WASHINGTON — NASA has added Orbital Sciences Corp.’s Antares rocket to the NASA Launch Services (NLS) 2 contract the agency awarded the Dulles, Va.-based company and several other launch providers in 2010.

The NLS 2 contract is an indefinite-quantity, indefinite-delivery contract that NASA uses to order launch services. An on-ramp provision allows new providers and launch vehicles to be added to the contract annually.

Orbital is developing the two-stage Antares — with NASA financial assistance — to launch the unmanned Cygnus space tug on cargo delivery missions to the international space station under a $1.9 billion NASA contract awarded in 2008. Orbital plans to conduct a hold-down test firing of the rocket’s first stage in late July or early August followed by a demonstration launch in August or September, Orbital officials told investors June 14.

Orbital’s space station resupply missions will be conducted on a commercial basis, outside the NLS 2 contract. Inclusion in NLS 2 contract puts Antares in the stable of vehicles eligible to compete to launch NASA scientific payloads provided they meet the agency’s reliability criteria.

Brian Berger is editor in chief of SpaceNews.com and the SpaceNews magazine. He joined SpaceNews.com in 1998, spending his first decade with the publication covering NASA. His reporting on the 2003 Space Shuttle Columbia accident was...