WASHINGTON — For the second time in less than four months, an Orbital ATK Cygnus cargo spacecraft is set to launch to the International Space Station on an Atlas 5, carrying more than three tons of supplies and science investigations.

Launch of the Cygnus on a mission designated OA-6 is scheduled for 11:05 p.m. Eastern March 22 from Cape Canaveral, Florida, at the beginning of a half-hour launch window. Weather forecasts predict a 90 percent chance of acceptable weather at launch time.

At a March 21 press conference at NASA’s Kennedy Space Center, officials reported no issues with either the Cygnus spacecraft or the United Launch Alliance-built rocket. “It’s all gone very smoothly,” said Frank Culbertson, president of Orbital ATK’s space systems group.

The Cygnus is carrying 3,279 kilograms of cargo to the station, split roughly evenly among crew supplies, vehicle hardware, and other items, including science investigations. That cargo will support about 250 research investigations planned for the station in the coming months, according to NASA.

Loaded on the Cygnus are a variety of experiments and related equipment for the station. Among them are experiments to test the behavior of particles of regolith in low-gravity environments, like the surface of asteroids, and an adhesive technology known as “Gecko Grippers.” The Cygnus also carries an advanced 3-D printer called the Additive Manufacturing Facility, developed by a California-based company, Made In Space.

The Cygnus itself will be used as an experiment platform near the end of its mission. The spacecraft’s service module is fitted with a satellite deployer from NanoRacks that will deploy several cubesats after leaving the station and before it reenters the atmosphere.

“This expands our capability,” Michael Lewis, chief technology officer of NanoRacks, said at a March 21 press conference. Launching from the Cygnus directly limits the use of the airlock in the station’s Kibo module, from which cubesats have previously been deployed and which is in high demand. Launching from the Cygnus, he added, frees up cubesats to use propulsion systems that might pose safety issues if transported inside of the station itself.

The Cygnus, after unberthing, will host an experiment known as Saffire-1 to test the flammability of materials in microgravity. Doing the experiment on the Cygnus, rather than on the station itself, will allow scientists to use a larger fire: the fabric sample that will be ignited in the experiment is about one meter long. “What we want to do is start to get to a more dangerous fire if it were to occur in a spacecraft,” said experiment co-investigator Gary Ruff.

The fire will be controlled and is designed to stay within its containment vessel so that it does not pose a risk to Cygnus itself. “There is no chamber big enough on ISS to burn something this large,” Ruff said, explaining why the experiment will be done on Cygnus. In addition, “the piece we’re not doing on Cygnus that we would definitely have to do on ISS is cleaning up the mess.”

The supplies on the Cygnus will further restock consumables like food on the station as it largely recovers from the loss of three cargo missions in an eight-month period from October 2014 through June 2015. “The ISS is in really good shape consumables-wise,” said Kenneth Todd, NASA’s ISS operations integration manager. The station, he said, has stockpiles of its most critical consumables through at least December.

This mission is the second time Orbital ATK has flown a Cygnus on an Atlas 5, after a mission launched Dec. 6. That mission was the first Cygnus flight since an October 2014 failure of an Antares rocket seconds after liftoff from the Mid-Atlantic Regional Spaceport in Virginia.

Orbital ATK plans to resume launching Cygnus spacecraft on a new version of the Antares rocket this summer. Culbertson said a static fire test of the re-engined Antares first stage is planned for later this spring. “We’ll be ready early this summer for a launch,” he said, with an exact date depending on when NASA wants to fly the next Cygnus mission.

However, Culbertson left the door open to future Cygnus launches on Atlas vehicles. Orbital ATK’s Commercial Resupply Services 2 contract, awarded by NASA in January, includes options for Cygnus launches on both Atlas and Antares launch vehicles. “It’s really up to NASA in terms of what kinds of missions they order in the future under the new contract,” he said.

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...