WASHINGTON — A solar observatory and an X-ray astronomy telescope beat out four other finalists competing for $210 million NASA intends to spend over the next several years developing two Small Explorer proposals into ready-to-launch space missions.

NASA announced June 19 that it had selected the sun-watching Interface Region Imaging Spectrograph (IRIS) and the Gravity and Extreme Magnetism Small Explorer (GEMS) concepts to be developed into full missions costing no more than $105 million each, not including a NASA-furnished launch. NASA picked IRIS and GEMS from among a field of six candidate missions selected in May 2008 to receive $750,000 each for six-month mission feasibility studies.

Both selected missions are expected to launch by 2015, although IRIS could launch by the end of 2012, according to Paul Hertz, chief scientist of NASA’s Science Mission Directorate. Although NASA has yet to put the two launches out for bid, both missions are considered strong candidates for the air-launched Pegasus rocket built by Dulles, Va.-based Orbital Sciences Corp., which also will build the spacecraft and perform mission operations for GEMS, according to the lead investigators for the two projects.

IRIS, a 3-meter long spacecraft that will use a solar telescope and spectrograph to unveil the dynamics of the solar chromosphere and transition region, will be built by Palo Alto, Calif.-based Lockheed Martin Advanced Technology Center – home base for IRIS principal investigator Alan Title, a senior fellow there.

Title is an experienced principal investigator who led the development of NASA’s Transition Region and Coronal Explorer, a sun-watching telescope that launched in 1998 and remains in service. He is currently heavily involved in NASA’s Solar Dynamics Observatory mission due to launch in November. He is serving as principal investigator for the Atmospheric Imaging Assembly that will fly aboard the $800 million spacecraft along with two other instruments, including the Helioseismic and Magnetic Imager that was also built in his lab.

Like the Transition Region and Coronal Explorer, IRIS likely will launch aboard a Pegasus in a mission originating from Vandenberg Air Force Base, Calif.

Title said in a June 22 interview that the IRIS instrument will draw heavily upon work done for the Solar Dynamic Observatory. The telescope is a slightly modified version of the Atmospheric Imaging Assembly’s telescope, while the camera, computers and other electronics needed for IRIS will be duplicates of components used on the Solar Dynamic Observatory — either actual leftover hardware or new parts built from finished designs.

Despite having some hardware in common with the much larger and more expensive Solar Dynamic Observatory, IRIS is a very different spacecraft with a very different mission.

“It’s got a telescope that has a very similar configuration, however it works in a very different wavelength range and it carries a spectrometer,” Title said.

He said IRIS will complement the Solar Dynamic Observatory and the nearly three-year-old U.S.-Japanese Hinode mission, much as Transition Region and Coronal Explorer complemented the Solar and Heliospheric Observatory that has been watching the sun since 1995.

Title said the atmospheric imager aboard the Solar Dynamic Observatory will do “a wonderful job of following events that propagate through the corona” but will not be able to see events as they start lower down in the sun’s chromosphere.

“IRIS makes images in the chromosphere and transition region and also gets high-resolution spectra in that region,” Title said.

Both the instrument and spacecraft will be built by Lockheed Martin. Major partners on the project include NASA Ames Research Center at nearby Moffett Field, Calif., the Smithsonian Astrophysical Observatory in Cambridge, Mass., and Montana State University in Bozeman.

Title said the mission would not be possible if not for theoretical work being done at the Institute of Theoretical Astrophysics in Oslo, Norway.

“Essentially the driver for the IRIS mission is the development of new numerical simulations that allow us to model the chromospere and transition region,” Title said. “We’ve known for decades now that the heating of the corona starts in the chromosphere. We haven’t built instruments to look at this region not because they were difficult to build but because no one knew how to interpret the data.”

GEMS, the second of the newly selected Small Explorer missions, is being lead by Jean Swank, a veteran astrophysicist at NASA’s Goddard Space Flight Center, Greenbelt, Md.

The heart of the 267-kilogram GEMS spacecraft is a specialized X-ray telescope that will study neutron stars, black holes and other exotic objects. The telescope is specially constructed to measure the polarization of X-rays emitted from matter trapped near black holes.

According to Swank, only one cosmic object — the Crab Nebula — has been measured in X-rays that have become polarized, or forced to vibrate in only one direction, as when light scatters off of a surface. During its nine-month primary mission, GEMS has the potential to make breakthrough discoveries about black holes and neutron stars by detecting and measuring the polarization of X-rays emitted by some of the most energetic objects in the universe.

“After we make these 9 months of observations we hope that there will be a Guest Observer program for the community, as the spacecraft and systems will be sized to operate at least 2 [years],” Swank told Space News in an e-mail.

A Guest Observer program would allow researchers beyond the core science team to use GEMS for observations.
The GEMS instrument will be built at Goddard, with Orbital Sciences responsible for the spacecraft and mission operations. ATK Space of Goleta, Calif., will build a boom to place the X-ray telescope the proper distance from the detectors.

Major partners include Ames and the University of Iowa. Science operations will be based at Goddard.

IRIS and GEMS stand to be NASA’s 12th and 13th Small Explorer missions selected for flight. NASA’s previous calls for proposals, issued in 2003, yielded two missions, the Interstellar Boundary Explorer spacecraft launched in October 2008 and the Nuclear Spectroscopic Telescope Array, which Hertz said will launch in 2011.

NASA stopped work on the latter mission, led by the California Institute of Technology in Pasadena, Calif., in 2006 but reversed course late the following year.

Hertz said NASA’s Explorer Program budget profile should permit the agency to release a new call for proposals once every two years.

NASA’s next such announcement of opportunity will be for a Medium Explorer, a mission class last called for in 2001. That solicitation produced the Time History of Events and Macroscale Interactions during Substorms small spacecraft constellation that launched in October 2006 aboard a Delta 2 rocket. The other mission selected that year, the Wide-field Infrared Explorer, is due to launch later this year.

Hertz said NASA intends to solicit its next round of Medium Explorer proposals “as soon as NASA has an appropriate launch vehicle under contract and certified.”

The Delta 2 rocket NASA traditionally relied on to launch Medium Explorer and many other midsized satellites is being phased out as the U.S. Air Force – an important anchor tenant for that vehicle – prepares to rely almost exclusively on the larger Delta 4 and Atlas 5 rockets, which were developed under the Evolved Expendable Launch Vehicle program.

Firms vying to offer Delta 2-class launch services to NASA included Orbital and Hawthorne, Calif.-based Space Exploration Technologies (SpaceX), both of which are developing new rockets with financial assistance from NASA’s Commercial Orbital Transportation Services demonstration program.

first Falcon 9 rocket has been delivered to Cape Canaveral Air Force Station, Fla., in preparation for a maiden launch the company hopes to conduct this year. Orbital’s Taurus 2 is not expected to make its debut before 2010.

Hertz could not say when, exactly, NASA expects to be able to issue a new Medium Explorer solicitation.

“There is reason to be optimistic that it won’t be too long before we can move forward with a solicitation for [Medium Explorer] missions comparable to those we used to launch on the Delta 2,” Hertz said.

Brian Berger is editor in chief of SpaceNews.com and the SpaceNews magazine. He joined SpaceNews.com in 1998, spending his first decade with the publication covering NASA. His reporting on the 2003 Space Shuttle Columbia accident was...