The National Aeronautics and Space Administration said both proposals involve projects that will study the sun and some of the most exotic objects in the universe. Both missions will be launched by 2015; the first by the end of 2012. Mission costs will be capped at $105 million each, excluding the launch vehicle.
One project, from the Lockheed Martin Corp., is the Interface Region Imaging Spectrograph mission. NASA said it will use a solar telescope and spectrograph to explore the solar chromosphere -- the gaseous layer of the sun's atmosphere that's visible during a total solar eclipse -- a crucial region for understanding energy transport into the solar wind. Recent discoveries have shown the chromosphere is significantly more dynamic and structured than previously thought.
The other project, developed by NASA's Goddard Space Flight Center, will detect and measure the polarization of X-rays emitted by objects such as neutron stars and stellar-mass black holes.
The Small Explorer program is designed to provide frequent, low-cost access to space for heliophysics and astrophysics missions using small- to mid-sized spacecraft.