MAP Trajectory and Orbit

To minimize environmental disturbances and maximize observing efficiency, MAP will observe from a Lissajous orbit about the L2 Sun-Earth Lagrange point 1.5 million km from Earth. The trajectory selected to attain such an orbit consists of 2.5-3.5 lunar phasings loops followed by a ~100 day cruise to L2. No thruster firings are required to enter the L2 orbit.

The Need to go to L2

The Lagrange points mark positions where the combined gravitational pull of two large masses precisely equals the centripetal force required to rotate with them. The L2 Lagrange point offers a virtually ideal location from which to carry out CMB observations. Because of its distance, 1.5 million km from Earth, it affords great protection from the Earth's microwave emission, magnetic fields, and other disturbances. It also provides for a very stable thermal environment and near 100% observing efficiency since the Sun, Earth, and Moon are always behind the instrument's field of view.

MAP Trajectory to L2

The following sketch indicates the path MAP will follow to L2. The trajectory features 2.5 or 3.5 lunar phasing loops which assist the spacecraft in reaching L2. The cruise time to L2 is approximately 100 days after the lunar phasing loops are completed. The launch window for this trajectory is ~20 minutes/day for 7 consecutive days each month. Once in orbit about L2, the satellite maintains a Lissajous orbit such that the MAP-Earth vector remains between 1 and 10 degrees off the Sun-Earth vector to satisfy communications requirements while avoiding eclipses. Station-keeping maneuvers will be required ~4 times per year to maintain this orbit.

MAP Trajectory to L2:

Please help us make this web site more useful and enjoyable by telling us what you would like to see at this site: David N. Spergel / dns@astro.princeton.edu Gary Hinshaw / hinshaw@stars.gsfc.nasa.gov Charles L. Bennett / bennett@stars.gsfc.nasa.gov NASA Privacy Statement NASA IT Security Banner

Last updated: Friday, 05-21-1999