WASHINGTON — The next Northrop Grumman Cygnus cargo mission to the International Space Station will demonstrate two new capabilities, one before launch and the other after the spacecraft departs the station.

The Cygnus spacecraft, flying a mission designated NG-11, is scheduled to launch at 4:46 p.m. Eastern April 17 on an Antares rocket from the Mid-Atlantic Regional Spaceport at Wallops Island, Virginia. During a pre-launch press conference April 16, officials reported no problems with launch preparations and excellent weather, with a 95 percent chance of acceptable conditions at the scheduled liftoff time.

The Cygnus is carrying more than 3,400 kilograms of cargo on this mission to the station. Of that total, 1,569 kilograms is for a variety of scientific investigations, with 936 kilograms of crew supplies. The remainder is split among vehicle hardware, miscellaneous equipment and a satellite deployer for NanoRacks.

For the first time, some of that cargo will be loaded onto the Cygnus just 24 hours before launch. The NG-11 mission is the first to demonstrate a “late load” capability of cargo after the vehicle has been rolled out to the launch pad. Six cargo bags will be loaded onto the Cygnus at that time, said Andrew Zarechnak, Cygnus vehicle manager at Northrop Grumman, at a pre-launch science briefing.

“It allows us to do more science on this vehicle and allows more types of science to get to the station,” he said. That includes a rodent research experiment that features 40 mice, the first time such an experiment has flown on the Cygnus. Similar experiments in the past had to fly on SpaceX’s Dragon, which already has the ability to load cargo into the vehicle within a day of launch.

That late load makes use of a new “pop-top” payload fairing for the Antares, whose top can be removed to allow access to the Cygnus. A mobile payload processing facility is moved into place around the fairing while the rocket is horizontal at the pad so that crews can access the Cygnus to load that cargo.

The Cygnus is scheduled to be berthed to the ISS by the station’s robotic arm April 19 and remain at the station for about 90 days. After being unberthed, it will maneuver into a higher orbit to deploy satellites.

On past missions the Cygnus has deorbited within a few weeks of departing the station, but on the NG-11 mission Northrop Grumman plans to keep Cygnus in orbit for months to test its ability to serve as a free-flying research platform.

“We’re going to start an extended duration mission for Cygnus where we’re going to demonstrate the ability of Cygnus to fly long periods of time in space, where it can be an excellent testbed for scientific experiments,” said Frank DeMauro, vice president and general manager of space systems at Northrop Grumman.

To enable that extended mission, the Cygnus now has a control moment gyro to handle the attitude control of the spacecraft, reducing the need for it to use thrusters. That saves fuel that can instead be used to maintain its orbit and perform other maneuvers, extending the spacecraft’s lifetime in orbit.

DeMauro said the company hopes to demonstrate that the Cygnus, as a free-flying spacecraft, can be a platform for scientific research and technology demonstrations. “We want to demonstrate the really pristine microgravity environment that Cygnus will provide,” he said. That could include, on future missions, flying away from the ISS to perform experiments for a time before returning so that the experiments can be retrieved.

The company hasn’t set a firm timetable for that extended mission. DeMauro said the company would like to keep the NG-11 Cygnus in orbit at least until after the launch of the NG-12 Cygnus some time in the fall. That would allow Northrop Grumman to demonstrate the ability to operate two Cygnus spacecraft simultaneously from the same control center.

“We’re thinking something on the order of six to seven months as a minimum mission duration,” he said. “Once we achieve that goal, if we’ve achieved all the other goals, then we’ll regroup and determine how much longer we might want to fly the vehicle.”

The NG-11 Cygnus mission is the first of two commercial cargo spacecraft set to fly to the ISS this month. SpaceX is scheduled to launch its latest Dragon cargo spacecraft to the station April 26 from Florida. That back-to-back scheduling, said Joel Montalbano, deputy manager of the ISS program at NASA, was a result of when the missions were ready to fly.

“Do we plan missions a week apart? Generally we don’t do that,” he said. “Our plan is to fly when the customers are ready.”

This mission is also the last one from the original Commercial Resupply Services (CRS) contract awarded to what was then Orbital Sciences Corporation in 2008. The NG-12 mission will be the first of at least six missions for the follow-on CRS-2 contract awarded in 2016.

“When I think back to when we first started this, looking ahead to what would be our last mission, seems like so long ago,” DeMauro said. “But here we are.”