The ORPA directory is contains one subdirectory.  This directory
(ORB0550) contains full resolution data for orbits 550-599. 
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.