A “freeway” through the solar system resembling a vast
array of virtual winding tunnels and conduits around the Sun
and planets, discovered by an engineer at NASA’s Jet
Propulsion Laboratory, Pasadena, Calif., can slash the amount
of fuel needed for future space missions.

Called the Interplanetary Superhighway, the system was
calculated by Martin Lo, who used his theory to design the
flight path for NASA’s Genesis mission, which is currently
using this “freeway in space” on its mission to collect solar
wind particles for return to Earth.

Most missions are designed to take advantage of the way
gravity pulls on a spacecraft when it swings by a body such
as a planet or moon. Lo’s theory mixes in another factor, the
Sun’s pull on the planets or a planet’s pull on its nearby
moons. Forces from many directions nearly cancel each other
out, leaving paths through the gravity fields in which
spacecraft can travel.

Each planet and moon has five locations in space called
Lagrange points, where one body’s gravity balances another’s.
Spacecraft can orbit there while burning very little fuel. To
find the Interplanetary Superhighway, Lo mapped all the
possible flight paths among the Lagrange points, varying the
distance the spacecraft would go and how fast or slow it
would travel. Like threads twisted together to form a rope,
the possible flight paths formed tubes in space. Lo plans to
map out these tubes for the whole solar system.

Lo has turned the theory of the Interplanetary Superhighway
into a tool for mission design called “LTool,” using models
developed at Purdue University, West Lafayette, Ind. The new
LTool designed the flight path for the Genesis mission, the
first space mission to use the theory of the Interplanetary
Superhighway. Genesis launched in August 2001.

The flight path was designed for the spacecraft to leave
Earth and travel to orbit the Lagrange point. After five
loops around this Lagrange point, the spacecraft will fall
out of orbit without any maneuvers and then loop around Earth
to a Lagrange point on the opposite side of the
planet. Finally, it will return to Earth’s upper atmosphere
to drop off its samples of solar wind in the Utah desert, at
the Air Force’s Utah Testing and Training Range.

“Genesis wouldn’t need to use any fuel at all in a perfect
world,” Lo said. “But since we can’t control the many
variables that occur throughout the mission, we have to make
some corrections as Genesis completes its loops around a
Lagrange point of Earth. The savings on the fuel translates
into a better and cheaper mission.”

“It has been exciting and challenging to develop this field.
Our work on the Genesis mission is definitely a high point,”
said Kathleen Howell, co-creator of LTool, and a professor of
aeronautics and astronautics at Purdue. “The theory has been
known for some time, but this is the first time it has been
applied to a space mission.”

“For all missions going to a Lagrange point, LTool will
speed up computations,” Lo said. “Designing the Genesis
spacecraft’s flight path with traditional methods used to
take eight weeks, but now we can design a new flight path in
less than a day — we have redesigned a whole mission in a

Lo envisions a place to construct and service science
platforms around one of the Moon’s Lagrange points. Since the
Lagrange points are landmarks for the Interplanetary
Superhighway, spacecraft could easily be shunted to and from
the station for repair. A team at NASA’s Johnson Space
Center, Houston, working with the NASA Exploration Team
(NEXT), proposes to someday use the Interplanetary
Superhighway for future human space missions.

“Lo’s work has led to breakthroughs in simplifying mission
concepts for human and robotic exploration beyond low-Earth
orbit,” said Doug Cooke, manager of the Advanced Development
office at Johnson. “These simplifications result in fewer
space vehicles needed for a broad range of mission options.”

Lo’s and Howell’s work on the Interplanetary Superhighway for
space mission design was nominated for an annual Discover
Innovation Award by Discover magazine editors and an outside
panel of experts.

Spacecraft are not the only users of the Interplanetary
Superhighway: asteroids and comets are known to travel on it.
Comet Shoemaker-Levy 9 collided with Jupiter when it took an
off-ramp toward the giant gas planet. Scientists think the
asteroid that killed the dinosaurs could have followed
Genesis’ flight path — an iridium deposit at the crash site
shows the asteroid traveled fairly slowly. Just what we might
expect from an asteroid on the Interplanetary Superhighway,
Lo said.

JPL is managed for NASA by the California Institute of
Technology, Pasadena. For more information on Genesis, visit: