Jupiter System Observer Mission Study: Final Report - Lunar and ...

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01 NOVEMBER 2007 2007 JUPITER SYSTEM OBSERVER MISSION STUDY: FINAL REPORT SECTION 4—MISSION CONCEPT IMPLEMENTATION Task Order #NMO710851 For purposes of quantifying the amount of science return from a typical encounter, standard science data quanta have been defined. Since the LA and GPR are limited to close-range operation, we have assumed that each operates for 800 s near closest approach, during which time the LA will generate 10 Mb of data and the GPR will generate 240 Mb. For the remote sensing instruments, the quantum chosen is a data set for which each instrument generates spatial coverage in a square whose height is equal to its cross-track swath width. For the spectrometers, full spectral coverage is obtained over this spatial frame yielding a standard spectral cube for each spectrometer. For the MRC used in stereo, a stereo pair of frames is assumed. Modest levels of data compression (or editing or summing) are assumed for each instrument except the VHS, which must reduce its data in real-time internal Instrument 4-50 to the instrument by a factor of 100. The remote sensing standard data quanta are summarized in Table 4.5-4, and the overlapping FOVs for the various remote sensing instruments in such a data quantum are shown in Figure 4.5-2. The encounter strategy, shown schematically in Figure 4.5-3, is to begin with an empty SSR and a fully charged battery. The MAG and PS/EPD run 100% of the time. The LA and GPR run for 800 s around closest approach. These four instruments collect 380 Mb of data during the encounter period. The remaining 17.2 Gb of capability per encounter is used to return remote sensing data. This data volume corresponds to 149 remote sensing quanta. These remote sensing frames or cubes can be used in a wide variety of ways including regional-scale mapping and high-resolution targets. Figure 4.5-4 summa- Table 4.5-4. Standard Remote Sensing Data Quanta Cross-track spatial pixels Along-track spatial pixels Spectral (or stereo) channels Bits/pixel Compression factor Data Volume (Mb) HRC 2048 2048 1 12 4 12.6 MRC (stereo) 2048 2048 2 12 4 25.2 VHS 480 480 1350 12 100 38 UVS 64 64 1024 12 3 17 TS 32 32 2800 16 2 23 Total 115.8 Figure 4.5-2. Overlapping FOVs of standard remote sensing quantum. The MRC FOV is 10 larger than that of the Hires FOV and is not shown here.
2007 JUPITER SYSTEM OBSERVER MISSION STUDY: FINAL STUDY 01 NOVEMBER 2007 Task Order #NMO710851 SECTION 4—MISSION CONCEPT IMPLEMENTATION rizes the number of standard data sets that can be obtained for each remote sensing instrument over the course of the JSO tour. The numbers for each satellite scale directly with the number of close flybys of each during the tour. Global-scale color and spectral coverage will be obtained on either side of the close encounter period (within a few days of closest approach, but not within a few hours). The best-resolution areas for global coverage for each satellite will be restricted by the available encounter geometries. The encounter geometries at each satellite are determined by the orientation of the line of apsides of the spacecraft orbit about Jupiter relative to the Sun direction, the perijove altitude (i.e., how far inside of a satellite’s orbit the spacecraft orbital perijove is), and whether an encounter is pre- or post-perijove. Figure 4.5-5 shows the sub-spacecraft ground tracks on the Galilean satellites for the sample JSO tour. Note that the approach and departure points (the end points of each ground track) are clustered at low latitudes and within fairly narrow longitude bands. The approach and departure points, along with the solar illumination at the time of a given encounter, restrict those regions that can be globally mapped well during the tour. 4-51 Figure 4.5-3. Schematic showing remote sensing activities for the period three hours prior to satellite closest approach during a flyby. Note that subsequent to this period, samples of high quality science data can still be acquired. Table 4.5-5 summarizes the types of observations that will be taken as a function of time from encounter on a typical flyby (the times in parenthesis in Table 4.5-5 are for a less typical slow flyby of Ganymede during the end game portion of the tour) and the areal coverage possible at each resolution over the course of the tour for each satellite. 4.5.3.6 Elliptical orbit strategy The contents of the science observing scenarios during the elliptical orbit phase (Figure 4.5-6) are limited by the downlink Figure 4.5-4. Number of standard remote sensing data sets that can be returned during the tour for each Galilean satellite.
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