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Flight Plans Newsletter

23. Return to the Moon

by Gus Posey, Education Department, The Museum of Flight An Earth Departure Stage, docked to the Crew Exploration Vehicle, fires its engine to leave Earth’s orbit. -Image courtesy of NASA/John Frassanito and Associates.

Between 1969 and 1972, NASA sent 12 men to the surface of the moon. Despite the overwhelming success of these missions and the incredible scientific information they returned, no one has set foot there for 35 years. Now, at long last, a new generation of explorers is preparing for their own lunar journeys.

The technical challenges of reaching the moon via rockets are well understood. The enormous forces required to propel a spacecraft there, however, are diffi cult to generate; they require rocket engines of incredible size and power. During the Apollo program, the United States relied on the Saturn V rocket, a three-stage system that produced approximately 7.5 million pounds of thrust. The Soviets had hoped to utilize their even-more-powerful N1 rocket, but its 9 million pounds of thrust proved too difficult to manage, and each of the four launch attempts ended in the rocket’s fiery destruction.

Current NASA plans call for a new vehicle, the Orion spacecraft, also known as the Crew Exploration Vehicle (CEV), carried into space by a new rocket, the Ares I. A two-stage system, the Ares I is designed to carry 55,000 pounds to low-Earth orbit, and to transport crews and materials to the International Space Station. The rocket’s first stage is derived from the solid rocket motor currently being used on the space shuttle. The upper stage relies on an updated version of the J-2 engine used during the Apollo program. Although this dependence on it also ensures that the components are well-understood, and that they benefit from lessons learned during decades of development.

For larger payloads, NASA plans to rely on the Ares V, an outsized booster system nearly as large as the Saturn V. The Ares V combines a large external tank, much like that used on the space shuttle, with a pair of five-segment solid rocket motors, also similar to the shuttle’s confi guration. This assembly represents the vehicle’s “core” stage. Above the large fuel tank, two interstage rings separate the core from the Earth Departure Stage (EDS), a spacecraft designed specifi cally for escaping Earth’s gravity. At the top of the Ares V, a composite shroud protects the Lunar Surface Access Module (LSAM) which includes one stage for descending to the moon and another for the crew’s return to lunar orbit.

In its current configuration, the Ares I rocket will carry the CEV into orbit, where the spacecraft will be released to dock with the departure stage and the attached lunar module launched separately aboard the Ares V. Once the Orion spacecraft is firmly docked, the EDS will fire its modified J-2 engine and begin the trip to the moon. Unlike the Apollo missions, the Orion’s crew will leave their spacecraft unmanned while they visit the lunar surface.

Despite the potential of these new rockets, other challenges still face future visitors to the moon. Because it has no atmosphere, there are no weather systems to provide a buffer against extreme changes in temperature. An astronaut standing in sunlight on the moon is quickly heated to 250 degrees Fahrenheit, protected only by the cooling systems contained within her spacesuit. Should that same astronaut move into the shade, the temperature would plummet to minus 250 degrees, forcing the spacesuit’s occupant to rely on in-suit heaters. While this process is maintained automatically, the ability to withstand extreme temperature shifts is critical for systems designed for work on the moon.

At the same time, astronauts working on the moon will have to contend with solar flares and cosmic radiation, streams of high-energy particles that can be harmful to organic tissue and DNA. On Earth, our planet’s magnetic field protects us from these particles, deflecting them, for the most part, back into space. On the moon, however, there is no similar field, and lacking even a faint atmosphere, the particles impact constantly, colliding with the lunar regolith and producing showers of neutron radiation.

The Lunar Reconnaissance Orbiter (LRO) will reach the moon in late 2008, where it will measure space radiation, search for water/ ice, and provide new, highly detailed maps of the lunar surface. This information will provide better understanding of the hazards of the moon and bring lunar cartography into the 21st century; excepting the Apollo landing sites, current moon maps are imprecise, and unusable on the lunar surface. The LRO will use a laser altimeter to create a three-dimensional map of the lunar features, with a margin of error slightly larger than three feet.

Although the design has yet to be finalized, NASA is working on plans for both lunar habitats and rovers hardened against radiation. The presence of water/ice on the moon, suggested by the robotic Clementine mission, might allow for the use of the liquid as a radiation shield. Inflatable habitation modules have been suggested, as have prefabricated systems assembled using robots in advance of the human astronauts. Several new lunar rover designs feature “step-in” spacesuits attached directly to the vehicle body, eliminating  the need for an airlock. These pressurized rovers would allow for a “shirt-sleeve” environment, as well as a greatly increased range of exploration.

According to NASA’s Vision for Space Exploration, the agency plans to have final designs in place by 2012. The fi rst human astronauts should arrive no later than 2020, using the moon to learn more about the solar system, while also developing methods for living on worlds other than Earth. As other nations develop their own strategies for exploring the moon, Earth’s first satellite will eventually become a new outpost for humanity, providing new momentum for a species finally beginning its journey into outer space.

23. Return to the Moon - November 29, 20071.99 MB