      SUBROUTINE BKSIDE(GET,ALONG,IBACK)
C-----FIND SPACECRAFT IN SHADE OF THE MOON FOR BACKSIDE DATA
C-----ALPHA=ARCOS(R/(R+H)); AT 50,110 AND 125 KM THEN 13,20 AND21DEGREE
C-----ALPHA = 25 DEGREES LONG COVERS ALL CASES
C A15 SUBSOLAR =133.8 - .5092*GETHR   CF. HARTUNG 1972
C A16 SUBSOLAR =143.6 - .5084*GETHR
C     BLOW=SUBSOLAR +90+25
C     BHI =SUBSOLAR +90+25+130
      BLONG=ALONG
      IF(BLONG.LT.0.0) BLONG=BLONG+360.
C A15 BLOW=248.8-.5092*GET/3600.
C A16 BLOW=258.6-.5084*GET/3600.
      BLOW=258.6-.5084*GET/3600.
      BHI =BLOW+130.
      IBACK=0
      IF(BLONG.GT.BLOW.AND.BLONG.LT.BHI) IBACK=1
      RETURN
