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NASA has ordered four additional launches to deliver cargo to the International Space Station in 2017 — three from SpaceX and one from Orbital ATK — to cover the research lab’s logistics needs until a new set of resupply contracts take effect.

The extra missions for SpaceX and Orbital ATK will serve as a bridge between the contractors’ current contracts and new commercial cargo deals that will cover resupply missions launching from 2018 through at least 2020.

SpaceX and Orbital ATK won Commercial Resupply Services contracts from NASA in December 2008, covering 12 cargo deliveries by SpaceX’s Dragon spacecraft and eight missions with Orbital ATK’s Cygnus supply ship.

A NASA spokesperson said the space agency has extended the CRS contract one year, giving SpaceX and Orbital ATK until the end of 2017 to complete the extra missions to bring provisions, food, clothes, experiments and spare parts to the 450-ton complex more than 250 miles above Earth.

“NASA has ordered three additional flights with SpaceX in the extension period,” said Stephanie Schierholz, a NASA spokesperson. “NASA has ordered one additional flight with Orbital in the extension period. This is based on the projected needs of the ISS program for cargo upmass, return and disposal and the unique capabilities of each contractor.”

Shierholz declined to release the value of the contract modifications, saying the data is sensitive.

SpaceX and Orbital ATK’s original contracts, which included mechanisms to add more missions, had “not-to-exceed” values of $3.1 billion each. That value does not change with the extra missions, Schierholz said.

The new launch orders give SpaceX 15 resupply missions under the contract.

Orbital ATK lost a Cygnus supply ship during an explosive launch mishap moments after liftoff from Virginia in October, forcing the company to redesign its Antares rocket for a new engine. The next Cygnus cargo carrier is due for launch from Cape Canaveral in October on a United Launch Alliance Atlas 5 rocket, then Orbital ATK plans to resume launches on the Antares booster in March 2016.

The Atlas 5 rocket can lift more cargo into orbit than the Antares launcher — allowing officials to use more of the Cygnus spaceship’s expansive internal volume — and Orbital ATK says it can now meet its contractual obligations to NASA with seven flights.

NASA required each contractor to deliver at least 20 metric tons, or about 44,000 pounds, of cargo to the space station.

The new mission launching in 2017 gives Orbital ATK eight flights, including the failed launch last year.

NASA is conducting an open competition for a second round of Commercial Resupply Services (CRS 2) contracts. Officials plan to select winners in June.

Agency officials are expected to choose at least two contractors to ensure the space station has redundant supply chains in case one company runs into problems.

The competition is packed, with Orbital ATK, Boeing Co., Sierra Nevada Corp. and Lockheed Martin Corp. confirming they submitted bids. SpaceX is also believed to be in the running, but company officials have not confirmed their participation.

Boeing’s CST-100 crew capsule in development to transport astronauts to and from the space station could be outfitted to carry cargo on round-trip missions. Sierra Nevada is developing the Dream Chaser space plane, but it lost a NASA contract to ferry crews to Boeing and SpaceX.

Lockheed Martin told reporters this week it plans to unveil details of its bid to resupply the space station March 12.

Follow Stephen Clark on Twitter: @StephenClark1.