The ORPA directory is divided into six subdirectories.  These directories
(ORB2500, ORB02600, ORB02700, ORB2800, ORB2900, and ORB3000) contain full 
resolution data for orbits 2500-3099. 

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.