EARLY HUMAN L2-FARSIDE MISSIONS
NEXT STEPS BEYOND LOW EARTH ORBIT
The L2-Farside mission is an intermediate step in a
series of increasingly challenging human exploration missions beyond low Earth Orbit using the Orion spacecraft.
The second Lagrange Point (L2) is a location where the
combined gravity of the Earth and Moon allows a spacecraft to be synchronized with the Moon in its orbit around
the Earth, so that the spacecraft appears to hover over the
Farside of the Moon.
Exploring the Farside
Key Messages
• Human missions to the L2 point over the unexplored Farside of the Moon can accomplish important scientific and exploration goals. From this
unique orbiting vantage point, astronauts could
control robots on the lunar surface to collect rock
samples or deploy a radio telescope.
• These missions are feasible by 2016-2018 using
Orion and either existing launch vehicles or a new
heavy lift launch vehicle. Orion is already designed with the advanced capabilities needed for
lunar flights, and can be easily modified to perform
this mission. It could be launched to the Moon on a
new heavy lift launch vehicle. Or, it could be
launched on an existing Delta IV rocket or Ares I
and boosted to the Moon using a Centaur upper
stage launched separately.
• Farside missions are early stepping stones to more
aggressive exploration. They provide practice
flights beyond low Earth Orbit which are needed
before attempting more difficult missions to asteroids. Astronauts would also demonstrate robot operations techniques that will later be used to explore Mars from orbit.
The Moon’s rotation causes one side to always face
Earth, and the other – the Farside – to always face away.
The Farside has been mapped from orbit, but no humans or
robots have ever landed there because the Moon blocks
direct radio contact with Earth. Extra relay satellites would
be needed.
There are two important science objectives on the
Farside, identified by the National Research Council as
high priority for future missions. The first is to return to
Earth multiple rock samples from the Moon’s South PoleAitken basin. This basin is one of the largest, deepest, and
oldest craters in the solar system. The cataclysmic asteroid
impact which created it excavated all the way through the
Moon’s crust, exposing inner layers of the Moon. By examining samples of these unusual rocks in labs on Earth we could learn about the internal structure of both the
Moon and the Earth, and what conditions may have been like on the early Earth when similar impacts were still occurring here, just before life first appeared.
The second objective is to spread a set of radio antennas on the Farside to create a low-frequency radio telescope. Because the Moon’s Farside is shielded from Earth’s radio noise, a radio telescope there could pick up signals that can’t be detected anywhere else. These include deeply redshifted radio signals from the early history of the
Universe before stars and galaxies formed, and signals that would help us understand phenomena on the Sun such as
solar flares.
Mission Plan
A mission to explore the Moon’s Farside can be performed using new or existing rockets and the configuration
of Orion which is designed for lunar missions. Since the Altair human lunar lander has been cancelled, a more affordable robotic lander would be developed instead.
The robotic lander and rover would be launched first on a slow but efficient trajectory to the Moon, to ensure
that the rover is on its way before risking the crew launch. Next, three astronauts would be launched in an Orion
spacecraft. If a heavy lift launch vehicle is developed, it would be capable of launching the crew directly towards
the Moon. If existing, smaller rockets are used instead, a more complex arrangement is needed. First, Orion would
be launched to Low Earth Orbit on a rocket such as a Delta IV Heavy or Ares I. Then, a modified Centaur upper
L1
ISS & Space Shuttle – 200 miles
Apollo – 249,000 miles, 12 days
L2 Farside Mission – 290,000 miles, 35 days
L2
stage would launch on a separate rocket. Orion would
dock to the Centaur stage in orbit, and the Centaur would
boost Orion towards the Moon.
Using either launch method, Orion would fly past
the Moon for a gravity slingshot maneuver towards the L2
point. Orion would use its propulsion system to enter a
halo orbit around the L2 point. From this vantage point
40,000 miles above the Farside of the Moon, Orion would
have continuous line-of-sight visibility to both the entire
Farside of the Moon, and the Earth. Astronauts could operate a rover on the lunar surface and stay in contact with
Mission Control at the same time. Astronauts would orbit
the L2 point for about two weeks – long enough to operate
a rover through the full length of a lunar day.
The Moon is close enough that rovers could be controlled from Earth using a simple relay satellite. However,
controlling the rovers from an orbiting spacecraft like
Orion is useful practice for Mars missions. As envisioned
by the Augustine Committee, the first human missions to
Mars may not attempt the difficult step of landing on the
surface, but may instead orbit Mars and control robot rovers on the surface. This may be more effective than controlling the rovers from Earth, because Mars is so far away
that the speed of light delay slows down operations. The
lunar L2-Farside missions will develop and practice operational methods for this type of joint human/robot exploration. In particular, they will address how much control and
decision making should be executed by the handful of ‘onsite’ astronauts in a spacecraft and how much will be done
by the larger staff with more resources at a more distant
mission control center.
Image credit: Lockheed Martin
Exploration Benefits
The L2-Farside mission is a logical early step beyond low Earth orbit in advance of longer trips to more
distant and challenging destinations like asteroids. Astronauts on an L2-Farside mission would travel 15% farther
from Earth than the Apollo astronauts did, and spend almost three times longer in deep space. Each flight would
prove out Orion’s life support systems for one-month duration missions before attempting a six month long asterImage credit: Lockheed Martin
oid mission. It would demonstrate the high speed reentry
capability needed for return from the Moon or deep space – 40 to 50% faster than reentry from low Earth Orbit. The
mission would measure astronauts’ radiation dose from cosmic rays and solar flares to verify that Orion provides
sufficient protection, as it is designed to do. Currently the medical effects of deep space radiation are not well understood, so a one-month mission would improve our understanding without exposing astronauts to excessive risk.
The L2-Farside mission also supports the development of key exploration technologies identified in the President’s FY2011 budget request. For example, the Centaur stage used for the Earth orbit departure maneuver uses
ultra-cold liquid oxygen and hydrogen propellants. Future human lunar landings and Mars missions would benefit
from the ability to store these cryogenic propellants for weeks or months, instead of the current state of the art of
several hours. The L2-Farside mission is an opportunity to demonstrate cryo-storage durations of a few days in an
operational scenario rather than a test.
NASA’s international partners are interested in the L2-Farside mission as a next step beyond the space station.
Other nations could build orbiting assets such as permanent habitat module at L2 to be visited by Orion, or could
provide complementary lunar surface hardware such as robotic landers, rovers, or science instruments.
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