National Aeronautics and Space Administration officials said the proposals involve exploring the far reaches of the universe, including the Earth's thermosphere and ionosphere, the sun, black holes, the first stars and Earthlike planets around nearby stars.

The space agency is to select two of the proposals next year for full development. NASA said the first mission could launch by 2012 and both will launch by 2015. Mission costs will be capped at $105 million each, excluding the launch vehicle.

"We received many excellent proposals," said Charles Gay, deputy associate administrator for NASA's Science Mission Directorate, "The six we selected for further study offer outstanding science in a small satellite mission."

Each of the selected proposals will be funded by $750,000 to conduct a six-month implementation feasibility study.

The six proposals were submitted by the Naval Research Laboratory, NASA's Goddard Space Flight Center, the Lockheed Martin Space Systems Co., Pennsylvania State University, the University of California-Berkeley and the Massachusetts Institute of Technology.