Machine Design

Back to the Moon

NASA starts down the road for returning astronauts to the Moon.

Senior Editor

LRO is the first step in a planned 2018 return of humans to the Moon which, in turn, should lead to a lunar base.

The Lunar Reconnaissance Orbiter is scheduled for lift-off in Fall of 2008. It will spend a year circling 30 miles above the Moon as it maps the topology, temperature distribution, and radiation, and searches for water in preparation for NASA putting humans back on the Moon.

The upper stage of the rocket that sent LRO into space and onto the Moon (right) will serve as a 2,000-kg impactor, hopefully kicking up a plume of ice-rich dust when the Shepherding Spacecraft (above) sends it crashing into one of the deeper craters on the lunar surface. Shortly thereafter, the Shepherding craft will fly itself into the Moon, sending up a second plume.

After almost three-and-a-half decades since man last walked on the Moon, NASA is making ambitious plans and sketching hardware designs for a return trip and eventual long-term, manned lunar outposts. The first big step takes place Oct.1, 2008 when NASA launches its Lunar Reconnaissance Orbiter (LRO). Its mission is to map the Moon's surface with exacting detail, includingthe radiation on the surface and in orbit around it, the suitability of potential landing sites for future manned and unmanned missions, and, with luck, discover resources useful to future explorers, such as water.

The spacecraft will weigh about 2,400 lb when it lifts off atop an Atlas V or Delta IV rocket from Kennedy Center. About 1,000 lb of the LRO will be propellant for its thrusters. After a fourday transit, the probe will inject itself into a 62-mile-high polar orbit around the Moon, an altitude that will slowly drop to about 31 miles. Solar arrays and lithiumion batteries will generate about 400 W, though it should only take 100 W to power its scientific payload and communication suite.

The craft will receive instructions from Earth and make lowrate downlinks via S-band, relying on a Ka-band radio for highrate downlinks (100 to 200 Mbps or 900 Gbytes/day).

The major part of the mission would last a year. After that, a five-year extension could be added. The extended mission would place the satellite in a higher, low-maintenance orbit. The LRO costs about $400 million, and launching and maintaining it through the first year will add another $90 million.

LRO will carry eight instruments to map the Moon:

CRaTER (Cosmic Ray Telescope for the Effects of Radiation). On the surface of the Moon, cosmic rays and solar flares can damage human DNA and raise the risk of cancer and other diseases. And millions of years of being bombarded with radiation has left the lunar surface radioactive enough to possibly injure astronauts.

CRaTER will determine radiation levels on the Moon's surface using a stacked-detector design. The detectors have been space proven on previous missions, including the Polar Imaging Proton Spectrometer that has been circling Earth and measuring radiation since 1996. Portions of CRaTER's radiation detectors will be blocked by varying thicknesses of special plastic engineered to have the a density and composition similar to human tissue. This will let scientists see how highly energetic particles might penetrate and interact with the human body.

Diviner. Apollo missions all took place in the lunar equatorial region and during the lunar day. But NASA plans two-week stays on the Moon during which they will explore a wider range of latitudes. Diviner, a nine-channel solar reflectance and infrared filter radiometer, will give scientists a clearer picture of temperatures over the entire surface of the Moon. It will use two telescopes that collect images on uncooled thermopile detectors. An articulated mount lets the telescopes move and view the lunar surface, space near it, and calibration targets mounted on the side of the Orbiter. Besides mapping the Moon's thermal signature, Diviner should also help detect near-surface and exposed ice, as well as determine if potential landing sites are too rocky.

LAMP (Lyman-Alpha Mapping Project). The Moon barely has an atmosphere, so sunlight does not get scattered as it does on Earth. This means shadows are inky black. And the Moon's orbit and rotation create permanently shadowed regions that never see the light of day. LAMP will let researchers "see" what is in these dark shadows. It will scour a narrow band of UV wavelengths looking for starlight reflected by whatever is in the shadows. This wavelength coincides with the glow given off by hydrogen gas that permeates the universe and should also be "lighting'" up the lunar landscape.

If LAMP succeeds, NASA will map the Moon's darkened regions, demonstrate the use of such technology for future manned and robotic missions, and collect data on the composition and variability of the thin lunar atmosphere. There's also a chance it might uncover ice, which gives off a characteristic spectral emission in the same wavelength as hydrogen.

LEND (Lunar Exploration Neutron Detector). Cosmic rays smacking into the Moon penetrate up to 6 ft into the surface before being reflected back, creating a neutron-fueled glow or albedo. LEND will analyze that glow. If the glow dips in an area, it could mean the neutrons are being absorbed by a hydrogen-bearing compound in the vicinity, such as water.

NASA engineers estimate LEND can detect hydrogen in fractions as small as 100 ppm, which will make it invaluable in detecting surface and near-surface ice. LEND's passive collimators collect neutrons while nine sensors quantify the returns. The device, designed by an engineer at the Space Research Institute in Moscow, will also spend time analyzing and mapping thermal energies (up to 15 MeV) in the lunar atmosphere.

LOLA (Lunar Orbiter laser Altimeter). To make landings and travel on the Moon safer, LOLA will closely map the topology of the lunar surface. This will also serve as a baseline, so future researchers will be able to remap the surface and note any changes.

The altimeter sends a single laser through a diffractive optical element that splits the laser into five beams, each of which gets sent to the surface. The spots form a cross about 150-ft wide on the surface. For each beam, LOLA measures the time of flight (range) to within 0.6 nsec (4 in.), pulse spread (surface roughness), and compares transmitted to reflected energy (reflectance). The five beams also create a 2D spot pattern, which will let the device unambiguously determine slopes along and across the spacecraft's orbital path. By sending a laser signal down to the Moon 28 times/sec, the device will make 4 billion measurements by the end of the year, creating a more precise 3D map of the lunar surface than we have of the Earth.

LOLA will also look for ice by measuring the brightness of laser reflections. A change as small as 4% could mean ice.

The change in brightness, however, might also be from some kind of reflective crystals. But if bright spots coincide with dark shadows, NASA would strongly suspect the presence of ice in those locations.

LROC (Lunar Reconnaissance Orbiter Camera). The probe carries LROC, a high-resolution camera that will photograph the surface of the Moon, including the poles. It will give scientists a way to identify potential landing sites near the poles (where the ice may be). LROC will use two narrow-angle camera heads. Its resolution will transform a half-meter square into a single pixel. This is thought to be enough for good topological detail. For example, it should let scientists pick out equipment, spacecraft, and rovers left on the Moon by Apollo missions.

LCROSS (Lunar Crater Observation and Sensing Satellite). In 1998, NASA crashed the Lunar Prospector probe into the Moon, hoping to spot signs of water in the plume of dust and rocks it kicked up when it hit. But they detected no evidence of water through their telescopes. They might have had their instruments pointed in the wrong place, smashed the spacecraft into a "dry" area, or perhaps there just isn't any water on the Moon.

NASA is going to try again with LRO's LCROSS, sort of a Prospector on steroids. The LCROSS mission sends a 200-kg "kinetic impactor" (actually, the used up Earth Departure Upper Stage) into the bottom of a crater at the lunar south pole. It should hit with 200 times the energy of the Prospector and throw up a 1,000-ton plume 40-miles high.

The cloud of debris should be visible to Earth-based stations and satellites in orbit around the Moon. The mission includes the Shepherding Spacecraft, which gets ferried to lunar orbit by the LRO. It will guide the impactor into the Moon, then fly through the plume for a close-up examination of dust, debris, and, hopefully, signs of water. The 700-kg Shepherd then becomes a second impactor and crashes into the Moon, giving observers a second chance to search for signs of water.

As you can see from the list of LRO instruments and goals, water is the Holy Grail. Finding ice, for example, would let astronauts mine and refine water, which is necessary for survival.

Astronauts could also extract hydrogen and oxygen from water, two useful resources for a colony or outpost.

Why we're bound for the Moon

The main reason NASA is planning a return to the Moon is to use it as a proving ground for technologies that will be employed on a manned mission to Mars.

"Just three days away, the Moon is a nearby place where astronauts can learn to live and work in a hostile environment before heading off to more distant destinations," says NASA.

NASA point to several key areas in which it could get valuable insights by setting a full-fledged manned habitat on the Moon. Such an outpost would let NASA test next-generation space suits and robotic rovers. It would let them try new methods of protecting astronauts from radiation. They would also learn how to best operate and service a variety of life-support systems, as well as various power supplies, including solar panels and nuclear plants. And from a biomedical standpoint, a manned base would let them gauge the effect of reduced gravity on the human body.

NASA also points to "scientific and economic" reasons for a trip back to the Moon. Scientists based there could learn more about the origins of the Earth and solar system. It would also be a good spot to place an observatory and track meteors and asteroids that might hit the Earth. And it could be built into a spaceport to support space launches to Mars.

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.