PDS_VERSION_ID      = PDS3                                                    
RECORD_TYPE         = FIXED_LENGTH                                            
RECORD_BYTES        = 80                                                      
OBJECT              = TEXT                                                    
  PUBLICATION_DATE    = 2000-07-18                                            
  NOTE                = "Description of JPL IPNG SPK Files"                   
END_OBJECT          = TEXT                                                    
END                                                                           
                                                                              
                                                                              
JPL IPNG SPK files (data type IPN) are reconstructions of the Mars Global     
Surveyor (MGS) spacecraft trajectory merged with ephemerides for solar system 
bodies.  The spacecraft trajectory reconstructions were made by the Jet       
Propulsion Laboratory (JPL) Inner Planet Navigation Group in the course of    
their derivation of Mars gravity models.  These solutions were delivered to   
the JPL Navigation and Ancillary Information Facility (NAIF), where they were 
converted to SPK binary format.  The MGS Radio Science Team (RST) at Stanford 
obtained the spacecraft SPK files and ephemerides of solar system bodies from 
NAIF and merged them to produce IPN files.  The NOTE keyword in the label     
lists the files that were merged to produce the IPN file.                     
                                                                              
Derivation of the Mars gravity field is described by D.E. Smith et al., "The  
Gravity Field of Mars: Results from Mars Global Surveyor", SCIENCE, Vol. 286, 
94-97, 1999.  A more detailed, but somewhat older discussion, can be found    
in  A.S. Konopliv and W. L. Sjogren, "The JPL Mars Gravity Field, Mars50C,    
Based upon Viking and Mariner 9 Doppler Tracking Data", Jet Propulsion        
Laboratory Publication 95-5, Pasadena, CA, 73 pp., 1995.  JPL gravity models  
and MGS spacecraft trajectory reconstructions were carried out under the      
direction of W.L. Sjogren at JPL.                                             
                                                                              
Each IPN file is in NAIF transfer format, compatible with readers in the      
SPICE toolkit (see companion files TK_FTP.TXT, TK_DESCR.TXT, and TK_INSTL.TXT 
in this DOCUMENT directory for more information on the SPICE toolkit and      
files).  Lines in the file are delimited by ASCII carriage-return line-feed   
pairs (ASCII 13 followed by ASCII 10); on some systems this delimiter pair    
may need to be replaced by the default line delimiter (e.g., the ASCII        
line-feed alone on many Unix systems) before the file can be used.  The       
NAIF utilities  SPACIT  or  TOBIN  may then be used to convert from transfer  
format to local binary format.                                                
                                                                              
File names are of the form  ydddeeeC.IPN  where  y  is the least significant  
digit in the year at the beginning of the file,  ddd  is the day-of-year at   
the beginning of the file,  eee  is the day-of-year at the end of the file,   
and  C  is an upper case letter starting with 'A' that indicates the version  
of the file.  The letters are assigned in sequence in the order the versions  
were generated by the MGS RST.                                                
                                                                              
Each IPN file is accompanied by a minimal PDS label with name  ydddeeeC.LBL   
giving basic information (start and stop date/time, spacecraft name, etc.).   
Labels are ASCII files with 80-character record lengths.  Each record ends    
with an ASCII carriage-return line-feed pair in positions 79 and 80.