orbits of the Moon of 152° and 169°. Clementine was inserted into an eccentric, five hour
orbit, with a mean periapse altitude of 415 km.
The data consist of 2-way and 3-way S-Band Doppler tracking. These data types are
described by Moyer [1971]. The Lunar Orbiters were tracked by the antennae of the Deep
Space Network (DSN), principally stations 12,41,61, and 62. The data from the Lunar
Orbiters consist mostly of data averaged over 60 seconds, and have a noise ranging from
0.35 to 5 mm/s, depending on the arc of data. The Apollo subsatellites were tracked by the
Manned Space Flight Network (MSFN), a network of ground stations created to support
tracking of the Apollo spacecraft in orbit about the Moon. These data are also S-Band and
have characteristics similar to the data from the Lunar Orbiters. The Clementine data
consist of S-Band tracking from the 26 and 34 meter antennae of the DSN, as well as
additional tracking provided by a 30 meter antenna operated by the Naval Research
Laboratory (NRL) in Southern Maryland. The Clementine DSN data have a noise of 0.25
mm/s, averaged over 10 seconds, whereas the NRL station has a data noise of 2.5 mm/s
averaged over the same time interval.
The data from the Lunar Orbiters are heavily contaminated by attitude maneuvers. The
Lunar Orbiters were three axis stabilized spacecraft Each satellite had a circular bus, with
a height of 2.08 m, a width from tip to tip across the solar panels of 3.78 m, and a mass
of 250 to 300 kg in lunar orbit. The Lunar Orbiters possessed an attitude control system
that was uncoupled in both yaw and pitch [Konopliv et al., 1993]. Thus, almost every
time the satellites changed their orientation, a spurious acceleration was imparted to the
spacecraft orbit Fortunately, the time - if not the magnitude of the attitude maneuver - has
been preserved. It is possible to account for these orbit perturbations by solving for
radial, transverse, and cross track accelerations at the times of maneuvers. Nevertheless,
during the primary or photographic missions of the Lunar Orbiters, corresponding to the
first weeks in lunar orbit, as many as 14 maneuvers occurred per day.
Not by
coincidence, the densest tracking is also available only at this time. Tracking of the Lunar
Orbiters was sparser during the extended missions when attitude maneuvers were less
frequent. During the primary missions, we limited data arcs to no longer than one day,
and combined maneuvers that occurred close together in time.
Clementine entered lunar orbit on February 19, 1994, and remained at the Moon until its
departure for the asteroid 1620 Geographos on May 4, 1994 [Nozette et al., 1994]. The
satellite was placed in an elliptical orbit, with periapse at 30° S during the first month in
lunar orbit, and at 30° N during the second month in lunar orbit. A proposal to lower
periapse height to 100 km at the end of lunar mapping (April 22, 1994) to obtain higher
resolution data over the northwest near side was rejected because of its impact on remaining
plans for the Geographos and another asteroid encounter.
Because of the lunar geometric librations and the effect of parallax, it is possible to track
spacecraft beyond the edges of the lunar limb. We can obtain tracking data to
approximately ± 120° in longitude, where 0° longitude is the center of the lunar near side.
Likewise, tracking is also possible over the lunar poles to about 60° to 70° N or S. In the
absence of any satellite to satellite tracking - which will hopefully be rectified by the
proposed European mission MORO [Chicarro et al., 1994], we have direct tracking over
60 percent of the lunar surface.
Of the Apollo 15 sub satellite data used in this study, as discussed by Konopliv et al.
[1993], we have access to only a portion of the total data acquired: some 3 1/2 months
from September to December 1971, including two gravity campaigns, and several weeks of
intermittent tracking (mostly two hour passes) from April through May 1972. The
178
orbit, with a mean periapse altitude of 415 km.
The data consist of 2-way and 3-way S-Band Doppler tracking. These data types are
described by Moyer [1971]. The Lunar Orbiters were tracked by the antennae of the Deep
Space Network (DSN), principally stations 12,41,61, and 62. The data from the Lunar
Orbiters consist mostly of data averaged over 60 seconds, and have a noise ranging from
0.35 to 5 mm/s, depending on the arc of data. The Apollo subsatellites were tracked by the
Manned Space Flight Network (MSFN), a network of ground stations created to support
tracking of the Apollo spacecraft in orbit about the Moon. These data are also S-Band and
have characteristics similar to the data from the Lunar Orbiters. The Clementine data
consist of S-Band tracking from the 26 and 34 meter antennae of the DSN, as well as
additional tracking provided by a 30 meter antenna operated by the Naval Research
Laboratory (NRL) in Southern Maryland. The Clementine DSN data have a noise of 0.25
mm/s, averaged over 10 seconds, whereas the NRL station has a data noise of 2.5 mm/s
averaged over the same time interval.
The data from the Lunar Orbiters are heavily contaminated by attitude maneuvers. The
Lunar Orbiters were three axis stabilized spacecraft Each satellite had a circular bus, with
a height of 2.08 m, a width from tip to tip across the solar panels of 3.78 m, and a mass
of 250 to 300 kg in lunar orbit. The Lunar Orbiters possessed an attitude control system
that was uncoupled in both yaw and pitch [Konopliv et al., 1993]. Thus, almost every
time the satellites changed their orientation, a spurious acceleration was imparted to the
spacecraft orbit Fortunately, the time - if not the magnitude of the attitude maneuver - has
been preserved. It is possible to account for these orbit perturbations by solving for
radial, transverse, and cross track accelerations at the times of maneuvers. Nevertheless,
during the primary or photographic missions of the Lunar Orbiters, corresponding to the
first weeks in lunar orbit, as many as 14 maneuvers occurred per day.
Not by
coincidence, the densest tracking is also available only at this time. Tracking of the Lunar
Orbiters was sparser during the extended missions when attitude maneuvers were less
frequent. During the primary missions, we limited data arcs to no longer than one day,
and combined maneuvers that occurred close together in time.
Clementine entered lunar orbit on February 19, 1994, and remained at the Moon until its
departure for the asteroid 1620 Geographos on May 4, 1994 [Nozette et al., 1994]. The
satellite was placed in an elliptical orbit, with periapse at 30° S during the first month in
lunar orbit, and at 30° N during the second month in lunar orbit. A proposal to lower
periapse height to 100 km at the end of lunar mapping (April 22, 1994) to obtain higher
resolution data over the northwest near side was rejected because of its impact on remaining
plans for the Geographos and another asteroid encounter.
Because of the lunar geometric librations and the effect of parallax, it is possible to track
spacecraft beyond the edges of the lunar limb. We can obtain tracking data to
approximately ± 120° in longitude, where 0° longitude is the center of the lunar near side.
Likewise, tracking is also possible over the lunar poles to about 60° to 70° N or S. In the
absence of any satellite to satellite tracking - which will hopefully be rectified by the
proposed European mission MORO [Chicarro et al., 1994], we have direct tracking over
60 percent of the lunar surface.
Of the Apollo 15 sub satellite data used in this study, as discussed by Konopliv et al.
[1993], we have access to only a portion of the total data acquired: some 3 1/2 months
from September to December 1971, including two gravity campaigns, and several weeks of
intermittent tracking (mostly two hour passes) from April through May 1972. The
178