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Description
As part of the President's Space Exploration Vision
outlined in January 2004, human presence will once again extend to the Moon. Lunar Communication is an
important aspect of manned and unmanned missions to the moon. Since
we do not yet have mission control set up on the lunar surface, we need to maintain
communication between our astronauts and instruments on the moon and the Earth. Continuous
direct to Earth communication is not feasible from the far side of the moon, a prime potential
location for astronomical observatories. Depending on the landing site choice, continuous and
direct communications between the astronauts and the Earth might not be possible on the near side
of the moon as well. There is slowly becoming a recognition of the need to have a system
set up that provides continuous Earth/Lunar communication and in some mission profiles,
Lunar based navigation for the human and robotic explorers.
Depending on the communication requirements that are needed to
support a human lunar base, communication links may be needed between the lunar base, the lunar
surface, moving assets such as rovers, the spacecraft in transport, the lunar near side, the
lunar far side, and the Earth. There are two main Earth to the Moon communication
architecture options to explore: Earth-region data relay satellites and Earth ground stations.
Potential, but impractical, direct data relay satellite candidates
are direct from the Moon to Low
earth orbit (LEO)  or
Medium earth orbit (MEO) options. These options become impractical when the extreme power requirements
to cover the communication distance as well as the short orbital period are taken
into account.
Geosynchronous orbit (GEO) satellites would be better options because of the continuous ground link this
orbit provides. An example of a geosynchronous architecture is the
tracking data relay satellite (TDRS). The TDRS system currently has four satellites in geosynchronous orbit and
two Earth terminals located in White Sands, New
Mexico. TDRS is currently designed to provide communications and tracking service to
space-based users in the region between LEO and GEO.
Another potential relay satellite option would use the Earth-Moon L1 or L2
Lagrangian points . A satellite stationed at the L2 point could provide coverage of the
lunar far side. In order to transmit to the Earth, the L2 satellite would need to be
placed in a
halo orbit sufficiently large enough to allow it to get a direct line to Earth
and not be obstructed by the moon. A data relay satellite could also be placed at the
Earth-Moon L1 point. Additionally, depending on the communication and navigation coverage
requirements in the Lunar mission architecture of the lunar surface, a lunar
orbiting relay satellite constellation might be considered as a relay link. The downside to
any relay satellite option is launch vehicle , satellite development and lifecycle cost.
The second architecture options for the Earth-region communication
link is direct from the Moon to Earth ground stations. An example of a ground
station architecture is the Deep Space Network (DSN).
The three
multi-antenna DSN complexes are positioned in
Goldstone California,
Canberra Australia, and
Madrid, Spain.
Depending on the mission requirements, a series of communication
architecture options (relay satellites, earth based assets, and earth orbiting assets)
will need to be studied. Cost, ability to perform the mission, and technical feasibility will
all be factors in weighing lunar communication architecture options.
7820 Participation
Starting with the 2001 NASA initiative known as “Beacon”, an
agency-wide project whose function was to begin developing architecture plans to unite the
communications infrastructure within NASA, 7820/ Systems Analysis Branch
has been involved in the mission architecture facet of Lunar Communications Studies.
Chartered as a mission and systems analysis group, we have been and
still are responsible for laying out lunar communications options involving orbital assets,
both existing and new. For “Beacon”, we researched current state of the art ELV
(Expendable Launch Vehicle) performance data. Based on this data, trajectory analyses were done
in order to establish payload capabilities to Lunar orbit or Earth-Moon Lagrange points.
These payload capabilities allowed us to design orbital constellation configurations that
provide full coverage for lunar communications and navigation. In the future, the branch plans
to be involved in both determining requirements for lunar communications and navigation
as well as participating in architecture studies whose role will be to generate concepts to
meet those requirements.
Other Links of Interest to Lunar Communication
Points of Contact
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7820
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GRC Resident Expert
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HTML Contributions
- Summer Interns '04
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