PDS_VERSION_ID = PDS3
RECORD_TYPE = FIXED_LENGTH
RECORD_BYTES = 80
SPACECRAFT_NAME = "CLEMENTINE 1"
TARGET_NAME = {EARTH, MOON, SKY}
OBJECT = TEXT
INTERCHANGE_FORMAT = ASCII
PUBLICATION_DATE = 1994-10-1
NOTE = "TIMELINES FOR CLEMENTINE SPACECRAFT"
END_OBJECT = TEXT
END
CLEMENTINE ORBIT TIMELINES
The Clementine orbit timeline information was added as part of the
volume series just when production began. Because of the late
addition of the files in this directory, they do not conform to PDS
standards. Because these files are supplemental to the overall
requirements of the volume design, it was decided that PDS
requirements were not needed for these files. The timeline data,
provided in a PDS compliant format, will be made available through
the SPICE system on the Clementine ancillary data CD-ROM series.
The actual spacecraft timelines are included for each of the orbits
contained in this CD. They are in Microsoft Excel for Windows format.
The general form of the file name scheme is as follows:
TLLUNxxx.XLS - Lunar orbit timeline for revolution 'xxx'
TLEPAxxx.XLS - Earth phasing loop A timeline for dump 'xxx'
TLEPBxxx.XLS - Earth phasing loop B timeline for dump 'xxx'
TLLEOxxx.XLS - Low Earth Orbit timeline for dump 'xxx'
These timelines are based on the predicted timelines that were used
to write the spacecraft command sequence scripts that were uploaded
to the spacecraft for each orbit. Those predicted timelines were
updated with the definitive trajectory of the spacecraft as
determined by post-flight orbit determination. The timelines were
then compared with the actual command scripts and console logs to
ensure that they show what really happened instead of what was
planned. The image summaries for the orbit were used to determine
when images (during the orbit) were being taken for each camera and
whether or not they were compressed, uncompressed, color, etc. It
should be noted that although care was taken in developing these
timelines for the CDs, some errors and omissions have occurred,
partly because of incomplete or contradictory records.
The timeline is a listing of significant events (orbital, spacecraft,
and ground station) during the orbit as a function of time. It should
be noted that the Clementine lunar orbits are numbered by convenience
and not according to standard orbital dynamics practice. According to
standard practice, especially with Earth-orbiting satellites, the
orbit number increments when the satellite passes the ascending node.
On the Clementine mission, due to the South to North polar mapping
orbit, the ascending node occurred at the equator on the sunlit side
of the Moon, right in the middle of mapping. This means that
following standard practice, either the contiguous set of mapping
images (or swath) would have to be split up between two orbits, which
was unacceptable to the Clementine team, or the archived data would
have to reflect both orbit numbers, e.g., Orbit 1/2. Initially this
latter method was used. However, due to simplicity and convenience,
the second orbit number was soon dropped and each orbit timeline and
data are numbered by the orbit number at the time that mapping
started, as the spacecraft crossed the South Pole. This also
corresponded with the design of the timelines, because the break
point for starting and ending each timeline naturally occurred during
the long data dump period of the orbit, where there were usually no
command scripts active. The timelines were thus designed to start and
stop at aposelene (apoapsis), which is a fixed orbital point in the
middle of the data dump period. It is from this point that the
"Orbital Time" shown in the timelines is calculated.
The timelines use the terms "periselene" for the periapsis of the
elliptical lunar orbit, and "aposelene" for the apoapsis of the
elliptical lunar orbit. These points in a lunar orbit are also
sometimes referred to as the "perilune" and "apolune" respectively.
For definitions of the acronyms and terms used in the timelines,
please refer to the ancillary CD.