WASHINGTON -- Quirky regions that can serve as parking lots for spacecraft far from Earth are getting increased attention by astronomers and scientists who plot new routes for humans to reach the moon, Mars and asteroids.
These regions -- called Lagrangian orbits or L-points -- are areas where the gravitational forces of two celestial bodies, like the Earth and sun, are in perfect balance. From these spots, not only is the viewing good but spacecraft can remain in position without gobbling up loads of fuel.
In essence, scientists say, L-points are "invisible planets" that occupy large tracts of open space yet allow spacecraft to "land" and stay awhile. Best of all, the view from these L-points is not obstructed by any atmosphere.
L-points were theorized to exist by Joseph-Louis Lagrange, a French mathematician physicist, in 1772. But it wasn't until the Space Age that scientists really could take full advantage of the special properties that exist only at these strange spots in the cosmos.
"You can sit and stare out, keeping the sun and the Earth to your back. That's a perfect situation for doing deep space astronomy."
At the nearest sun-Earth L-point a million miles from Earth, the U.S.-European Solar and Heliospheric Observatory (SOHO) has an uninterrupted view of the sun. Balanced between the pull of Earth's gravity and the sun's gravity, SOHO orbits the sun along with Earth.
The U.S. Advanced Composition Explorer is there too, on the lookout for solar wind and energetic particles that zip by.
First craft at L-point in 1978
As far back as 1978, NASA's International Sun-Earth Explorer 3 was plopped into the L-point, becoming the first spacecraft to orbit a point in space rather than a heavenly body.
Other L-points also are popular. For instance, NASA's Next Generation Space Telescope is headed in 2008 to another of the balance points. At that site, the powerful observatory would always be in Earth's shadow -- great for peering deep into the universe. Even larger telescopes are now being sketched out that also would be placed nearby.
As many as seven other U.S. or European spacecraft, belonging to either Europe or the United States, are
to head for an L-point during the next 10 years.Lagrangian orbits also are likely to serve as jumping off points to reach interplanetary destinations, said Wes Huntress, director of the Geophysical Laboratory at Carnegie Institution of Washington.
"The technology is coming along now where we can move out and claim new territory, to take advantage of and exploit what it offers," he said.
Huntress said that the L-point where the Next Generation Space Telescope is headed is ideal for sets of increasingly more powerful telescopes. While distant from the thermal environment of Earth, space instruments at that L-point are still relatively close, in terms of a communication link.
"You can sit and stare out, keeping the sun and the Earth to your back," Huntress said. "That's a perfect situation for doing deep space astronomy."
Over time, suites of astronomical instruments may well be positioned at L-points, analogous to the cluster of observatories atop Mauna Kea in Hawaii. What would follow then, Huntress said, could be robotic servicing of the spaceborne equipment.
"It may be that our first occupants in the new lands will be robotic. But ultimately as our capability grows to assemble large structures there, I see it as a jumping off point to other places in the solar system. It's the logical place for humans to go and set up shop," he said.
'An ideal staging node'
Human exploration beyond Earth orbit also is on the mind of Robert Farquhar, a space scientist and L-point expert at the John Hopkins University Applied Physics Laboratory, Laurel, Maryland. It was Farquhar, then working at NASA Goddard, who prodded the agency to send the International Sun-Earth Explorer 3 to an L-point in 1978.
"We can establish a human presence at the sun-Earth (L-point). We can build up infrastructure for interplanetary transportation. It's an ideal staging node to go to Mars, Earth asteroids, or even the moon," Farquhar told the American Astronautical Society in Pasadena, California, recently.
Farquhar called for the installation of a mini-space station located near an L-point. One spacecraft would take crew and cargo from low Earth orbit to the vicinity of the L-point. From there, astronauts would board a second spacecraft to the target of their choice.
"One of the first missions would be a human sortie to a near-Earth asteroid," Farquhar said. He outlined the route that should be taken and the asteroid to be visited: 1999 A010. "It would be a one-year round trip, departing (the L-point) on April 7, 2025.
"We need a whole new way to think about human exploration beyond Earth orbit. We've been to the moon ... Let's go somewhere else," Farquhar said.
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