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   Computes the thrust and fuel consumed for thrusters. 
   The units in this model will depend on the units in the database. 
   p must correspond to the database units. 
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   Form:
   [thrust, dF, impulse, iSP] = REA( id, p, dT, database )
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   Inputs
   ------
   id              (:)    Thruster ids
   p               (:)    Pressure
   dT              (:)    Pulsewidth (sec)
   database        (1,:)  Database name

   -------
   Outputs
   -------
   thrust          (:)    Thrust
   dF              (:)    Fuel consumed
   impulse         (:)    Total impulse per thruster 
   iSp             (:)    Specific impulse

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