Europe's second Automated Transfer Vehicle will carry more supplies, propellant and breathing air than its predecessor when it blasts off in December from French Guiana toward the International Space Station.

The second ATV's cargo carrier is in French Guiana for launch preparations. Credit: Arianespace

The program's partners have not officially settled on a target launch date, according to Nico Dettmann, the Johannes Kepler mission manager at the European Space Agency.

Mission planners must carefully thread the ATV between a spate of space shuttle flights, visiting Russian Progress and Soyuz vehicles, and a Japanese cargo mission.

The massive spacecraft, nicknamed Johannes Kepler, will ride an Ariane 5 rocket into orbit. The liftoff from the Guiana Space Center is in an instantaneous launch window.

It will reach the space station eight days later.

Arianespace is holding open the possibility of launching two commercial communications satellites in its December slot, in case the ATV is not ready for flight.

"We have to decide exactly what to do," said Jean-Yves Le Gall, Arianespace's chairman and CEO. "We have the further question of the launch window for the ATV because there are some docking windows to the space station. We will decide by the end of September what will be the sixth flight of the year."

The spacecraft was shipped to French Guiana in May from an Astrium factory in Bremen, Germany.

"The ATV is transported in three parts, which is the integrated cargo carrier, the spacecraft carrying the avionics and propulsion bays, and the separation system, which is basically the adapter for the Ariane 5," Dettmann said.

Dettmann said the cargo carrier and spacecraft bus should be mated by the end of September.

Crews have recovered from an earlier two-week delay in the start of the Ariane 5 launch campaign caused by slips in Arianespace's busy schedule of commercial flights this fall, according to Dettmann.

Officials added several upgrades to Johannes Kepler to increase its cargo capacity and address lessons learned on the ATV's successful first flight, which resupplied the space station in 2008.

Engineers designed lighter dry cargo racks to accommodate soft bags with supplies, saving about 50 kilograms, or 110 pounds, of weight on each rack, according to Dettmann.

The Ariane 5's solid rocket boosters will fly with welded connection joints, giving the launcher more capacity to the ATV's planned injection orbit, Dettmann said.

The sum of the rack and rocket improvements will boost the ATV's performance by about 650 kilograms, or 1,433 pounds.

In an interview with Spaceflight Now, Dettmann said teams corrected two glitches from the ATV's debut mission, dubbed Jules Verne, to ensure they do not happen again.

Engineers partially redesigned pressure regulators in the ATV's propulsion system after Jules Verne suffered pressure imbalance between two of its propellant tanks. The anomaly did not impact the mission, since the redundant pressurization system took over and the initially faulty propulsion chain was recovered.

"We are confident we will not run into that problem again," Dettmann said.

Insulation blankets on Johannes Kepler will have reinforced attachment points and improved internal venting, Dettmann said. Officials ordered the changes after some blankets became partially detached during the Jules Verne mission.

The second ATV mission will not duplicate a series of one-time tests conducted by Jules Verne, which approached the station over several demo days with increasingly ambitious objectives.

File photo of the first ATV approaching the International Space Station. Credit: NASA

"Those demonstrations are not manifested for ATV-2, and therefore ATV-2 has not only the full, but new and improved uplift capability," Dettmann said.

The performance-increasing design changes, plus fuel savings from deleted demonstration objectives on the second ATV flight, will permit Johannes Kepler to ferry a full load of propellant to the space station.

The ATV's engines will burn about 4,000 kilograms, or 8,800 pounds, of propellant to raise the station's altitude next spring after the final scheduled space shuttle flight in February and March.

The orbit boost will amount to about 40 kilometers, or 25 miles. The station will need fewer reboosts in the future when flying in the higher orbit, which subjects the complex to less drag.

If NASA adds an extra shuttle flight, it will have to reach the station in a higher orbit, meaning it will not be able to carry quite as much cargo as previous missions.

The STS-135 flight is penciled into NASA's manifest for launch in late June, after the ATV is scheduled to depart.

Johannes Kepler will also transfer 860 kilograms, or nearly 1,900 pounds, of hydrazine and nitrogen tetroxide propellants to the space station's Russian segment, Dettmann said.

Workers are packing 1,600 kilograms - more than 3,500 pounds - of dry goods into the ATV's pressurized cargo hold. The station's crew will unload the supplies after docking.

Johannes Kepler does not carry any water, but it will add 220 pounds of gas for the station's atmosphere.

Dettman said the mission costs between 400 and 450 million euros, or more than $500 million at today's exchange rates.

After four or five months docked with the station, Johannes Kepler will back away with the outpost's trash and burn up during re-entry into the atmosphere.

A third ATV is slated for launch in February 2012. Its service module and cargo carrier are being assembled in Bremen and Torino, Italy, respectively, Dettmann said.

At least two more ATVs are on the books for launch in February 2013 and February 2014.

A decision is expected by the end of this year on further production of ATVs and the next phase of a returnable version of the cargo ship. ESA is considering both options to continue servicing the space station beyond 2015.