WASHINGTON — An Orbital Sciences Corp. Pegasus XL rocket making its final manifested flight for NASA delivered the $180 million IRIS solar observatory to orbit June 27.

Short for Interface Region Imaging Spectrograph, IRIS will spend two years studying the region of the sun where the star’s inner and outer regions meet. The observations from the ultraviolet telescope — built by Lockheed Martin Space Systems’ Advanced Technology Center in Palo Alto, Calif., under NASA’s Small Explorer Program — could help improve space weather forecasts, according to NASA.

IRIS’s air-launched Pegasus XL rocket was carried aloft by Orbital’s “Stargazer” L-1011 jet, which took off from Vandenberg Air Force Base, Calif. At 10:27 p.m. EDT, as Stargazer flew 12,000 meters above the Pacific Ocean, it released the Pegasus rocket, which moments later ignited its first-stage solid-fueled motor and sped toward space.

NASA said in a statement posted shortly after launch that Pegasus delivered IRIS to its proper orbit, some 640 kilometers above Earth.

The launch marked the 45th mission for the Pegasus program, which has deployed more than 80 satellites for NASA, the U.S. military and commercial customers.

With the launch of IRIS, Pegasus has flown 28 successful missions in a row for the last 16 years, Ron Grabe, Orbital’s executive vice president and general manager of its Launch Systems Group, said in a statement.

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. He was named senior staff writer in 2004, a position he held...