Mission Objectives Overview    ===========================      The primary objective for DSPSE was demonstration of high      technology BMDO components.  These included the four advanced      lightweight sensors provided by LLNL, two Inertial      Measurement Units, reaction wheel assemblies, GaAS/Ge solar      arrays, the NiH2 common pressure vessel battery, advanced      release mechanisms, composite structures, and a high-      performance 32-bit Reduced Instruction Set Computer (RISC)      microprocessor.  DSPSE used the Moon (and would have used      Geographos) as targets on which to test the detection and      acquisition capabilities of the sensors at realistic closing      velocities while evaluating the effects of long-term exposure      to a deep space environment [REGEONETAL1994].       The second objective for DSPSE was use of the on-board      technology to acquire data that would be of interest to the      international civilian science community.  Within the Lunar      Mapping phase of the mission, the highest science priority      was acquisition of global multispectral image data.  These      images represent the first global data set in digital form      for the Moon.  The color of the Moon in the visible and      near-infrared is diagnostic of both composition and exposure      history of the regolith material.  Filters were chosen to      provide the continuum response of the Moon to solar      illumination and to detect variations at particular      wavelengths which would indicate presence of specific      minerals, such as plagioclase feldspar.  Sensor coverage is      shown in the table below:       Instrument        Field of View      Wavelengths      (degrees)       (micrometers)      ------------      --------------  ----------------      UVVIS                5.6 x 4.2     0.415 +/- 0.020      0.750 +/- 0.005      0.900 +/- 0.015      0.950 +/- 0.015      1.000 +/- 0.015      0.625 +/- 0.225      NIR                  5.6 x 5.6     1.100 +/- 0.030      1.250 +/- 0.030      1.500 +/- 0.030      2.000 +/- 0.030      2.600 +/- 0.030      2.780 +/- 0.060      LWIR                 1.0 x 1.0     8.750 +/- 0.750      HIRES                0.4 x 0.3     0.415 +/- 0.020      0.560 +/- 0.005      0.650 +/- 0.005      0.750 +/- 0.010      0.600 +/- 0.200      LIDAR Transmitter                       1.064      0.532      LIDAR Receiver         0.057       0.750 +/- 0.350      Star Tracker          28 x 43      0.750 +/- 0.350       Throughout the Lunar Mapping phase of the mission, the LIDAR      system acquired high resolution profiles of lunar topography.      Over those parts of each revolution where radio tracking of      the spacecraft was possible, variations in the gravity field      of the Moon could be measured.  The combination of topography      profiles and gravity maps places important constraints on the      interior structure of the Moon.       The data acquired by Clementine allow identification of major      compositional provinces as well as detailed study of complex      areas.  For example, the South Pole - Aitken Basin was not      only discovered to be a major depression [ZUBERETAL1994] but      it was also found to be compositionally anomalous      [LUCEYETAL1994].  Within the South Pole - Aitken Basin is an      extensive region near the south pole which may be an impact      basin 300 km in diameter, parts of which are never      illuminated by the Sun [SHOEMAKERETAL1994].  If so, water      molecules may be drawn to the 'cold trap' and accumulate in      significant quantity over millions of years      [NOZETTEETAL1994].  The combination of 11-color mapping from      the imaging sensors, topography from the laser altimeter,      gravity information from radio tracking, and other data      represents a major improvement in knowledge about the Moon.      A discussion of impact crater results has been presented by      [PIETERSETAL1994], ancient multi-ring basins have been      discussed by [SPUDISETAL1994], and the Aristarchus region has      been described by [MCEWENETAL1994].      OBSERVATION STRATEGY    ====================      The observation strategy during Lunar Mapping was constrained      primarily by the volume of data that could be downloaded during      each revolution (100 MBytes maximum per revolution).  During      revolutions when the transmission path was partially obstructed      (as during occultations near new and full Moon), the downlink      was reduced to as little as 60 MB.  Against these downlink      constraints, Clementine personnel balanced observation and      compression strategies to achieve the following objectives: (1)      global coverage in 5 UVVIS and 6 NIR bands, (2) continuous LWIR      imaging under each revolution strip, (3) HIRES polar imaging,      and (4) additional HIRES imaging.       Clementine personnel further desired double imaging with the      UVVIS, at long and short exposure times (or different      gain/offset states) in order to acquire the best possible      signal-to-noise ratio (SNR) without saturation.  Mission      planners also sought to reduce the data rate by using an      on-board data compression system.  Compression ratios achieved      were about 5:1 for the UVVIS long exposures, 12:1 for the UVVIS      short exposures, 2.2:1 for the NIR, 1.6:1 for the LWIR, and 3:1      for the HIRES.  These compression ratios varied primarily as a      function of high-frequency noise and scene contrast.  LWIR      images had about five percent bad pixels and about ten percent      noisy pixels.  Because of the poor LWIR compression ratio and      because the array was small (128 x 128), the LWIR data were      acquired uncompressed.  In the HIRES an intensifier reduced      resolution; a resolution element was equivalent to about 3-4      pixels.  Mission planners expected to achieve high compression      ratios (>10:1) but were thwarted by two types of high-frequency      noise: (1) a 'honeycomb' pattern from the intensifier, and (2)      shot noise resulting from use of low gain states during flight.      The HIRES was of greater importance to the planned Geographos      observations and some of its components were believed to have      limited lifetimes, so measures were taken during the Lunar      Mapping phase to minimize its use.       Nominal plan for each systematic mapping revolution was:       Observation                      Compression   Number    Volume      Ratio                                            of       (MB)                                                     Frames      ---------------------------------------------------------------      UVVIS 5-color long exposure          5:1         820       18      UVVIS 5-color short exposure        12:1         820        8      NIR 6-color pole-to-pole           2.2:1        1044       32      10-deg. lat uncompressed UVVIS/NIR   1:1                    7      LWIR pole-to-pole                    1:1         870       14      HIRES  750-nm  lat  +/-  50-90       8:1         600        8      HIRES  4-filter, 10 deg.latitude    12:1         400        4      Dark frames/star cal frames          1:1          68        4      LIDAR altimetry                      N/A         N/A        0*      ---------------------------------------------------------------      TOTALS:                                         4622       95       *LIDAR altimetry data volume was non-zero but small compared      with 1 MB.       The 95 MB/revolution rate was easily returned in the absence of      downlink anomalies and occultation constraints.  For      revolutions including long occultations the strategy      recommended by the science team was to reduce the data volume      by dropping the HIRES color, compressing all of the UVVIS/NIR,      and compressing the LWIR.  In practice this was followed only      approximately because staffing was insufficient to tailor      operations on short time scales.       There were approximately 10 spacecraft upsets or downlink      problems during Lunar Mapping that resulted in loss of all or      part of the data from a revolution.  Gaps from mapping cycle 1      were filled in cycle 2 (at lower resolution in the southern      hemisphere), and gaps in the early part of mapping cycle 2      (longitudes 0-100 W) were recovered during the post-mapping      period.  For the latter parts of cycle 2 (longitudes 0-230 E),      a strategy was implemented to fill gaps in revolutions      immediately following an upset by pointing the spacecraft to      the east and using several revolutions carefully to recover      fully from what had been lost on one.  Most of the HIRES and      LWIR observations were sacrificed during these late recovery      efforts, which were largely successful; but there may remain      small gaps (< 1% of the lunar surface) in the UVVIS/NIR      mapping.  At specific wavelengths, gaps are larger.