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!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!
! SDDL Name:    TDRS_USAGE.SDDL
!
! Purpose:      This file defines the relation "tdrs_usage". 
!
! Modification History:
!
!   Date       OPR      Who                       Reason
! --------   -------    ---   -------------------------------------------------
! 10-28-94   26036      sss   Original Version
! 04-03-96   31186      nlc   Index should be on all 4 fields
!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!

INCLUDE   ZSPSS_USER_TYPES.SDDL

LANGUAGE  FORTRAN, SQL

RECORD  TDRSUS_TYPE

   DESCRIPTION       "This relation contains a table of Tracking and Data
                      Relay System (TDRS) satellite IDs and the time intervals
                      over which the HST will communicate with those 
                      satellites.   
  
                      During normal operations, HST can use two TDRS
                      satellites for communications with the ground.
                      NASA assigns HST two out several TDRS satellites 
                      for periods expected to be on the order months or years. 
                      These satellites are designated TDRSaaa;  where
                      aaa is the west longitude (degrees) position of the 
                      TDRS spacecraft in geosynchronous orbit.  

                      The TDRS system is expected to change.   More TDRS 
                      satellites could be launched.   More ground stations 
                      could be installed.  Satellites could fail.  And 
                      satellites could be moved to new locations.

                      By convention, the HST project considers one satellite 
                      to be the 'West' satellite and the other to be the 
                      'East' satellite.   The 'East/West' designation is
                      arbitrary.  But in general, the 'East' satellite is 
                      located over the eastern hemisphere and the 'West' 
                      satellite is located over the western hemisphere.

                      This relation indicates the time periods over which 
                      specific TDRS satellites are assigned to be the 'East' 
                      and 'West' satellites.

                      Whenever NASA assigns the HST project a new TDRS
                      satellite (changes the name of a satellite) a new
                      record must be added to this relation.  This new
                      record should indicate the new TDRS ID (East or West)
                      and the start time for which it is to be used.  The new 
                      record should have an end time well beyond the expected 
                      lifetime of the HST.  The latest record (prior to the 
                      addition of the new record) should have the end time 
                      changed to one second less than the start of the new 
                      record.  

                      Records for East and West satellites should have 
                      continuous time periods (no gaps or overlapping
                      intervals).  'Old' records should NEVER be deleted
                      so that old test data will continue to work correctly."


   FIELD  tdrs_id
      TYPE           c7
      DESCRIPTION    "The TDRS ID.  It is of the form 'TDRSaaa' where aaa 
                      is the west longitude (degrees) of the TDRS satellite"
   END_FIELD


   FIELD  location
      TYPE           c1
      DESCRIPTION    "The Location of the TDRS satellite.  E = East, W = West"
      DISCRETE       "E", "W"
   END_FIELD


   FIELD  start_time
      TYPE SOGS_CHAR_TIME_TYPE
      DESCRIPTION    "This is the start time for the interval when the TDRS 
                      will be used."
   END_FIELD
  

   FIELD  end_time
      TYPE SOGS_CHAR_TIME_TYPE
      DESCRIPTION    "This is the end time for the interval when the TDRS will 
                      be used." 
   END_FIELD

END_RECORD

RELATION tdrs_usage

   TYPE              TDRSUS_TYPE

   DESCRIPTION       "TDRS Usage Relation" 

   SUBSYSTEM_USING   "SPSS"

   INDEX tdrs_usage_1
      TYPE           unique, clustered
      FIELDS         tdrs_id, location, start_time, end_time
   END_INDEX
   
END_RELATION

INSTANCE  tdrs_usage 

   GLOBAL
   TYPE  TDRSUS_TYPE 

END_INSTANCE 

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