An illustration of the Imaging X-ray Polarimetry Explorer (IXPE) spacecraft. Credit: NASA

GRAPEVINE, Texas — NASA has selected an X-ray astronomy spacecraft to study black holes and other astronomical phenomena as the next flight in a program of small astrophysics missions, the agency announced Jan. 3.

The Imaging X-ray Polarimetry Explorer (IXPE) spacecraft, scheduled for launch in late 2020, will be a small spacecraft with three telescopes designed to measure the polarization of X-rays. Measuring how the X-rays are polarized can provide insights into the high-temperature environments where they are created.

“We cannot directly image what’s going on near objects like black holes and neutron stars, but studying the polarization of X-rays emitted from their surrounding environments reveals the physics of these enigmatic objects,” Paul Hertz, director of NASA’s astrophysics division, said in a statement. “XPE will open a new window on the universe for astronomers to peer through.”

IXPE was one of three finalists selected by NASA in July 2015 in the latest round of the Small Explorers program, intended for small space science missions with a cost cap, excluding launch, of $125 million. The other two finalists were an all-sky infrared survey spacecraft called SPHEREx and another X-ray polarimetry mission, the Polarimeter for Relativistic Astrophysical X-ray Sources, or PRAXyS.

The total cost of IXPE, including launch and operations, will be $188 million, according to the NASA announcement. The release did not indicate what vehicle would launch IXPE, but previous presentations about the proposed mission stated it was designed to launch on an Orbital ATK Pegasus XL, a vehicle that has been used by NASA for other small space science missions.

The principal investigator for IXPE is Martin Weisskopf, chief scientist for X-ray astronomy at NASA’s Marshall Space Flight Center and project scientist for the Chandra X-Ray Observatory spacecraft. IXPE will be built by Ball Aerospace, with the Italian space agency ASI providing polarization sensitive X-ray detectors for the spacecraft.

The overall Explorers program, which includes both small and medium classes of missions, is intended to provide more frequent access to space for astronomers than larger missions. Those programs include both standalone spacecraft missions as well as “missions of opportunity” for flying instruments on balloons or other spacecraft, including the International Space Station. NASA expects to select a mission of opportunity for the Small Explorers program from two finalists, a balloon-borne observatory of high-frequency radio emissions and a contribution to a Japanese cosmic microwave background mission, in the spring.

NASA, in an update of its Astrophysics Implementation Plan report issued in December, said it would carry out four Explorer program solicitations in the decade of 2012 through 2021. That was a recommendation made in a report issued last year assessing NASA’s progress in carrying out the 2010 decadal survey.

NASA issued an announcement of opportunity for a Medium Explorer mission in September, with a cost cap of $250 million excluding launch. NASA plans to select a set of finalists in mid-2017 for further study, choosing one mission in early 2019 for launch by the end of 2023. NASA also plans another round of Small and Medium Explorer competitions in 2019 and 2021, respectively.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...