Launch of the Orbital Sciences Corp. Antares liquid-fueled rocket on April 21 gives NASA a second U.S.-owned vehicle to use in resupplying the International Space Station, vindicating a commercial approach that has been in play through two presidential administrations.

The 5 p.m. liftoff followed two previous launch attempts last week that had to be scrubbed due to uncooperative weather over the new launch pad at the Mid-Atlantic Regional Spaceport on Wallops Island, Va. Ten minutes after leaving the pad, the rocket placed an 8,380-lb. (3,800-kg) instrumented dummy version of Orbital Sciences’ Cygnus cargo vehicle into orbit. An operational Cygnus is packed with station supplies and ready to launch to the ISS this summer if the inaugural flight goes as planned.

Although President Barack Obama terminated the Constellation program of human exploration vehicles that NASA started developing under his predecessor, he retained the $500 million Commercial Orbital Resupply Services (COTS) effort launched under President George W. Bush.

SpaceX already has completed its COTS development with the Falcon 9 rocket and Dragon capsule, and is delivering cargo to the station under its follow-on Commercial Resupply Services (CRS) contract.

If Orbital Sciences can deliver a demonstration load with its Cygnus cargo vehicle later this year, it can draw its final COTS payment and begin resupplying the station under its own eight-flight, $1.9 billion CRS contract. Essentially, NASA will have spent $288 million on developing the Antares/Cygnus stack.

SpaceX designed its Dragon from the beginning to carry crew, and is making the necessary modifications to its cargo variant under a separate NASA commercial crew development program established along the same lines as COTS. Two other companies — Boeing and Sierra Nevada — are developing crew vehicles with NASA seed money, and another — Blue Origin — is paying its own way with NASA technical support. Meanwhile, Orbital Sciences decided to focus on cargo and not enter the crew-vehicle arena, marketing Antares to government and commercial customers as a replacement to the retiring Delta II.

And while Cygnus can’t return into the Earth’s atmosphere, Orbital already has a NASA contract to use a future Cygnus as a free-flying automatic laboratory for potentially dangerous combustion experiments after it delivers its load to the ISS, and hopes to sell other Cygnus vehicles for similar uses.