AIAA 2006-5819
SpaceOps 2006 Conference
NASA Ground Network Support of the
Lunar Reconnaissance Orbiter
Stephen F. Currier * and Roger N. Clason †
Ground Network Project, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Marco M. Midon ‡
Microwave and Communication Systems Branch, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Bruce R. Schupler § and Michael L. Anderson **
Near Earth Networks Services, Honeywell Technology Solutions Inc, Lanham, MD 20706, USA
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This paper describes the Ground Network Project (GN) development and operational
approach to the support of the Lunar Reconnaissance Orbiter (LRO) Mission. The GN has
been assigned primary responsibility for fulfilling LRO’s communication requirements. In
order to support science data downlink, high accuracy ranging, telemetry, and command
requirements, the GN is implementing a new ground station, WS1, at White Sands, New
Mexico equipped with an 18-meter antenna, dual S/Ka-band receiver systems, redundant 2
KW S-band uplinks, and appropriate backend equipment. The design of this station is
derived from the NASA Solar Dynamics Observatory ground station. In addition, the GN is
procuring commercial S-band services to provide LRO coverage during periods when the
Moon is not in view of WS1, coordinating NASA Space Network activities for early mission
support, and facilitating support from the Deep Space Network for early mission and
contingency situations. During the science phase of the LRO mission the seven onboard
instruments will collect and store measurement data on the spacecraft recorder. Stored data
(science and housekeeping) will be transmitted at a nominal rate of 100 Mbps using a KaBand (26 GHz) link and received at WS1. Realtime housekeeping data will be transmitted at
S-band at nominal rates of 16 or 32 Kbps to either WS1 or the commercial S-band sites.
These same S-band antennas will also command LRO and close a high accuracy range and
range rate tracking loop with the spacecraft. Since the plane of the LRO orbit has a fixed
orientation in space, over the course of the lunar month the spacecraft will overfly the entire
lunar surface. This will also result in view periods from the Earth to the spacecraft which
vary from continuous visibility twice a month when the Earth-Moon line is perpendicular to
the plane of LRO’s orbit to alternating 56 minute view and eclipse periods when the EarthMoon line lies in the plane of the LRO orbit. The GN support scenario must accommodate
these variable viewing periods.
I.
Introduction
In June, 2005, the Lunar Reconnaissance Orbiter (LRO) Project and the Ground Network (GN) Project agreed
that the GN will organize and provide the Space Communications services necessary to successfully support the
LRO mission. LRO is scheduled for launch in October, 2008. LRO will be launched aboard an Evolved Expendable
Launch Vehicle (EELV) from the Eastern Test Range at the Kennedy Space Center (KSC). The launch vehicle will
inject LRO into a cis-lunar transfer orbit. After the lunar cruise, LRO will be required to perform a series of Lunar
Orbit Insertion maneuvers to capture into the commissioning orbit. After orbiter commissioning is complete,
additional orbit maneuvers will be performed to reach the mission lunar polar orbit at an altitude of 50 km.
*
Deputy Project Manager, Ground Network Project, NASA/GSFC/453
†
Project Manager, Ground Network Project, NASA/GSFC/453
‡
Electronic Engineer, Microwave and Communications Systems Branch, NASA/GSFC/567
§
Systems Engineer, NENS/HTSI
**
Systems Engineer, NENS/HTSI
1
American Institute of Aeronautics and Astronautics
This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.
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Once LRO is in the final mission orbit, the seven onboard instruments will begin to collect measurement data.
Data will be collected and stored on the spacecraft recorder. Data stored on the recorder will be dumped using the
Ka-Band system and received using a dedicated dual frequency (S/Ka) antenna located at White Sands, New
Mexico. Once the data is received on the ground, it is sent to the Mission Operations Center (MOC) for data
accounting and distribution to the seven Science Operations Centers (SOCs) for processing. Once the data
processing is complete, measurement data products are archived at the NASA Planetary Data System (PDS) for long
term storage and use.
Six of the instruments operate for the majority of the mission in the same operating mode. Periodic interruptions
are expected to the nominal measurement operations due to factors such as orbit maintenance, spacecraft momentum
management, instrument calibration maneuvers, lunar eclipses, and periodic yaw maneuvers.
These seven instruments aboard LRO are described below:
• Lunar Orbiter Laser Altimeter (LOLA): LOLA will determine the global topography of the lunar
surface at high resolution, measuring landing site slopes and searching for polar ice in shadow regions.
• Lunar Reconnaissance Orbiter Camera (LROC): LROC will acquire targeted images of the lunar
surface capable of resolving small-scale features that could be landing site hazards. LROC will also
produce wide-angle images of the lunar poles at multiple wavelengths to document the changing
illumination conditions and potential resources.
• Lunar Exploration Neutron Detector (LEND): LEND will map the flux of neutrons from the lunar
surface to search for evidence of water ice and provide measurements of the space radiation
environment thereby identifying potential resources and hazards for future human exploration.
• Diviner Lunar Radiometer Experiment: Diviner will map the temperature of the entire lunar surface
at 300-meter horizontal scales to identify cold-traps and potential ice deposits.
• Lyman-Alpha Mapping Project (LAMP): LAMP will observe the entire lunar surface in the far
ultraviolet. LAMP will search for surface ice and frost in the Polar Regions and provide images of
permanently shadowed regions which are illuminated only by starlight.
• Cosmic Ray Telescope for Effects of Radiation (CRaTER): CRaTER will investigate the effect of
galactic cosmic rays on tissue-equivalent plastics as a constraint on models of biological response to
background space radiation.
• Mini-RF: The Mini-RF is a technology demonstration X-band and S-band Synthetic Aperture Radar.
II.
Ground Network Support Approach
The cornerstone strategy for establishing an effective and cost efficient ground based tracking solution for LRO
was to maximize the direct reuse of engineering designs accomplished for earlier missions. The Solar Dynamics
Observatory (SDO) Project is a NASA Sun-Earth Connection mission that was at the Critical Design Review phase
of ground station development when the GN support strategy was being developed. SDO shares very similar
telemetry system design and data rate requirements with LRO. As a result, much of the SDO ground station design
was reused in the GN design for LRO services. Additional contractual synergies between the SDO and LRO efforts
were also realized. The SDO ground system team had in place an existing contract with an antenna manufacturer for
the construction and installation at the NASA White Sands Complex in New Mexico of a redundant pair of tracking
antennas. The decision was made to leverage this contract in two ways. The first facet was an increase in the size of
the already planned two SDO antennas from 9-meter to 18-meter diameter and the second facet was the addition of a
third 18-meter antenna for GN support of LRO. This procurement plan for three nearly identical antenna systems
includes an evolutionary vision for establishing future array configurations in order to boost gain performance over
that of a single antenna.
Two primary design requirement differences exist between the SDO and LRO missions. The SDO mission space
segment consists of a geosynchronous satellite which is dedicated to solar observation. Mission data capture
requirements led to the necessity for two dedicated antennas for the duration of the SDO mission. As a result, the
SDO antennas will not require a multimission scheduling function. The SDO mission will operate the two SDO
dedicated 18-meter antennas remotely from the SDO Mission Operations Control Center which is located over 2,000
miles away from the antenna tracking station. In contrast, the GN antenna is planned for multimission utilization and
will require a robust, even if not initially sophisticated, scheduling capability or interface. The current design
includes utilization of the existing GN scheduling system, WOTIS.
The dual frequency GN antenna, designated WS1, is envisioned to support multiple missions with the LRO
mission being the first officially documented requirement. Although the LRO mission is the first to establish a
Project Service Level Agreement for support on WS1, it may not be the first mission to receive support from this
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antenna. LRO is planned for an October, 2008 launch, and WS1 is scheduled to be installed by August, 2007.
Several other on-orbit missions may, therefore, receive GN services from WS1 prior to the LRO mission. The GN
plans to operate WS1 via remote control using a system located in a different part of the White Sands Complex. The
remote monitor and control capability represents the initial approach to operations of the WS1 antenna system. The
longer term evolutionary vision includes a more robust monitor and control center serving a worldwide network of
antennas.
Additional tracking, commanding, and housekeeping data requirements of LRO necessitated the use of
additional S-band only stations in the LRO support solution. The GN is providing this additional S-band support
through the use of a commercial service provider. Tone ranging and Doppler tracking are required for at least 30
minutes of every visible pass the LRO spacecraft makes with respect to the Earth. A coverage solution was devised
and refined through a series of coverage analyses and trade studies. The final solution includes four additional Sband only tracking sites located worldwide. The tracking stations were selected based on their S-band capabilities,
viewing coverage of the Moon, and availability. These non-NASA tracking sites along with the NASA-owned 18meter GN antenna will round out the nominal operation service compliment for the LRO mission. The Deep Space
Network (DSN) is integrated into the solution space for launch, early trajectory, and contingency operations. The
larger aperture tracking systems and higher power EIRP capabilities of the DSN allow the DSN to close the RF link
to the LRO through the omni-directional antenna on the spacecraft even with unfavorable antenna aspects. The
NASA Space Network (SN) is also integrated into the LRO support concept to provide coverage during the critical
portion of the mission after launch and prior to the acquisition of the spacecraft by the first ground station.
One of the primary objectives of the LRO mission is to establish a highly accurate gravity model of the moon.
In order to aid in the accomplishment of this goal, a more precise ranging solution than can be provided by the RF
ranging system is also desired. The GN will provide a ground based laser tracking service for this requirement.
The total compliment of services integrated by the GN to support the LRO mission include the S and Ka-band
services from the NASA owned 18-meter GN antenna, the S-band commercial tracking services, the DSN launch,
early trajectory, contingency services, the SN early mission services, and the ground based laser tracking service.
The intent of this paper, however, is to focus on the S and Ka-band tracking services of the NASA owned 18-meter
antenna and the reuse of existing engineering design work in the implementation of this solution element.
III.
Ground Station Design
Figure 1 provides a high level conceptual block diagram of the WS1 ground station as it interfaces with internal
and external functions and organizations. The WS1 18-meter antenna will be located at the NASA White Sands
Complex near Las Cruces, New Mexico. The low humidity and precipitation characteristics of this site will be
beneficial for the RF performance of the high data rate Ka-band downlink. WS1 will receive in both S and Ka-band
simultaneously and have the capability to autotrack in each band. WS1 will have an S-band transmit capability in
order to perform tone ranging, Doppler tracking, and spacecraft commanding. In Figure 1 WS1 is defined by the
dark blue blocks, which include the antenna subsystem, the signal processing subsystem and the monitor and control
subsystem. These three WS1 blocks will be located at the same facility. The remaining subsystem blocks that are
also located at the same facility include the common time and frequency subsystem (CTFS), the data services
management center (DSMC), and the LRO mission unique equipment. The CTFS is part of the existing
instrumentation of the White Sands Complex and will be shared as a cost saving approach. Use of the CTFS by both
the WS1 antenna and other antennas at the site will facilitate possible future antenna arraying efforts. The CTFS
exceeds the accuracy required for the tone ranging and Doppler tracking desired. The DSMC includes the GN
scheduling function. The DSMC organization will operate the WOTIS in order to generate and deliver scheduling
and acquisition data products to the WS1 antenna system. The LRO mission unique equipment will perform low
levels of data processing and handling operations of the high rate Ka-band data. The initial design includes
interfaces to two facilities located over two thousand miles away. The first facility is the flight customer Mission
Operations Center (MOC) and the second facility is the Flight Dynamics Facility (FDF). Future design includes a
vision of a remote operations center that performs the monitor and control function for multiple WS1 class antennas
located worldwide. The GN will provide to the MOC real-time S-band telemetry data, monitor and control status of
the WS1 antenna system, tone ranging and Doppler tracking data products, and data from the Ka-band downlink.
The MOC will send command data strings back to the WS1 and scheduling request products back to the DSMC. The
GN will deliver tracking data products to the FDF. The FDF will provide acquisition data products back to the
DSMC.
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WSC
Common Time and
Frequency
Subsystem
(CTFS)
TIMING
REFERENCE
TIMING
REFERENCE
Data Services
Management
Center
(DSMC)
ACQUISITION
DATA
ACQUISITION DATA
Key:
WS1
Future
External
REQUIREMENTS
SCHEDULE
DATA
Remote
Operations Center
TIMING
REFERENCE
CONTROL & STATUS
CONTROL
& STATUS
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Antenna Subsystem
(AS)
Monitor & Control
Subsystem
(MCS)
Flight Dynamics
Facility
(FDF)
CONTROL
& STATUS
TRACKING DATA
S-BAND RF
S-BAND RF
Ka-BAND IF
Mission Unique
Equipment
(MUE)
STATION STATUS
Ka-BAND DATA
SCIENCE DATA
Signal Processing
Subsystem
(SPS)
COMMANDS & ACQUISITION DATA
TELEMETRY
TRACKING DATA
WS1
Mission Operations
Center
(MOC)
GSFC
Figure 1. The WS1 Ground Station Features Partitioning of Services Into Clearly Defined Modules
Of the three WS1 blocks, two are complete reuse of engineering designs accomplished by the SDO Project. The
monitor and control subsystem will be a design different from that of the SDO mission. The monitor and control
subsystem architecture will also leverage existing engineering design from other networks. The commercially
available monitor and control engine selected for reuse on the WS1 system has earlier versions of the same product
operating existing NASA antennas, NOAA antennas, and is currently in development on a DoD network
modernization project. The selection of the monitor and control system was based on a number of factors. Direct
reuse of the SDO monitor and control design did not appear well suited due to the significant difference in the
operating concepts of the antenna systems. The SDO operation concept includes operating the antenna subsystem
from the SDO Mission Operations Control Center. The GN operations concept will employ significant levels of
automation and perform many additional functions locally at the antenna facility location. The SDO mission also
models a pair of dedicated antennas in order to meet the challenging data capture and recovery requirements of the
mission. Because the SDO antennas are dedicated to the SDO project and will operate in a simultaneous best source
select and hot backup configuration, scheduling of the antennas is not a factor. The SDO spacecraft will be placed in
a geosynchronous orbit and the SDO antennas will track the SDO spacecraft continuously. Therefore, the scheduling
function is not required in the SDO application.
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10 MHz
10 MHz
Media Converters
IRIG B
S-BAND RF
2025-2120 MHz
BACKUP RF / IF to / from SDO
S-BAND XMIT /
TEST INJ
2025-2120MHz
RECEIVE Ka-BAND
RECEIVE / TRANSMIT S-BAND
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S-BAND RF
2025-2120MHz
S-BAND RHCP
IF 70 MHz
S-BAND RHCP
2200-2300 MHz
S-BAND/RHCP
2200-2300MHz
S-BAND/RHCP
2200-2300MHz
S-BAND/LHCP
2200-2300MHz
S-BAND/LHCP
2200-2300MHz
TO-26
Provided
Fiber Optic
Assembly
Tx/Rx
RF
Distribution
Assembly
&
Switch
Converter
Assembly
S-BAND RHCP
IF 70 MHz
S-BAND LHCP
IF 70 MHz
Ka-BAND IF
720 MHz
Ka-BAND IF
720 MHz
Ka-BAND IF 720 MHz
Ka-BAND IF 720 MHz
Ka-BAND TEST
INJECT IF 720 MHz
Ka-BAND
TEST INJECT IF
720 MHz
Ka-BAND
TEST INJECT IF
720 MHz
Ka-BAND IF 720 MHz
Ka-BAND IF 720 MHz
Ka-BAND TEST
INJECT IF 720 MHz
TO-69
Future
External
High Data
Rate
Receiver
(HDR)
Antenna
Control &
Monitoring
Antenna Control
Computer
(p/o Ka-Band / S-Band
Antenna Assembly)
Monitor &
Control
Subsystem
(MCS)
10 MHz
IRIG B
IRIG B
Receive
Range
Command
Processor
Assembly
(RRCP)
CTFS
WSC
Mission
Operations
Center
(MOC)
GSFC
Data
Storage
WS1
Media Converters
SDO
Derived
S-BAND IF
70 MHz
S-BAND LHCP
2200-2300 MHz
Ka-BAND IF
720 MHz
(p/o Ka-Band / S-Band
Antenna Assembly)
S-BAND LHCP
IF 70 MHz
S-BAND LHCP
2200-2300 MHz
Ka-BAND IF
720 MHz
Antenna
Control &
Monitoring
Key:
10 MHz
S-BAND IF
70 MHz
S-BAND RF
2025-2120 MHz
S-BAND RHCP
2200-2300 MHz
Ka-Band /
S-Band
Antenna
Assembly
Timing
Distribution
Assembly
IRIG B
(p/o Ka-Band / S-Band
Antenna Assembly)
Weather
Station
Mission
Unique
Processor
Equipment
WSC
Remote
Monitor
and
Control
Figure 2. The WS1 Station Design Features Major Reuse of Existing Modern Design and Utilizes Existing
Contract Vehicles to Speed Delivery Time and Reduce Cost
Figure 2 illustrates additional detail of the backend electronics included in the GN antenna design. The backend
systems of WS1 are being developed under a contract task number sixty-nine, which is represented by TO-69 and
shaded in blue in Figure 2. The antenna system components, which are developed under contract task number
twenty-six are represented by TO-26 and shaded in yellow in Figure 2. The backend ground station electronics that
are direct reuse of SDO design are represented in Figure 2 by blue shading with a black corner in the diagram
blocks. Equipment and facilities outside of the GN organization are represented by gray shaded blocks in Figure 2.
Effective reuse of design is clearly demonstrated in Figure 2 by the abundance of yellow boxes and blue shaded
boxes with black corner shading. The only subsystem areas that will deviate from direct provision or design reuse
are the monitor and control subsystem, the data storage subsystem and the weather station, the last item not being
required by the SDO mission.
Figure 3 provides an elevation view of the GN 18-meter Cassegrain parabolic reflecting antenna. The antenna
will operate at Ka and S-band frequencies. The feeds and associated electronics are located at the Cassegrain focus,
with the Ka-band feed offset by using a dichroic kickplate arrangement. The antenna surface and mount are
designed to be able to track at Ka-band in a sustained wind of 72 km/hr and survive in a wind of 200 km/hr.
The antenna surfaces and mounts for all three 18-meter antennas that will be installed at White Sands are
currently under construction by the vendor. Figure 4 shows the antenna backup structure. Note the use of the curved
subreflector support arms for increased mechanical stability. In the foreground of Figure 5 is a view of the riser of
the 18-meter antenna. The diameter of this riser may be contrasted with the riser of a 13-meter antenna which is
under construction in the background of this picture.
Figure 6 illustrates the use of the dichroic kickplate for the Ka-band frequencies. Because of the arrangement of
the antenna optics, the S-band signal undergoes two reflections (from the primary reflector and the solid
subreflector) while the Ka-band signal undergoes three reflections (from the primary reflector, the solid subreflector,
and the dichroic subreflector). Consequently, the polarization of the S-band feed is the same as that of the antenna
while the Ka-band feed polarization is opposite to that of the antenna. Table 1 contains a listing of selected key
characteristics of the WS1 antenna system.
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Figure 3. The WS1 Antenna Design Provides Dual Frequency Operations Using a Commercially Available
Antenna Design
Figure 4. Antenna Reflector Backup Structure Under
Construction at the Vendor in April, 2006
Figure 5. Antenna Riser for the 18m
Antenna Under Construction at the
Vendor in April, 2006
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Table 1. Key Characteristics of the WS1 Antenna System
Parameter
Value
Main reflector diameter
18.3 meters
S-band receive frequency range
2200 to 2300 MHz
S-band transmit frequency range
2025 to 2120 MHz
Ka-band receive frequency range
25.5 to 27.0 GHz
S-band G/T (See Note 1)
28.8 dB/K
Ka-band G/T (See Note 2)
45 dB/K
S-band EIRP
79 dBW
Maximum slew and tracking rate
2o per second on each axis
Azimuth range
+400 o
Elevation range
0o to +180o
Mount type
Elevation over azimuth
Note 1 - S-band G/T value is for clear sky and 5° elevation angle.
Note 2 - Ka-band G/T is for clear sky and 10° elevation angle.
Figure 6. The Use of a Ka-band Dichroic
Kickplate Enables the WS1 Antenna to Meet
the Mechanical Stability Requirements for High
Accuracy Tracking
IV.
Operational Scenarios
The launch and initial lunar orbit maneuver phases of the LRO mission will involve support from the NASA
Space Network, the DSN, and the commercial S-band stations in addition to WS1. Once the spacecraft has safely
reached its lunar orbit, primary support will be through WS1 and the commercial S-band stations with the DSN
available for contingency support, if required.
LRO’s science lunar orbit is a polar orbit at a nominal altitude of 50 km with a corresponding orbital period of
113 minutes. Depending on the orientation of the Earth and the plane of LRO’s orbit, visibility of LRO from the
Earth ranges from continuous to alternating 56.5 minute periods of visibility and occultation by the Moon. (See
Figure 7 for an illustration of the geometry of the LRO orbit.) Due to mechanical limitations on the pointing range of
the LRO High Gain Antenna (HGA) the maximum Ka-band contact period is limited to 56 minutes per orbit even
during periods of full visibility of LRO from the Earth. During periods when LRO cannot point its HGA at the Earth
and is not occulted by the Moon communication with the spacecraft is possible through the omni antenna from Earth
stations with sufficient G/T and EIRP.
In addition to interruptions in communication caused by lunar occultations, there are several brief periods per
year when the Moon and Sun are close together in the sky as seen from the Earth. The intense interference from the
Sun during these periods will make communication from LRO to the ground impossible. During calendar year 2009,
the Moon and Sun appear to be within 3o of each other as seen from all available ground stations for approximately
30 hours divided into 5 periods ranging from 2 to 11 hours in length.
The support plan for LRO has the WS1 station providing coverage for all LRO passes that are visible from the
White Sands site with the commercial S-band stations providing coverage for the remaining passes. The WS1
antenna will provide coverage for approximately 45% of all LRO passes with the commercial sites covering the
remaining 55%. The visibility of the Moon above 5o elevation as seen from the ensemble of WS1 and the four
commercial S-band stations is shown in Figure 8. As can be seen from this figure, coverage of the Moon is available
from more than one station at a time nearly 82% of the time. As noted above, WS1 will provide coverage for all
passes visible from the site. The WS1 S-band coverage limits are shown in Figure 9. The small zone of noncoverage
in Figure 8 off the east coast of South America at the southern limit of the Moon’s orbit spans a total of
approximately 30 hours per year and is an artifact of the 5o elevation limit. Lowering the elevation limit slightly at
Weilheim and WS1 eliminates this coverage gap.
The corresponding WS1 coverage limits for Ka-band with an elevation limit of 10o are shown in Figure 10. With
this elevation limit, WS1 can provide Ka-band coverage for approximately 41% of all LRO passes.
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Beta 0º
Yaw Maneuver
Eclipse Season
Beta 76.4°
Beta 76.4°
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Earth
Beta 90º
Full Sun
(~1 month)
~1 month
Orbit
Full Earth View
(~2 days)
Moon
113 Mins
Full Sun
(~1 month)
Beta 90º
Full Earth View
(~2 days)
Beta 76.4°
Beta 76.4°
Sun
Eclipse Season
1 Year
Yaw Maneuver
Beta 0º
Figure 7. The Changing Geometry of the Moon, Earth, and Sun Provides Variable LRO Contact
Periods
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Figure 8. Visibility of the Moon from the Ensemble of S-band Stations with a 5 Degree Elevation Limit
Figure 9. S-band Visibility of the Moon from WS1 with a 5 Degree Elevation Limit
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Figure 10.
Ka-band Visibility of the Moon from WS1 with a 10 Degree Elevation Limit
Figure 11.
LRO’s Contacts With Ground Stations Consist of 12 HGA Viewing Periods per Day
During the WS1 passes, realtime S-band housekeeping telemetry reception, S-band commanding, and S-band
range and range rate measurements will be performed in addition to Ka-band data downloads from the spacecraft
recorder. Given the nominal LRO data volume of 573 Gbits per day, the 100 Mbits / second LRO Ka-band downlink
rate, and 4 WS1 passes per day, the Ka-band downlink utilization is approximately 61% of capacity.
Figure 11 illustrates the notional daily ground contact plan for LRO including contacts from WS1 (the passes
shown as S-band and Ka-band), the commercial S-band stations, and the laser tracking station. In addition, the
transfer of data received on the Ka-band downlink to the MOC is also shown. The S-band data from both WS1 and
the commercial stations is delivered to the MOC in near realtime.
Figure 12 displays the Ka-band downlink strategy. The first two passes of a given LRO view period from WS1
are fully utilized to dump Ka-band from the spacecraft recorder. At the completion of the second pass, the spacecraft
recorder has been almost, but not quite, emptied. The third pass completes the download of the data that was in the
recorder at the start of the view period plus the data that has been recorded since the view period started while the
fourth pass downloads the data that was collected between the end of the download during the third pass and the
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start of the fourth pass. This strategy permits LRO to maximize the storage available on the recorder as the
spacecraft passes out of view of WS1.
Minutes
D/L Time Used
50
45
40
35
30
25
20
15
10
5
0
45
34.3
36.4
10.7
8.6
3
4
45
1
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D/L Time Remaining
2
Daily WS1 Contact Number
Figure 12.
Nominal LRO Ka-band Downlink Utilization
V.
Conclusion
The development of the 18-meter S and Ka-band autotracking antenna system that will support the LRO and
many other NASA and presumably non-NASA missions has effectively employed a strategy of reuse of design and
existing technology in order to reduce cost and development schedule. The synergy established by standardizing the
antenna designs between SDO and the GN provides several attractive benefits. The training, operations,
maintenance, sustaining engineering, and logistics support required for each antenna system can now be shared,
thereby reducing costs overall. Contingency operations procedures are currently in development as a result of the
similar design and collocation of the antenna systems. The suite of three apertures collocated provides opportunity
for future array technology demonstration and eventual mission support. The result of these synergies includes
increased operability and reduced total lifecycle cost and development schedule.
Acknowledgments
The authors wish to thank the Lunar Reconnaissance Orbiter Project for supporting financially and maintaining
confidence in this service approach, and the Ground Network and Solar Dynamics Observatory project management
for endorsing this engineering and operations collaboration.
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