MSGID: 1:317/3 627201ed   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Proposed spacecraft navigation uses x-rays from dead stars    
      
     Date:   
         May 3, 2022   
     Source:   
         University of Illinois Grainger College of Engineering   
     Summary:   
         The remnants of a collapsed neutron star, called a pulsar, are   
         magnetically charged and spinning anywhere from one rotation   
         per second to hundreds of rotations per second. These celestial   
         bodies, each 12 to 15 miles in diameter, generate light in the   
         x-ray wavelength range.   
      
         Researchers have developed a new way spacecraft can use signals   
         from multiple pulsars to navigate in deep space.   
      
      
      
   FULL STORY   
   ==========================================================================   
   The remnants of a collapsed neutron star, called a pulsar, are   
   magnetically charged and spinning anywhere from one rotation per   
   second to hundreds of rotations per second. These celestial bodies,   
   each 12 to 15 miles in diameter, generate light in the x-ray wavelength   
   range. Researchers at The Grainger College of Engineering, University of   
   Illinois Urbana-Champaign developed a new way spacecraft can use signals   
   from multiple pulsars to navigate in deep space.   
      
      
   ==========================================================================   
   "We can use star trackers to determine the direction a spacecraft is   
   pointing, but to learn the precise location of the spacecraft, we rely   
   on radio signals sent between the spacecraft and the Earth, which can   
   take a lot of time and requires use of oversubscribed infrastructure,   
   like NASA's Deep Space Network," said Zach Putnam, professor in the   
   Department of Aerospace Engineering at Illinois.   
      
   "Using x-ray navigation eliminates those two factors, but until now,   
   required an initial position estimate of the spacecraft as a starting   
   point. This research presents a system that finds candidates for possible   
   spacecraft locations without prior information, so the spacecraft can   
   navigate autonomously."  "Also, our ground communication systems for deep   
   space missions are overloaded right now," he said. "This system would give   
   spacecraft autonomy and reduce the dependency on the ground. X-ray pulsar   
   navigation gets us around that and allows us to determine where we are,   
   without calling."  Putnam said because our atmosphere filters out all   
   the x-rays, you have to be in space to observe them. The pulsars emit   
   electromagnetic radiation that look like pulses because we measure the   
   peak in the x-ray signals every time the pulsar spins around and points   
   toward us -- like the ray of light cast from the beacon on a lighthouse.   
      
   "Each pulsar has its own characteristic signal, like a fingerprint,"   
   he said.   
      
   "We have records of the x-rays over time from the 2,000 or so pulsars   
   and how they've changed over time."  Much like the Global Positioning   
   System, location can be determined from intersection of three signals.   
      
   "The issue with pulsars is that they spin so fast that the signal   
   repeats itself a lot," he said. "By comparison, GPS repeats every two   
   weeks. With pulsars, while there are an infinite number of possible   
   spacecraft locations, we know how far apart these candidate locations   
   are from each other.   
      
   "We are looking at determining spacecraft position within domains that   
   have diameters on the order of multiple astronomical units, like the   
   size of the orbit of Jupiter -- something like a square with one billion   
   miles on a side.   
      
   The challenge we are trying to address is, how do we intelligently observe   
   pulsars and fully determine all possible spacecraft locations in a domain   
   without using an excessive amount of compute resources," Putnam said.   
      
   The algorithm developed by graduate student Kevin Lohan combines   
   observations from numerous pulsars to determine all the possible positions   
   of the spacecraft. The algorithm processes all the candidate intersections   
   in two dimensions or three dimensions.   
      
   "We used the algorithm to study which pulsars we should observe to reduce   
   the number of candidate spacecraft locations within a given domain,"   
   said Putnam.   
      
   Results showed that observing sets of pulsars with longer periods and   
   small angular separations could significantly reduce the number of   
   candidate solutions within a given domain.   
      
   The research was funded in part by NASA.   
      
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_Illinois_Grainger_College_of_Engineering.   
      
   Original written by Debra Levey Larson. Note: Content may be edited for   
   style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Kevin Lohan, Zachary Putnam. Characterization of Candidate   
      Solutions for   
         X-Ray Pulsar Navigation. IEEE Transactions on Aerospace and   
         Electronic Systems, 2022; 1 DOI: 10.1109/TAES.2022.3152684   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2022/05/220503141334.htm   
      
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