard Space Flight Center that is testing XNAV on-orbit on board the International Space Station in connection with the NICER project, launched on 3 June 2017 on the SpaceX CRS-11 ISS resupply mission. If this is successful, XNAV may be used as secondary navigation technology for the planned Orion missions.
On 9 November 2016 the Chinese Academy of Sciences launched an experimental pulsar navigation satellite called XPNAV 1. 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.
The Advanced Concepts Team 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 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).
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.
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- Becker, Werner; Bernhardt, Mike G.; Jessner, Axel (2013-05-21). "Autonomous Spacecraft Navigation With Pulsars". arXiv: [astro-ph.HE]. doi:10.2420/AF07.2013.11.
- "NICER Manifested on SpaceX-11 ISS Resupply Flight". NICER News. NASA. December 1, 2015. Retrieved June 14, 2017.
Previously scheduled for a December 2016 launch on SpaceX-12, NICER will now fly to the International Space Station with two other payloads on SpaceX Commercial Resupply Services (CRS)-11, in the Dragon vehicle's unpressurized Trunk.
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- "DEEP SPACE NAVIGATION WITH PULSARS". GSP Executive Summary. ESA, General Studies Programme.
- Bauke Stelma (8 June 2015). "Pulsar navigation: piloting aircraft with the aid of the stars". ExtremeTech.
- Autonomous Spacecraft Navigation With Pulsars, W.Becker, M.G. Bernhardt & A.Jessner, in Acta Futura 2013
- Johns Hopkins APL to Develop Deep Space Navigation Network
- US Government Contract Proposal for X-Ray Pulsar Based Navigation and Time Determination
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