PDS_VERSION_ID        = PDS3                                                  
RECORD_TYPE           = STREAM                                                
OBJECT                = TEXT                                                  
  PUBLICATION_DATE      =  " "                                                
  NOTE                        = "Experiment description for the               
                                 Solar Gravitational Redshift Experiment      
                                 conducted starting in 1989 through 1991      
                                 (DOY 339 through DOY 334). Formatted for     
                                 display or printing with up to 78 constant-  
                                 width characters per line."                  
END_OBJECT            = TEXT                                                  
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      From the October 1989 Galileo launch to the first December 1990 Earth   
gravity assist, one-way noncoherent radio Doppler data were generated         
regularly at 70-meter DSN stations.  This effectively yielded measurements of 
frequency variations in the Galileo spacecraft's crystal oscillator (USO) at  
heliocentric distances ranging from 0.7 to 1.3 astronomical units (1.0 x 10^8 
1.9 x 10^8 km).                                                               
                                                                              
      The basic idea of this experiment is to determine the spacecraft's      
heliocentric position by fitting the coherent radio tracking data, and then   
to use the noncoherent data to determine the relativistic frequency shift in  
the USO as a function of heliocentric distance.  Because of the unique        
character of the Galileo trajectory over the 14-month experiment, it is       
possible to separate the frequency shifts predicted by general relativity     
from the USO's intrinsic frequency variations, in particular the random walk  
in the USO frequency over the duration of the experiment.                     
                                                                              
      The published experimental results verify the total frequency shift     
predicted by general relativity to 0.5% accuracy, while the effect of solar   
gravitation on the clock frequency is verified to an accuracy of 1%.  Both    
accuracies represent the investigators' best estimate of realistic standard   
error.  This test of the gravitational redshift provides a fundamental test   
of Einstein's equivalence principle (EEP), upon which general relativity and  
all other metric theories of gravitation are based.  The experiment           
demonstrates that the piezoelectric mechanical vibrations of a crystal lattice
vary with solar gravitational potential as predicted by the EEP.              
Complementary ground-based experiments using solar spectral lines demonstrate 
to about the same 1% accuracy that the EEP is also satisfied for atomic       
transition energies within the Sun's gravitational field.  Although this      
agreement between the two experiments, and the fact that they both agree with 
the EEP, is what theorists expect, it is satisfying to have definite          
verification of the theoretical predictions, even at the 1% level.