Spacecraft to travel ‘interplanetary superhighway’

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    Two small aerospace companies are developing a 100-kilogram spacecraft to fly to a point where the gravitational pulls of the Earth and Moon balance each other. If NASA approves the second phase of the project, the craft will be launched in 2008 to test an inexpensive, low-energy route to space called the "interplanetary superhighway".

    SpaceDev of Poway, California, US, and Andrews Space of Seattle, Washington, US, are developing the tiny spacecraft, called SmallTug. Like the European Space Agency's SMART-1 probe - now in lunar orbit - it would rely on solar-powered electric propulsion, which generates a small, continuous thrust. This highly efficient approach cuts costs dramatically, but takes about a year to reach the Moon on a circuitous, spiral path.

    But rather than orbit the Moon, SmallTug will target a point in space called lunar Lagrange-1 (L1). Lagrange points are places where the opposing gravitational pulls of two bodies are in perfect balance. There are five such points around any two bodies, and objects placed at these points "stay put" with respect to the bodies.

    To take advantage of this stability, several satellites have been placed at the L1 point of the Earth-Sun system, and one, the Wilkinson Microwave Anisotropy Probe, is now at the Earth-Sun L2 point. But SmallTug will be the first spacecraft placed at the Earth-Moon L1 point, which is about 85% of the distance towards the Moon from the Earth. It will fly around the point in a loop to maintain its stability.

    Tube network
    This point was chosen because it is a gateway to a network of low-energy trajectories to faraway destinations. These trajectories are the product of chaos theory and allow small forces to propel spacecraft a long way. Topologically, the paths look like a network of tubes - routed through balancing points such as lunar L1 - that connect various objects in the solar system.

    This interplanetary superhighway is what most spacecraft use when they fly by planets to gain speed or change direction in "gravity assists", explains Martin Lo, a mathematician at NASA's Jet Propulsion Laboratory in Pasadena, California, US. He designed SmallTug's trajectory and used the same approach to map out NASA's Genesis mission, which circled the Earth-Sun L1 point to collect solar wind samples before returning in 2004.

    The lunar L1 point could serve as a jumping-off point for trips to Mars as well as the Moon, says Jim Benson, chairman and CEO of SpaceDev. Lo adds it could also make a convenient service station for future missions parked at the Earth-Sun L2 point, such as the James Webb Space Telescope, planned for launch in 2011.

    Future spacecraft could also be sent to the lunar L2 point, on the far side of the Moon. A spacecraft could circle that point in a large halo-like orbit that would be visible from Earth. It could serve as a relay satellite for future optical or radio telescopes that might be built on the far side of the Moon.

    SmallTug is light enough to be launched as a hitchhiker on another satellite, and the whole project should cost less than $20 million, Benson told New Scientist. SMART-1 cost £77 million ($135 million).


    http://www.newscientistspace.com/ar...ft-to-travel-interplanetary-superhighway.html
     

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