KENNEDY SPACE CENTER, Fla. — An Atlas 5 is ready to launch a Cygnus spacecraft to the International Space Station, resuming what NASA hopes is a regular series of cargo missions providing essential supplies and experiments to the station after two previous failures.

United Launch Alliance moved the Atlas 5 rocket, carrying an Orbital ATK Cygnus spacecraft, to the launch pad at Cape Canaveral, Florida, early Dec. 2. The rocket is scheduled to launch during a 30-minute window that opens at 5:55 p.m. Eastern Dec. 3.

Officials said in briefings here Dec. 2 that the major issue with the upcoming launch is the weather. Forecasts call for a 60 percent chance of acceptable weather at launch time Dec. 3 as a frontal system moves to the south, degrading to 40 percent should the launch slip to Dec. 4.

The U.S. Air Force meteorologist supporting the launch, though, was optimistic. “Overall, we’re looking at fairly favorable conditions,” said Todd McNamara, launch weather officer with the 45th Weather Squadron.

The launch will be the first time that Cygnus has flown on an Atlas 5, after previous missions used Orbital’s own Antares vehicle. Both Orbital and ULA officials said the process of integrating Cygnus on the Atlas, which started a year ago, has gone well.

“The process has gone very smoothly,” said Frank Culbertson, president of Orbital ATK’s Space Systems Group. “The teams have worked really well together, and it’s been quite impressive to see what they’re willing to do to keep this program going.”

Atlas 5 OA-4 rollout
The Atlas 5 carrying the Cygnus cargo tug leaves the Vertical Integration Facility to head to the launch pad at Space Launch Complex 41 at Cape Canaveral, Florida, Dec 2. Credit: SpaceNews/Jeff Foust

Vern Thorp, program manager for NASA missions at ULA, said the experience levels of Orbital and NASA helped the launch processing work despite this being the first time this spacecraft has flown on an Atlas. “The technical integration activity has gone very smoothly,” he said.

The Cygnus, flying a mission designated OA-4 by Orbital ATK, is carrying more than 3,500 kilograms of cargo for the station. That includes nearly 1,200 kilograms of crew supplies, topping up stockpiles of consumables there that, in some cases, have started to fall to low levels.

Of particular concern, said NASA ISS program manager Kirk Shireman, were levels of supplies for the station’s toilet that would run out in February without resupply. He said food supplies on the station would also drop to a “warning line” in February and would run out April 12 if no additional cargo missions visited the station.

“2015 has been a difficult year for ISS,” he said, referring to the loss of a Progress cargo spacecraft in April and a SpaceX Dragon spacecraft in June, as well as the loss of the previous Cygnus in October 2014. “So we’re looking forward to those supplies being replenished by the Cygnus.”

Cygnus is also carrying 1,000 kilograms of station hardware, including some spare parts that have also started to drop to low levels on the station. “We’ve been consuming some of our critical spares,” Shireman said. “We are below where we would like to be relative to our on-orbit hardware spares.”

Shireman said he hopes to gradually restore those levels over the next year as both Cygnus and Dragon resume cargo missions to the station. “I can’t emphasize enough how important it us on board ISS to us to have a regular cadence of resupply flights,” he said. “A year from now, if things go according to plan, we’ll be back in a very robust configuration.”

Besides crew supplies and spare parts, the Cygnus is also carrying nearly 850 kilograms of research payloads. Some of those are science experiments studying topics ranging from combustion to fluid dynamics, while others are small satellites that will be later deployed from the station.

One of those smallsats is a spacecraft developed by Los Alamitos, California-based NovaWurks called the Satlet Initial-Mission Proofs and Lessons, or SIMPL. The spacecraft, spun out of the U.S. Defense Advanced Research Projects Agency’s Phoenix program, is intended to test the ability to build satellites using mass-produced building blocks dubbed “satlets.”

SIMPL will be assembled on the station and later deployed, said Talbot Jaeger, chief technology officer of NovaWurks. SIMPL is designed to test the satlet technology that could then be scaled up to much larger spacecraft. “We’re loking for flexibility, speed, and low cost” with the satlet approach, he said.

A much simpler spacecraft also flying on Cygnus is STMSat-1, a single-unit cubesat developed by students at St. Thomas More Cathedral School in Arlington, Virginia. School principal Eleanor McCormack said the satellite is the first built by students at an elementary school.

STMSat-1 will carry a simple camera and amateur radio system to transmit images back to Earth. However, the real benefit of the spacecraft, McCormick said, is teaching students about spaceflight and how to overcome challenges during a project that started more than three years ago.

“We wanted the students to be able to see that things that are worthwhile sometimes take a long time,” she 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...