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!  | PED OUTPUT PRODUCT |
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!  /spectre/data1/aroman/proposals/6758.prop
!  Generated by PREPROCESSOR, version 6.3b
!  Date: Wed Jun  5 19:53:10 EDT 1996

Proposal_Information
              Title: Far-UV Airglow and Albedo Observations of Europa and Ganymede
  Proposal_Category: GO
Scientific_Category: SOLAR SYSTEM
              Cycle: 6


Investigators

            PI_Name: Doyle Hall
     PI_Institution: The Johns Hopkins University


           CoI_Name: Paul Feldman
    CoI_Institution: The Johns Hopkins University
            Contact: Y

           CoI_Name: Melissa McGrath
    CoI_Institution: The Space Telescope Science Institute
            Contact: 

           CoI_Name: Darrell Strobel
    CoI_Institution: The Johns Hopkins University
            Contact: 


Abstract:
The recent HST discovery of a molecular oxygen atmosphere on Europa and the ground-based discovery of oxygen molecules trapped in the near-surface material of Ganymede provide a striking confirmation of the prediction that O_2 is a stable end-product of the evolution icy surfaces exposed to charged-particle radiation.  However, questions remain about the nature of the mechanisms that produce the oxygen molecules and excite the observed far-UV emissions. We propose to use the HST GHRS to measure Europa's OI 1304 Angstrom and 1356 Angstrom brightnesses on both leading and trailing hemispheres to establish the long-term stability of the airglow emission, and to determine the magnitude of its leading/trailing hemisphere emission asymmetry. In addition, we propose to search for the same far-UV oxygen emissions on Ganymede, to determine (or place upper limits) on its abundance of gaseous oxygen in both molecular and atomic form. The proposed observations will also provide measurements of Europa's leading and trailing hemisphere geometric albedos, and Ganymede's trailing hemisphere albedo, by using the reflected brightness of the solar CII 1335 Angstrom feature, and will establish the existence of any systematic differences in the abundance of UV-darkening contaminants on the icy surfaces of the satellites.


Questions


    Observing_Description:
We propose three separate observations with the GHRS, all in ACCUM mode using the G140L grating (observing the 1200-1490 Angstrom wavelength interval) with the Large Science Aperture centered on the disk of each satellite. The HST GHRS is uniquely well-suited for this study because of its sensitivity in the far-UV bandpass, and because both satellites fit remarkably well in the Large Science Aperture. Europa is the target of the first two observations, and Ganymede is the third.  Each observation requires 5 HST orbits of exposure, designed to provide a measurement of similar statistical quality as obtained by Hall et al. (1995a), who observed Europa's trailing hemisphere during the DARKTIME segments of 6 HST orbits. (However, during one of the these six orbital exposures Europa drifted significantly relative to the LSA boresight, excluding at least a part of the satellite's disk from the aperture, and the combined spectrum, 7290 sec total duration, has the statistical quality of about five correctly-executed HST orbits of exposure.) The measured brightnesses of the brightest and weakest features in the accumulated Hall et al. (1995a) spectrum were I(1356 Angstrom) = 77 +/- 13 and I(1335 Angstrom) = 30 +/- 11 Rayleighs respectively, indicating a 1-Sigma detection threshold of 10--15 Rayleighs, consistent with the signal-to-noise predicted using the formulae and sensitivities given in the GHRS handbook for a source the size of Europa's disk. Thus, the proposed observations will be able to detect ~ 30 Rayleigh emission feature signals the 2--3,Sigma confidence level on Europa. Because the angular size of Ganymede's disk is larger than Europa's, the same on-disk brightness will produce larger GHRS signal levels, and the 1,Sigma detection threshold for Ganymede will be approximately 30% smaller than for Europa (i.e., 7--10 Rayleighs). DARKTIME is preferred for the proposed observations, because OI 1304 Angstrom terrestrial airglow emissions are bright enough during non-DARKTIME periods to contaminate the GHRS spectra. However, we will acquire the data using short (~ 5 minute) individual exposures that are summed afterwards, so that data obtained during non-DARKTIME segments of orbits can still be used to increase the signal-to-noise ratios in wavelength regions not affected by Earth airglow. The first exposure, obtained when Europa is near western elongation with its trailing hemisphere facing the Earth, will be a close reproduction of the Hall et al. (1995a) observation, and is required to confirm the persistence of the oxygen airglow features originally detected by Hall et al. (1995a) and establish a baseline for comparison with the leading hemisphere observation. The second Europa observation will be acquired approximately 43 hours after the first, allowing Europa to move along its orbit from western elongation to eastern elongation. Even though the order of these two observations can be reversed for scheduling purposes if necessary, we request that both be performed within one Europa orbit because this minimizes the chance that the measurements will be adversely affected by Io torus temporal fluctuations. Europa has a diameter of ~ 3140 km and is typically 4.5 AU from the Earth during HST observations, projecting a disk about 0.95 arcsec in diameter that fits nicely inside the 1.74 arcsec square LSA. These two Europa exposures will allow the direct comparison of the leading/trailing hemisphere oxygen airglow brightnesses and far-UV geometric albedos measured in as short a period as possible. The third exposure targets Ganymede near western elongation.  At a distance of 4.5 AU, Ganymede's 5260 km solid surface projects a disk about 1.61 arcsec in diameter, also nicely compatible with the size of the GHRS LSA.  The goals of this observation are to measure the surface albedo at 1335 Angstrom and search for OI emissions at 1304 and 1356 Angstrom. ,  Bagenal, F. (1994) JGR 99 11043. Broadfoot, A. L., et al. (1979) Science 204 979.  Calvin, W. M. & Spencer, J. R. (1994) Bull. Am. Astr. Soc. 26 1159. Carlson, R. W., et al. (1973) Science 182 53.  Cheng, A. F. (1986) in Satellites pp. 403, Univ. of Ariz. Press, Tucson. Clark, R. N. (1980) Icarus 44 388.  Eviatar, A., et al. (1981) Icarus 47 75.  Eviatar, A., et al. (1985) Icarus 61 185.  Hall, D. T., et al. (1995a) Nature 373 677.  Hall, D. T., et al. (1995b) Division for Planetary Sci. AAS Abstract. Hapke, B., et al. (1981) Icarus 47 361.  Ip, W.-H. (1995) Icarus 115 295.  Johnson, R. E. (1990) Energetic Charged-Particle Interactions with Atmosphere and Surfaces, Springer Verlag, Berlin Heidelberg.  Kumar, S. and Hunten, D. M. (1982) in Satellites pp. 782, Univ. of Ariz. Press, Tucson, Ariz.  Lane, A. L. et al., (1981) Nature 292 38.  Morrison, D. (1977) in Planetary Satellites pp.269, Univ. of Ariz. Press, Tucson, Ariz.  Nelson, R. M., et al. (1987) Icarus 72 358.  Noll, K. et al. (1995) Science, to be submitted. Pospieszalska, M. K. & Johnson, R. E. (1991) Icarus 93 45. Sack, N. J., et al. (1992) Icarus 100 534.  Yung, Y. L. & McElroy, M. B. (1977) Icarus 30 97.

  Real_Time_Justification:
Because these observations target the leading and trailing hemispheres of Europa and Ganymede, they require that each
satellite be observed within specific orbital longitude windows, as can be requested using an established Solar System Target mode.  We request that the trailing and leading hemisphere observations of Europa be performed within one Europa orbit in order to minimize adverse temporal variability effects. Finally, orbital DARKTIME is preferred for all of these observations to minimize terrestrial oxygen airglow contamination.

Calibration_Justification:


      Additional_Comments:



Fixed_Targets


Solar_System_Targets

  Target_Number: 1
    Target_Name: EUROPA-WEST
    Description: SATELLITE EUROPA
        Level_1: STD=JUPITER
        Level_2: STD=EUROPA
        Level_3: 
         Window: 
     OLG OF EUROPA BETWEEN 250 290
           Flux: 
                V = 5.29
                B-V = 0.87
       Comments: Europa at elongation on Jupiter's dusk side. The other
galilean satellites must be separated by more than 10 arcsec
from the target (by default).

  Target_Number: 2
    Target_Name: EUROPA-EAST
    Description: SATELLITE EUROPA
        Level_1: STD=JUPITER
        Level_2: STD=EUROPA
        Level_3: 
         Window: 
     OLG OF EUROPA BETWEEN 70 110
           Flux: 
                V = 5.29
                B-V = 0.87
       Comments: Europa at elongation on Jupiter's dawn side. The other
galilean satellites must be separated by more than 10 arcsec
from the target (by default).

  Target_Number: 3
    Target_Name: GANYMEDE-WEST
    Description: SATELLITE GANYMEDE
        Level_1: STD=JUPITER
        Level_2: STD=GANYMEDE
        Level_3: 
         Window: 
     OLG OF GANYMEDE BETWEEN 250 290
           Flux: 
                V = 4.61
                B-V = 0.83
       Comments: Ganymede at elongation on Jupiter's dusk side. The other
galilean satellites must be separated by more than 10 arcsec
from the target (by default).

  Target_Number: 4
    Target_Name: EUROPA-WEST-2
    Description: SATELLITE EUROPA
        Level_1: STD=JUPITER
        Level_2: STD=EUROPA
        Level_3: 
         Window: 
     OLG OF EUROPA BETWEEN 180 360
           Flux: 
                V = 5.29
                B-V = 0.87
       Comments: 


Generic_Targets


Scan_Data


Visits

      Visit_Number: 01
Visit_Requirements: 
                BETWEEN 21-Jun-1996 AND 01-Aug-1996
                after 02 by 0d to 12d 
  On_Hold_Comments: 
    Visit_Comments: Schedule the observations in a time period bracketing Jupiter opposition (7-Jun-96). This ensures that the duration of each orbit's SHADOW interval is near its maximum for Cycle 6 Jupiter observations.  The G140L ACCUM mode spectra following acquisition will be short exposures (5M) providing an internal monitor of Earth airglow throughout each orbit, and allowing data from the SHADOW regions to be binned separately.

     Exposure_Number: 111
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACQ
            Aperture: 2.0
          Sp_Element: MIRROR-N2
          Wavelength: 
 Optional_Parameters: BRIGHT=RETURN,LOCATE=EXTENDED,SEARCH-SIZE=5
Number_of_Iterations: 1
   Time_Per_Exposure: 5.0 S
Special_Requirements: 
                ONBOARD ACQ FOR 112-114,121-124,131-134,141-144,151-154
            Comments: An acquisition with STEP-TIME=0.2S using the GHRS Side-2.

     Exposure_Number: 112
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: IMAGE
            Aperture: 2.0
          Sp_Element: MIRROR-N2
          Wavelength: 
 Optional_Parameters: 
Number_of_Iterations: 1
   Time_Per_Exposure: 51.2 S
Special_Requirements: 
            Comments: Image the target to verify pointing accuracy.

     Exposure_Number: 113
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G270M
          Wavelength: 2400.
 Optional_Parameters: 
Number_of_Iterations: 1
   Time_Per_Exposure: 81.6 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 114
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G200M
          Wavelength: 2000.
 Optional_Parameters: 
Number_of_Iterations: 1
   Time_Per_Exposure: 788.8 S
Special_Requirements: 
            Comments: Use remainder of first orbit for Side-2 measurements
of the target UV spectral reflectivity.  This time
can't be used for Side-1 spectra because of the 40M
overhead required to switch to side-1.

     Exposure_Number: 121
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 122
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 123
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 124
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: Exposures 121-124 are G140L ACCUM spectra that are not
predicted to yield a SNR greater than about 7, and
FP-SPLIT is not required.  Short exposures allow Earth
airglow lines to be monitored.

     Exposure_Number: 131
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 132
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 133
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 134
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: Exposures 131-134 are G140L ACCUM spectra that are not
predicted to yield a SNR greater than about 7, and
FP-SPLIT is not required.  Short exposures allow Earth
airglow lines to be monitored.

     Exposure_Number: 141
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 142
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 143
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 144
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: Exposures 141-144 are G140L ACCUM spectra that are not
predicted to yield a SNR greater than about 7, and
FP-SPLIT is not required.  Short exposures allow Earth
airglow lines to be monitored.

     Exposure_Number: 151
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 152
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 153
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 154
         Target_Name: EUROPA-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: Exposures 151-154 are G140L ACCUM spectra that are not
predicted to yield a SNR greater than about 7, and
FP-SPLIT is not required.  Short exposures allow Earth
airglow lines to be monitored.

      Visit_Number: 02
Visit_Requirements: 
                BETWEEN 21-Jun-1996 AND 01-Aug-1996
                ORIENT 90D TO 90D
  On_Hold_Comments: 

    Visit_Comments: Schedule the second observation (visit 01) during the next elongation, ensuring that the WEST and EAST are observed in the same Europa orbit.  Note that Visit 1 may be executed first for scheduling purposes, but in that case Visit 2 must follow by 40 to 45H. Short G140L exposures provide an monitor of Earth airglow throughout each orbit.


     Exposure_Number: 211
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACQ
            Aperture: 2.0
          Sp_Element: MIRROR-N2
          Wavelength: 
 Optional_Parameters: BRIGHT=RETURN,LOCATE=EXTENDED,SEARCH-SIZE=5
Number_of_Iterations: 1
   Time_Per_Exposure: 5.0 S
Special_Requirements: 
                ONBOARD ACQ FOR 212-254
            Comments: An acquisition with STEP-TIME=0.2S using the GHRS Side-2.

     Exposure_Number: 212
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: IMAGE
            Aperture: 2.0
          Sp_Element: MIRROR-N2
          Wavelength: 
 Optional_Parameters: 
Number_of_Iterations: 1
   Time_Per_Exposure: 51.2 S
Special_Requirements: 
            Comments: Image the target to verify pointing accuracy.

     Exposure_Number: 213
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G270M
          Wavelength: 2400.
 Optional_Parameters: 
Number_of_Iterations: 1
   Time_Per_Exposure: 81.6 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 214
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G200M
          Wavelength: 2000.
 Optional_Parameters: 
Number_of_Iterations: 1
   Time_Per_Exposure: 516.8 S
Special_Requirements: 
            Comments: Use remainder of first orbit for Side-2 measurements of the target UV spectral reflectivity.  This time can't be used for Side-1 spectra because of the 40M overhead required to switch to side-1.

     Exposure_Number: 221
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 222
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 223
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 224
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: Exposures 221-224 are G140L ACCUM spectra that are not predicted to yield a SNR greater than about 7, and FP-SPLIT is not required. Short exposures allow Earth airglow lines to be monitored.

     Exposure_Number: 231
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 232
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 233
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 234
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: Exposures 231-234 are G140L ACCUM spectra that are not
predicted to yield a SNR greater than about 7, and
FP-SPLIT is not required.  Short exposures allow Earth
airglow lines to be monitored.

     Exposure_Number: 241
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 242
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 243
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 244
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: Exposures 241-244 are G140L ACCUM spectra that are not
predicted to yield a SNR greater than about 7, and
FP-SPLIT is not required.  Short exposures allow Earth
airglow lines to be monitored.

     Exposure_Number: 251
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 252
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 253
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 254
         Target_Name: EUROPA-EAST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

      Visit_Number: 03
Visit_Requirements: 
                BETWEEN 21-Jun-1996 AND 01-Aug-1996
  On_Hold_Comments: 
    Visit_Comments: Schedule the observations in a time period bracketing Jupiter opposition (7-Jun-96). This ensures that the duration of each orbit's SHADOW interval is near its maximum for Cycle 6 Jupiter observations.  The G140L ACCUM mode spectra following acquisition will be short exposures (5M) providing an internal monitor of Earth airglow throughout each orbit, and allowing data from the SHADOW regions to be binned separately.

     Exposure_Number: 311
         Target_Name: EUROPA-WEST-2
              Config: HRS
              Opmode: ACQ
            Aperture: 2.0
          Sp_Element: MIRROR-N2
          Wavelength: 
 Optional_Parameters: BRIGHT=RETURN,LOCATE=EXTENDED,SEARCH-SIZE=5
Number_of_Iterations: 1
   Time_Per_Exposure: 5.0 S
Special_Requirements: 
                ONBOARD ACQ FOR 312-354
            Comments: An acquisition with STEP-TIME=0.2S using the GHRS Side-2.

     Exposure_Number: 312
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: IMAGE
            Aperture: 2.0
          Sp_Element: MIRROR-N2
          Wavelength: 
 Optional_Parameters: 
Number_of_Iterations: 1
   Time_Per_Exposure: 51.2 S
Special_Requirements: 
            Comments: Image the target to verify pointing accuracy.

     Exposure_Number: 313
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G270M
          Wavelength: 2400.
 Optional_Parameters: 
Number_of_Iterations: 1
   Time_Per_Exposure: 81.6 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 314
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G200M
          Wavelength: 2000.
 Optional_Parameters: 
Number_of_Iterations: 1
   Time_Per_Exposure: 788.8 S
Special_Requirements: 
            Comments: Use remainder of first orbit for Side-2 measurements
of the target UV spectral reflectivity.  This time
can't be used for Side-1 spectra because of the 40M
overhead required to switch to side-1.

     Exposure_Number: 321
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 322
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 323
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 324
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: Exposures 321-324 are G140L ACCUM spectra that are not
predicted to yield a SNR greater than about 7, and
FP-SPLIT is not required.  Short exposures allow Earth
airglow lines to be monitored.

     Exposure_Number: 331
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 332
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 333
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 334
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: Exposures 331-334 are G140L ACCUM spectra that are not
predicted to yield a SNR greater than about 7, and
FP-SPLIT is not required.  Short exposures allow Earth
airglow lines to be monitored.

     Exposure_Number: 341
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 342
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 343
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 344
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: Exposures 341-344 are G140L ACCUM spectra that are not
predicted to yield a SNR greater than about 7, and
FP-SPLIT is not required.  Short exposures allow Earth
airglow lines to be monitored.

     Exposure_Number: 351
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 352
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 353
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: 

     Exposure_Number: 354
         Target_Name: GANYMEDE-WEST
              Config: HRS
              Opmode: ACCUM
            Aperture: 2.0
          Sp_Element: G140L
          Wavelength: 1356
 Optional_Parameters: FP-SPLIT=NO,STEP-PATT=5
Number_of_Iterations: 1
   Time_Per_Exposure: 462.4 S
Special_Requirements: 
            Comments: Exposures 351-354 are G140L ACCUM spectra that are not
predicted to yield a SNR greater than about 7, and
FP-SPLIT is not required.  Short exposures allow Earth
airglow lines to be monitored.

Data_Distribution         ! Defaults indicated; change if desired

         Medium: 8MM
Blocking_Factor: 10
        Ship_To: PI_Address
       Ship_Via: 
Recipient_Email: 

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