Two new Small Explorer missions selected by NASA
NASA NEWS RELEASE
Posted: July 11, 2002

Spacecraft that will observe the Earth's highest clouds and detect hidden matter in the universe have been chosen as the next two missions in NASA's Small Explorer (SMEX) program.

"From the time Explorer 1 was launched more than 40 years ago and discovered the Van Allen radiation belts, Explorer satellites have made impressive discoveries by obtaining significant science at the lowest cost," said Edward Weiler, Associate Administrator for Space Science, NASA Headquarters, Washington. "The two missions we've selected will continue in the Explorer tradition by investigating some of the most fundamental questions raised in space science."

The first mission, to be launched in 2005, is the Explorer for Spectroscopy and Photometry of the Intergalactic Medium's Diffuse Radiation (SPIDR), a mission to map the "cosmic web" of hot gas that spans the universe. Half of the normal matter in the nearby universe is in filaments of hot gas, and SPIDR will observe its emission and distribution for the first time.

SPIDR's data will answer fundamental questions concerning the formation and evolution of galaxies, clusters of galaxies, and other large structures in the universe as well as address a number of questions related to hot gas in our own galaxy. An innovative and sensitive spectrograph design will be placed into a high earth orbit to observe emission lines from important atomic tracers of mass in the intergalactic medium. Supriya Chakrabarti of Boston University will lead SPIDR at a total cost to NASA of $89 million.

The second mission, to be launched in 2006, is the Aeronomy of Ice in the Mesosphere (AIM) Explorer, which will determine the causes of the highest altitude clouds in the Earth's atmosphere. There are indications that the number of clouds in the upper atmosphere (mesosphere) over the Earth's poles has been increasing over the past couple decades, and it is hypothesized that this results from increasing concentrations of greenhouse gases at high altitudes.

AIM will measure atmospheric temperatures and water vapor concentrations in the cloud forming region, as well as the properties of the clouds themselves. This will help determine the connection between the clouds and their environment and serve as a baseline for the study of long-term changes in the upper atmosphere. James Russell III of Hampton University in Hampton, Va., will lead AIM at a total mission cost to NASA of $92 million.

The Explorer Program is designed to provide frequent, low- cost access to space for physics and astronomy missions with small to mid-sized spacecraft. Six SMEX missions have been launched since 1992, and five of them are still operating and returning science data. The Galaxy Evolution Explorer (GALEX) will be the seventh SMEX mission and is scheduled for launch in September 2002. GALEX will study the history of star formation in the universe by measuring the ultraviolet light from newly formed stars in galaxies out to a distance of 10 billion light years.

The selected proposals were among 33 SMEX and 13 mission-of- opportunity proposals originally submitted to NASA in February 2000 in response to an Explorer Program Announcement of Opportunity issued in November 1999. NASA selected seven proposals in September 2000 for detailed feasibility studies. Funded by NASA at $450,000 each, these studies focused on cost, management and technical plans, including small business involvement and educational outreach. NASA's Goddard Space Flight Center, Greenbelt, Md., manages the Explorer Program for the Office of Space Science, Washington.

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