INSTRUMENT_HOST_ID               = ULY                                      
  INSTRUMENT_ID                    = GAS                                      
  INSTRUMENT_NAME                  = GAS INSTRUMENT                           
  INSTRUMENT_TYPE                  = NEUTRAL PARTICLE DETECTOR                
                                                                              
  Instrument Overview                                                         
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    The properties (density, bulk velocity relative                           
    to the solar system, and temperature) of the local interstellar           
    gas, represented by neutral helium penetrating the heliosphere,           
    will be measured in-situ for the first time by the ULYSSES GAS            
    instrument.  By employing the solar gravitational field as a              
    natural velocity analyser, the bulk velocity relative to the              
    solar system and the temperature of the E as can be derived               
    from the angular distributions of the particles measured in at            
    least two widely separated points in the heliosphere.  The gas            
    density can be determined if a composition corresponding to               
    cosmic abundances is assumed.  The neutral particles are                  
    detected via the secondary electrons or ions which are emitted            
    upon particle impact from a freshly deposited lithium-fluoride            
    (LiF) layer.  The physical principles and assumptions on which            
    the experiment is based, the main technical features of the               
    instrument, and first measurements in space are briefly                   
    described.                                                                
                                                                              
  References:                                                                 
  ========                                                                    
                                                                              
  Banaszkiewicz, M., M. Witte, and H. Rosenbauer, Determination               
  of interstellar helium parameters from the ULYSSES-NEUTRALGAS               
  experiment: Method of data analysis, Astron. Astrophys. Supp.               
  Ser., 120, 1-16, 1996.                                                      
                                                                              
  Witte, M., H. Rosenbauer, E. Keppler, H. Fahr, P. Hemmerich, H.             
  Lauche, A. Loidl, and R. Zwick. The Interstellar Neutral-Gas                
  Experiment On Ulysses, Astron. Astrophys. Suppl. Ser., 333, 1992.           
                                                                              
  Witte, M., H. Rosenbauer, M. Banaszkiewics, and H. Fahr, The                
  Ulysses Neutral Gas Experiment: determination of the velocity               
  and temperature of the interstellar neutral Helium, Adv. Space              
  Res., 13, (6)121, 1993.                                                     
  (https://doi.org/10.1016/0273-1177(93)90401-V)                              
                                                                              
  Witte, M., M. Banaszkiewicz, and H. Rosenbauer, Recent results              
  on the parameters of the interstellar helium from the                       
  ULYSSES/GAS experiment, Space Sci. Rev., 78, 289-296, 1996.                 
  (http://dx.doi.org/10.1007/BF00170815)