A Northrop Grumman Cygnus supply ship departed the International Space Station Saturday after a three-month stay, heading off on the final phase of its mission to deploy a U.S. military tech demo payload and re-enter the atmosphere to dispose of 7,500 pounds of trash.

The unpiloted cargo freighter was unberthed from the space station’s Unity module early Saturday using the lab’s Canadian-built robotic arm. Ground controllers commanded the arm to position the Cygnus spacecraft below the station, then sent the order to release the cargo ship at 11:01 a.m. EDT (1601 GMT).

Snares at the end of the arm opened, allowing the Cygnus spacecraft to begin floating away. Thrusters on the Cygnus supply ship fired to propel the craft farther from the space station. Within a half-hour, Cygnus was on a safe trajectory away from the station, allowing ground teams at Northrop Grumman in Virginia to begin an extended mission for the spacecraft.

The Cygnus cargo ship, named the S.S. Ellison Onizuka after one of the astronauts who died on the space shuttle Challenger, arrived at the space station Aug. 12 with more than 8,000 pounds of supplies, equipment, and experiments. The freighter launched Aug. 10 on top of an Antares rocket from Wallops Island, Virginia.

The mission is Northrop Grumman’s 16th resupply flight to the International Space Station under contract to NASA.

Astronauts inside the space station unpacked the cargo delivered by the Cygnus spacecraft, then replaced it with trash tagged for disposal.

The Cygnus cargo ship’s extended mission will run through Dec. 15, when the spacecraft will perform a deorbit burn to reenter the atmosphere and burn up over the South Pacific Ocean.

Before its destruction, the spacecraft will deploy a small experimental payload for the U.S. military’s Space Development Agency and Missile Defense Agency.

The Prototype Infrared Payload, or PIRPL, experiment has collected data from a mounting fixture on the outside of the Cygnus spacecraft. Before the ship plunges back into the atmosphere, Cygnus will release the PIRPL payload to conduct standalone observations using its infrared sensor.

The infrared data will help engineers designing the next generation of missile tracking satellites. The technology demonstration will help future U.S. military satellites better detect and track hypersonic missiles, like the ones China and Russia have recently tested.

Northrop Grumman developed and flew the PIRPL payload on the Cygnus spacecraft under a $13.8 million contract from the Space Development Agency.

One of the final experiments of the Cygnus mission will be a test of heat shield technology using three small capsules stowed inside the Cygnus spacecraft.

When the Cygnus breaks apart during re-entry, the capsules will plunge deeper into the atmosphere protected by heat shields made of different types of materials.

Led by engineers at the University of Kentucky, the experiment will collect data from sensors embedded in each capsule’s heat shield. The measurements will be transmitted back to the science team via the Iridium satellite network.

The developers of the re-entry experiment say the data will help validate computer models used in spacecraft design.

“The Cygnus system has evolved from being just a cargo delivery service to a high performing science platform,” said Steve Krein, vice president of civil and commercial space in Northrop Grumman’s tactical space system business unit. “We continue to develop these capabilities to include the installation of environmental control systems and other upgrades to support the lunar orbiting Habitation and Logistics Outpost, or HALO (on NASA’s Gateway lunar space station).”

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