The ORPA directory is subdivided into three subdirectories.  These directories
(ORB2200, ORB2300, ORB2400) contain full resolution data for orbits 
1850-2199. 

Data are organized into single orbit files which follow the naming convention 
ORBxxxx.RDR where xxxx is a four digit orbit number.  In addition, for each 
data file there is a label file which describes the file characteristics, 
such as number of records, record length, etc. called ORBxxxx.LBL.