ScienceMaster - Aerospace Engineer Aprille Ericsson

MAP is part of the Explorers Program, selected by NASA in 1996, to probe conditions in the early universe. MAP measures temperature differences ("anisotropy") in the cosmic microwave background radiation.

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.

To answer these questions MAP must measure the temperature fluctuations of the cosmic microwave background radiation over the entire sky.

The cosmic microwave background radiation is the radiant heat left over from the Big Bang. It was first observed in 1965 by Arno Penzias and Robert Wilson at the Bell Telephone Laboratories in Murray Hill, New Jersey. The properties of the radiation contain a wealth of information about physical conditions in the early universe and a great deal of effort has gone into measuring those properties since its discovery. The radiation (and by extension, the early universe) is remarkably featureless; it has virtually the same temperature in all directions in the sky.

MAPS Predecessor; the Cosmic Background Explorer

In 1992, NASA's Cosmic Background Explorer (COBE) satellite detected tiny fluctuations, or anisotropy, in the cosmic microwave background. It found, for example, one part of the sky has a temperature of 2.7281 Kelvin (degrees above absolute zero), while another part of the sky has a temperature of 2.7280 Kelvin. These fluctuations are related to fluctuations in the density of matter in the early universe and thus carry information about the initial conditions for the formation of cosmic structures such as galaxies, clusters, and voids. COBE had an angular resolution of 7 degrees across the sky, 14 times larger than the Moon's apparent size. This made COBE sensitive only to fluctuations of large extent. MAP will measure anisotropy with much higher resolution than COBE did and the new information contained in these smaller size fluctuations will shed light on several key questions in cosmology.