| MISSION_DESCRIPTION |
Mission Overview
================
The Deep Space Program Science Experiment (DSPSE), first in
a planned series of technology demonstrations jointly
sponsored by the Ballistic Missile Defense Organization
(BMDO) and the National Aeronautics and Space Administration
(NASA ), was launched on 1994-01-25 aboard a Titan IIG
rocket from Vandenburg Air Force Base in California. The
mission included two months of systematic lunar mapping
(1994-02-26 through 1994-04-21), which was to have been
followed by a flyby of the near-Earth asteroid Geographos
(1994-08-31). A software error, combined with improbable
hardware conditions, on 1994-05-07 led to accidental spin-up
of the spacecraft and loss of attitude control gas. This
precluded the flyby of Geographos. The spacecraft itself was
affectionately known as Clementine since, as in the song of
the same name, it would be 'lost and gone forever' after
completing its short mission.
Clementine's primary objective was qualification of light
weight imaging sensors and component technologies (including
a star tracker, inertial measurement unit, reaction wheel,
nickel hydrogen battery, and solar panel) for the next
generation of Department of Defense (DoD) spacecraft.
DSPSE represented a new class of small, low cost, and
highly capable spacecraft that fully embraced emerging
lightweight technologies to enable a series of long-duration
deep space missions. A second objective was return of data
about the Moon and Geographos to the international civilian
scientific community.
BMDO assigned responsibility for the Clementine spacecraft
design, manufacture, integration, and mission execution to
the Naval Research Laboratory (NRL). Lawrence Livermore
National Laboratory (LLNL) provided lightweight imaging
sensors developed under the sponsorship of BMDO. Goddard
Space Flight Center (GSFC) and the Jet Propulsion Laboratory
(JPL) provided mission design and navigation services. The
Deep Space Network (DSN) provided tracking through JPL. NASA
was responsible for the scientific return from the mission.
Further information on the Clementine Mission can be found
in [NOZETTEETAL1994] and [REGEONETAL1994].
Mission Phases
==============
Mission phases were defined for significant spacecraft activity
periods. During orbital operations a 'cycle' was the time
required for the Moon to rotate once under the spacecraft
(about 28 days). The 'revolution number' refers to an observational
pass over the moon. The revolution number was incremented by one
each time the spacecraft passed over the south pole prior to the
beginning of data acquisition. Revolution number was used in lieu
of orbit number because of the way the orbit number was defined by
the mission. The orbit number was incremented each time the
spacecraft passed through the equatorial plane on the sunlit side
of the Moon. Thus, the orbit number generally changed in the
middle of an observational pass. This proved to be awkward in
defining the data acquired by a single pass over the Moon.
PRE-LAUNCH
----------
Clementine moved from concept to launch in a little over
two years. Significant events during the Pre-Launch phase
of the mission included:
1991-11-19 Naval Research Laboratory (NRL) briefed by
the Space Defense Initiative Organization
(SDIO) on the Clementine concept
1992-01-12 NRL tasked with 2 month Clementine study
1992-02-25 NRL tasked by SDIO to be Clementine lead
1992-03-16 Clementine Concept Definition Review
1992-04-01 Clementine Concept Definition completed;
begin Program Management and System Design
1992-05-01 Begin Systems Engineering and Testing
1992-05-13 Clementine System Requirements Review
1992-06-01 Begin Ground Subsystems Development
1992-07-30 Preliminary Design Review
1992-10-20 Launch Range Introduction (Review)
1992-11-05 Sensor Critical Design Review
1992-11-16 Spacecraft Vehicle Critical Design Review
1993-06-01 Begin Spacecraft Integration
1993-07-01 Begin Ground System Integration and Testing
1993-10-01 Begin Spacecraft Assembly Testing
1993-12-01 Begin Launch Operations and Testing
Spacecraft Id : CLEM1
Target Name : MOON
Mission Phase Start Time : 1991-11-19
Mission Phase Stop Time : 1994-01-25
Spacecraft Operations Type : ORBITER
LAUNCH
------
The Clementine spacecraft was launched on 1994-01-25,
from Vandenburg Air Force Base in California. It went
into a 226-km by 259-km geocentric orbit at an
inclination of 67 degrees.
Spacecraft Id : CLEM1
Target Name : MOON
Mission Phase Start Time : 1994-01-25
Mission Phase Stop Time : 1994-01-25
Spacecraft Operations Type : ORBITER
LOW EARTH ORBIT
---------------
The Low Earth Orbit phase extended from the end of the
Launch phase until Clementine was spun up to 60 revolutions
per minute and the kick motor was fired, changing its
trajectory to a highly elliptical orbit which would encounter
the Moon. During this Low Earth Orbit phase on-board systems
were checked out and the spacecraft was three-axis stabilized.
Spacecraft Id : CLEM1
Target Name : MOON
Mission Phase Start Time : 1994-01-25
Mission Phase Stop Time : 1994-02-03
Spacecraft Operations Type : ORBITER
EARTH PHASING LOOP A
--------------------
Earth Phasing Loop A began at the end of the Low Earth Orbit
phase and lasted until Lunar Orbit Insertion. This phase
included two phasing loop orbits, the second of which allowed
encounter with the Moon.
Spacecraft Id : CLEM1
Target Name : MOON
Mission Phase Start Time : 1994-02-03
Mission Phase Stop Time : 1994-02-19
Spacecraft Operations Type : ORBITER
LUNAR ORBIT INSERTION
---------------------
The Lunar Orbit Insertion phase extended from the end of
Earth Phasing Loop A until the beginning of Lunar Mapping.
During this phase the spacecraft was placed in a lunar
orbit ranging from 400 to 2940 kilometers above the surface;
the orbit period was 5 hours. Lunar Orbit Insertion
occurred during revolution 0.
Spacecraft Id : CLEM1
Target Name : MOON
Mission Phase Start Time : 1994-02-19
Mission Phase Stop Time : 1994-02-19
Spacecraft Operations Type : ORBITER
LUNAR MAPPING
-------------
Lunar Mapping extended from the end of Lunar Orbit Insertion
until the beginning of Lunar Departure. During this phase
the instruments were checked out, sequences were developed
and tested for mapping operations, two complete cycles of
systematic mapping were completed, and the spacecraft was
prepared for leaving lunar orbit. The following sub-phases
can be defined for the Lunar Mapping phase:
Engineering Checkout and Operational Rehearsals (revolutions 1-31)
Systematic Mapping Cycle 1 (revolutions 32-164)
Systematic Mapping Cycle 2 (revolutions 165-300)
Post-Systematic Mapping (revolutions 301-350)
Spacecraft Id : CLEM1
Target Name : MOON
Mission Phase Start Time : 1994-02-19
Mission Phase Stop Time : 1994-05-03
Spacecraft Operations Type : ORBITER
LUNAR DEPARTURE
---------------
The Lunar Departure Phase extended from the completion
of Lunar Mapping until the beginning of Earth
Phasing Loop B. During this phase, the spacecraft was
removed from lunar orbit. The burn for Lunar Departure
began on 1994-05-04 at 03:24:15 and lasted 278 seconds;
it took place when the spacecraft was near 40 degrees N
latitude. This phase included parts of revolutions 350-351.
Spacecraft Id : CLEM1
Target Name : MOON
Mission Phase Start Time : 1994-05-03
Mission Phase Stop Time : 1994-05-04
Spacecraft Operations Type : ORBITER
EARTH PHASING LOOP B
--------------------
Earth Phasing Loop B extended from completion of the Lunar
Departure phase until loss of on-board attitude control
on 1994-05-07. During this phase the spacecraft was to
have been checked out in preparation for its flight
to Geographos.
Spacecraft Id : CLEM1
Target Name : MOON
Mission Phase Start Time : 1994-05-04
Mission Phase Stop Time : 1994-05-07
Spacecraft Operations Type : ORBITER
|
| MISSION_OBJECTIVES_SUMMARY |
The primary objective for DSPSE was demonstration of
high technology BMDO components. These included the four
advanced light weight 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.
To satisfy the constraints and goals outlined above, the
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.
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