PDS_VERSION_ID                    = PDS3                                      
RECORD_TYPE                       = STREAM                                    
                                                                              
OBJECT                            = SPACECRAFT_INSTRUMENT                     
SPACECRAFT_ID                     = "IRAS"                                    
INSTRUMENT_ID                     = "FPA"                                     
                                                                              
OBJECT                            = INSTRUMENT_INFORMATION                    
INSTRUMENT_NAME                   = "FOCAL PLANE ARRAY"                       
INSTRUMENT_TYPE                   = "DETECTOR ARRAY"                          
INSTRUMENT_DESC                   = "                                         
                                                                              
The IRAS Focal Plane Array was located at the focal plane of the IRAS         
Ritchey-Chretien telescope.  The mirror surfaces were beryllium, and the      
baffles were aluminum coated with Martin Optical black.  The telescope        
had an entrance pupil diameter of 57 cm, and a central obscuration            
diameter of 24 cm, for an effective collecting area of 2019 cm+2.  The        
measured system focal length was 545 cm and the system F/number was           
9.56.  The measured plate scale at the focal plane was                        
1.585 mm/arcminute.  Imaging was diffraction limited at 25, 60 and 100        
microns, but not at 12 microns.  The telescope was cooled by contact          
with the superfluid helium tank to temperatures ranging from 2 to 5 K.        
The operating temperature of the FPA was 2.6 K.                               
                                                                              
The FPA contains 62 infrared detectors, divided into eight parallel modules,  
two for each color band. Each module contains either seven or eight detectors.
The layout of the detectors is given in the IRAS Explanatory Supplement. The  
detectors were rectangular with their narrow dimension arrayed parallel to the
scan path of infrared sources. The design was such that the image of a real   
source would cross a detector in one module and subsequently cross another    
detector of the same band in the second module, providing a                   
'seconds-confirmation'. This allows for the discrimination between real and   
spurious sources, such as cosmic rays.                                        
                                                                              
The infrared detectors were sampled at 16, 16, 8, and 4 Hz at 12, 25, 60, and 
100 microns, respectively. The response functions of the 4 spectral bands     
used in the focal plane array are given in the IRAS Spectral Response dataset 
distributed through PDS and are listed in the IRAS Explanatory Supplement.    
                                                                              
Output from FPA detectors is typically reported in units of flux density      
(Jansky, where 1 Jy = 1.e-26 Watt/(meter^2)/Hz), calculated from inband flux  
(Watts/meter^2) assuming the external source function to be proportional to   
1/frequency. Jy (BD) is converted to Watt/(meter^2) (IB) by the relation      
BD*K=IB, where K is given in MOSHIRETAL1989 and is listed below:              
                                                                              
                        Wavelength         K                                  
                           12          1.348e-13                              
                           25          5.155e-14                              
                           60          2.577e-14                              
                          100          1.000e-14                              
                                                                              
for more information see BEICHMANETAL1988.  "                                 
                                                                              
END_OBJECT                                   = INSTRUMENT_INFORMATION         
                                                                              
OBJECT                          = INSTRUMENT_REFERENCE_INFO                   
  REFERENCE_KEY_ID              = "BEICHMANETAL1988"                          
END_OBJECT                      = INSTRUMENT_REFERENCE_INFO                   
                                                                              
OBJECT                          = INSTRUMENT_REFERENCE_INFO                   
  REFERENCE_KEY_ID              = "MOSHIRETAL1989"                            
END_OBJECT                      = INSTRUMENT_REFERENCE_INFO                   
                                                                              
END_OBJECT                      = SPACECRAFT_INSTRUMENT                       
                                                                              
END