NASA's MAP satellite sets sail after lunar flyby
Posted: July 31, 2001

Illustration of MAP's trek past the moon. Photo: NASA
Thanks to a sling-shot past the moon NASA's MAP spacecraft departed Earth orbit this week bound for a quiet spot a million miles away where it will observe the fossil light from the creation of the universe 14 billion years ago.

The Microwave Anisotropy Probe was successfully launched into a highly elliptical orbit around Earth on June 30 by a Boeing Delta 2 rocket.

The spacecraft made three such orbits over the past month. The loops included pre-planned thruster firings during the close approaches to Earth to systematically raise the orbital altitude in advance of Monday's lunar flyby.

MAP made the so-called "phasing loops" to wait for the moon to move into the right position. At about 12:30 p.m. EDT on Monday the spacecraft passed about 3,200 miles above the surface of the moon, receiving a boost from lunar gravity like a sling-shot to propel the 1,850-pound probe toward its final destination -- the second Lagrange Point (L2).

L2 is located a million miles from Earth in the direction opposite the Sun. MAP will become the first satellite to orbit at L2 -- a point where the combined gravity of the Earth and sun will keep the satellite in lockstep with its home planet, always forming a straight line from sun to Earth to MAP.

Controllers expect MAP should reach L2 in about two months.

MAP's $160 million mission is to paint a full-sky picture of the cosmic microwave background radiation left over from the Big Bang, which promises to help scientists answer age-old questions about how the universe formed, its structure, evolution and ultimate fate.

"L2 is a very good place for MAP because it is far from the Sun's and Earth's microwave emissions, which are a billion times stronger than the signal we are measuring," said Elizabeth Citrin, MAP project manager. "And it allows MAP to avoid night/day cycling as the solar arrays always face the Sun and the instrument is always shadowed. The instrument is cooled to about 300 degrees below zero Fahrenheit."

Illustration shows MAP's journey from Earth to L2. Photo: NASA