100 years on
Magazine Within a Magazine. Celebrating 200 Years of Flight
- By the Editors
- Air & Space magazine, January 2004
Our imagined magazine, the issue that we think could appear in December 2103, referred to a space elevator and an interferometer stationed at a Lagrange point. Here are some of the preparations being made for technologies that will appear in another hundred years.
The L2 Lagrange Point
Eighteenth-century Italian-French mathematician Joseph-Louis Lagrange was the first to identify points in space where the gravitational tugs of two bodies are in balance. Any two bodies in mutual orbit, whether the Earth and Moon or the Earth and Sun, have five such locations (also called libration points) where a spacecraft won't be pulled into either body's orbit.
Since the 1960s, space mission designers have known about halo orbits -- small, tight circles around Lagrange points that allow a spacecraft to remain "parked" in interplanetary space with minimal fuel usage.
The Earth-Sun L2 point, located roughly one million miles from Earth in a direction away from the Sun, is the preferred destination for several planned NASA and European space telescopes. The Wilkinson Microwave Anisotropy Probe is already there, and more spacecraft will be stationed there in the next decade or two, including the James Webb Space Telescope and NASA's proposed Terrestrial Planet Finder. Many of these will be infrared telescopes, which work more effectively the farther they are from the warm, glowing Earth.
NASA also has been looking at L2 and other libration points as convenient staging points for human missions to the moon, Mars, and asteroids.
Astronomers have long known that combining the light from many telescopes effectively creates a single, giant telescope. This has been done on the ground with radio dishes like the Very Large Array in New Mexico. Eventually, astronomers want to build optical interferometers, made of many orbiting mirrors, that can "see" in ordinary visible light. A big step in developing the technology for these kinds of instruments will be NASA's Space Interferometry Mission scheduled for launch in 2009.
The Terrestrial Planet Finder, whose job will be to search for Earthlike planets, may be built as an interferometer, but it is undecided whether the elements will be attached to a common "boom" or will fly in formation, with their positions kept extremely stable.
Future space telescopes will have lighter mirrors that replace the heavy, old-fashioned glass in use today. Astronomers are now exploring these future telescope arrays at a conceptual level.