Tuesday, May 13, 2008

Returning to the Moon

Continued from page 1

By Brittany Sauser

The human body responds to radiation in different ways, depending on the intensity, duration, and composition of the radioactive particles. The two things that scientists are most worried about are acute radiation poisoning from, for example, a solar flare, and long-term exposure to galactic cosmic rays, which can increase the risk of cancer. "In all cases, the danger is that ionizing radiation [high-energy, charged particles] can break the atomic bonds in DNA and damage cells and tissue," says Kasper.

The radiation detector consists of a series of silicon semiconductors, each about 35 millimeters in diameter and one millimeter tall. In between the pieces of silicon, the scientists have inserted large blocks of material called tissue-equivalent plastic. "The blocks are waxy and look like giant black crayons but have the same chemical composition as human tissue," says Kasper.

So while the silicon gauges the energy and composition of particles as they come flying through the detector (a proven technique for measuring radiation), the plastic is used to measure their biological effects. Previously, data from radiation detectors was sent back to Earth, where scientists attempted to calculate the effect that the measured radiation would have on humans. The plastic material provides a direct and more-accurate measurement of what radiation is like at different depths of human tissue, says Kasper.

The second instrument making its first spaceflight is the lunar orbiter laser altimeter (LOLA), developed by engineers at NASA Goddard Space Flight Center. It uses laser light to measure the distance between the spacecraft and the surface of the Moon. "It is going to measure that distance very precisely, to about 10 centimeters, and it will make measurements 28 times per second," says NASA's Smith, who is also the principal investigator for LOLA. Unlike current instruments, which send out a single laser beam at low repetitions, the new altimeter sends out five focused beams of laser light that are reflected back and received by five separate detectors, for a total of 140 measurements per second.

This allows scientists to make a high-density, very precise map of the shape of the lunar surface. "We can determine the altitude and slope of different spots on the Moon as well as the roughness of the terrain," says Smith. "We can also learn about the properties of the surface--for example, the shape of craters and their depth and size." The end goal is to identify the best spot, preferably flat, for a large lander to touch down and for astronauts to make a base.

Crater and LOLA will be accompanied on the lunar orbiter by four other instruments that will be imaging and mapping the Moon, measuring surface temperatures to identify potential ice deposits, and searching for hydrogen in the lunar polar regions. All the data will be continuously sent back to Earth for analysis.

"LRO is the first of our exploration missions for a return to the Moon and will have a significant impact on future human spaceflight," says Vondrak.