Updated 9:00 p.m. Eastern

WASHINGTON — A Northrop Grumman Antares rocket successfully launched a Cygnus spacecraft April 17 carrying nearly three and a half metric tons of cargo bound for the International Space Station.

The Antares lifted off from the Mid-Atlantic Regional Spaceport at 4:46 p.m. Eastern after a countdown marred by only a brief issue with the rocket’s transporter/erector that was resolved earlier in the afternoon. The Cygnus separated from the Antares rocket’s upper stage nine minutes after liftoff in what controllers said was a nominal orbit, and deployed its solar panels nearly three hours later.

“The spacecraft is very healthy. It’s performing very well,” Frank DeMauro, vice president and general manager of space systems at Northrop Grumman said at a post-launch briefing. The spacecraft had, after liftoff, performed two maneuvers called “targeted altitude burns” to raise its orbit. Those burns are a new capability on the Cygnus, he said, that helps shorten the time it takes for the spacecraft to reach the station.

The Cygnus, carrying 3,436 kilograms cargo, is scheduled to be captured by the station’s robotic arm at about 5:30 a.m. Eastern April 19. It will remain at the station for about 90 days before being unberthed, after which it will move to a higher orbit and fly an extended mission of at least six months to test its ability to serve as a free-flying platform for experiments and technology demonstrations.

Of that cargo, 1,569 kilograms is set aside for science investigations. That research includes a rodent experiment to test the effects of spaceflight on the function of antibody production and immune memory, an experiment by a company called FOMS to test the production of high-quality optical fibers in microgravity and two robots called Astrobees that will be able to maneuver within the station supporting research there.

The Astrobees are a successor to SPHERES, a set of small, spherical robots that have been on the station for several years for technology demonstration and educational applications. “SPHERES has been on orbit for more than a decade,” said Maria Bualat of NASA’s Ames Research Center at a pre-launch briefing April 16. “They’re kind of limited in their compute power, and they’re just aging.”

Besides the Cygnus, the Antares carried 60 “ThinSat” secondary payloads, released from the rocket’s upper stage several minutes after the Cygnus deployment along with a single conventional cubesat. Each ThinSat is has the same length and width of a single-unit cubesat but is only a fraction as thick, enabling more to be flown in the same volume.

Students from schools in nine states built the ThinSats flown on this mission as part of educational projects sponsored by the Virginia Commercial Space Flight Authority. The ThinSats, deployed in orbits at an altitude of 200 to 250 kilometers, will remain in orbit for about five days before they reenter. “It’s going to give us a lot of information that normally doesn’t get picked up” because satellites rarely operate at such low altitudes, said Chris Hale, program manager for Virginia Space ThinSat Program.

The five-day lifetime has another advantage, added Bob Twiggs, the co-investor of the cubesat who helped design the ThinSat concept and its educational curriculum: “It’s the attention span of the students.”

This mission, designated NG-11, is the last for the company under its original Commercial Resupply Services (CRS) contract awarded by NASA in 2008. Subsequent missions, starting with NG-12 this fall, will be performed under the CRS-2 contract awarded in 2016.

Those missions will make use of an upgraded version of the rocket called the Antares 230+ with several changes to improve its payload performance by up to 800 kilograms, said Kurt Eberly, Antares vice president at Northrop Grumman. Those improvements including reducing the vehicle’s mass and strengthening its structure to allow its RD-181 engines to remain at 100 percent thrust throughout ascent.