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Navigation technique employing X-ray signals emitted by pulsars
X-ray pulsar-based navigation and timing (XNAV) or simply pulsar navigation is a 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 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.[1][2][3] Experimental demonstrations have been reported in 2018.[4]
Spacecraft navigation
Studies
The Advanced Concepts Team of ESA studied in 2003 the feasibility of x-ray pulsar navigation[5] 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).[6]
Experiments
XPNAV 1
On 9 November 2016, the Chinese Academy of Sciences launched an experimental pulsar navigation satellite called XPNAV 1.[7] XPNAV-1 has a mass of 240 kg, and is in a 493 km × 512 km, 97.41° orbit.[7] 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.[8]
SEXTANT
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.[9] If this is successful, XNAV may be used as secondary navigation technology for the planned Orion missions.[10] In January 2018, X-ray navigation feasibility was demonstrated using NICER/SEXTANT on ISS.[11] It reported a 7 km accuracy (in 2 days).[12]
Among pulsars, millisecond pulsars are good candidate to be space-time references.[14] 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.[15] Finally, it has been suggested that advanced extraterrestrial intelligence might have tweaked or engineered millisecond pulsars for the goals of timing, navigation and communication.[16]
^"NICER Manifested on SpaceX-11 ISS Resupply Flight". NICER News. NASA. 1 December 2015. Retrieved 14 June 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.
^Sullivan, W. T. III (1993). "Astrophysical Coding: A New Approach to SETI Signals". Progress in the search for extraterrestrial life : 1993 Bioastronomy Symposium, Santa Cruz, California, 16-20 August 1993. Astronomical Society of the Pacific. ISBN 0-937707-93-7. OCLC32232716.
