Millimeter pulsars can be used for universal position system accurate today to ±5 km in the solar system and beyond and soon to meters. (arxiv 22 pages) By comparing pulse arrival times measured on-board a spacecraft with predicted pulse arrivals at a reference location, the spacecraft position can be determined autonomously and with high accuracy everywhere in the solar system and beyond. The unique properties of pulsars make clear already today that such a navigation system will have its application in future astronautics. In this paper we describe the basic principle of spacecraft navigation using pulsars and report on the current development status of this novel technology.
Autonomous spacecraft navigating with pulsars is feasible when using either phased-array radio antennas of at least 150 square meter antenna area or compact light-weighted X-ray telescopes and detectors, which are currently being developed for the next generation of X-ray observatories. Using the X-ray signals from millisecond pulsars we estimated that navigation would be possible with an accuracy of ±5 km in the solar system and beyond. The error is dominated by the inaccuracy of the pulse profiles templates that were used for the pulse peak fittings and pulse-TOA measurements. As pulse profiles templates are known with much higher accuracy in the radio band, it is possible to increase the accuracy of pulsar navigation down to the meter scale< by using radio signals from pulsars for navigation.
Pulsar-based navigation systems can operate autonomously. This is one of their most important advantages, and is interesting also for current space technologies; e.g., as augmentation of existing GPS/Galileo satellites. Future applications of this autonomous navigation technique might be on planetary exploration missions and on manned missions to Mars or beyond.
Currently positioning relies on Earth-based tracking stations to work out a spacecraft’s distance using radio waves, a process that is accurate to within a meter or so. That’s fine for the radial distance, but tracking a spacecraft’s angular position is much harder because of the limited angular resolution of radio antennas. The current technology produces an uncertainty of about four kilometers per astronomical unit of distance between Earth and the spacecraft. So for a spacecraft at the distance of Pluto, that’s an uncertainty of 200 kilometers and at the distance of Voyager 1, the uncertainty is 500 kilometers.
Today, about 2200 rotation-powered pulsars are known. The next generation of radio observatories are expected to reveal tens of thousands more. About 150 have been detected in the X-ray band, and approximately 1/3 of them are millisecond pulsars. In the past 30−40 years many of them have been regularly timed with high precision especially in radio observations. Consequently, their ephemerides (RA, DEC, P, P , binary orbit parameters, pulse arrival time and absolute pulse phase for a given epoch, pulsar proper motion etc.) are known with very high accuracy. Indeed, pulsar timing has reached the 10^−15 fractional level, which is comparable with the accuracy of atomic clocks. This is an essential requirement for using these celestial objects as navigation beacons, as it enables one to predict the pulse arrival time of a pulsar for any location in the solar system and beyond.
Silicon pore optics (a) and glass micropore optics (b) represent novel developments for light-weighted X-ray mirrors of the next generation of X-ray observatories. Both mirror types will be used in Wolter- I configuration (c) to focus X-rays in a double reflection.
Active Pixel – Power consumption including electronics, filter wheel and temperature control was ca. 250 W. The mass of the focal plane, including shielding and thermal interface, was about 15 kg but could be reduced in a more specific design of an X-ray-pulsar navigator
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