SpaceX envisions an initial test of the upgraded Falcon 9 first stage’s “fly back” capabilities later this year as part of the third International Space Station Dragon mission launched under the company’s NASA Commercial Resupply Services (CRS) agreement, CEO and chief designer Elon Musk told a March 28 teleconference.

The Hawthorne, Calif.-based launch services provider will attempt a propulsively controlled landing in the Atlantic Ocean following the launch of a mission from Cape Canaveral Air Force Station, Fla., tentatively set for late September. SpaceX is probably a year and several attempts away from returning a nine-engine Falcon 9 first stage to a soft landing at the Florida launch site with deployment of landing legs.

“I really want to emphasize that we don’t expect success in the first several attempts,” said Musk, who joined NASA officials to discuss the positive March 26 conclusion of the company’s CRS-2 mission with a Dragon capsule splashdown and recovery in the Pacific off the coast of Baja, California. “Hopefully, next year with a lot more experience and data we would be able to return the first stage to the launch site, deploy landing legs and do a propulsive landing.”

The CRS-2 mission, launched March 1, delivered 2,090 lb. of internal and external cargo to the six-person orbiting research lab and returned with 3,256 lb. of frozen medical specimens, a range of other research gear and unneeded equipment, according to the company’s final mission accounting.

Musk pointed to a subtle design change and a lapse in qualification testing as the cause of three sticky check valves in the Dragon thruster system that prompted a one-day delay in the supply vessel’s scheduled March 2 rendezvous with the space station. All three valves were forced open with the rapid uplink of a software change that increased pressure in the system.

SpaceX was not made aware of the design change by its supplier, and while company’s engineers conducted a pre-mission low-pressure functionality test of the hardware, they elected to skip a high-pressure test that might have revealed the problem, he said.

“It was kind of the spacecraft equivalent of the Heimlich maneuver that got the valve unstuck. It was definitely a worrisome time,” Musk said. “Now, obviously [we] and the supplier are extremely sensitive to even nuanced changes.”

SpaceX has been testing a prototype of its Falcon 9 fly-back booster system called Grasshopper at the company’s McGregor, Texas, proving ground. If early testing of the concept works on an upgraded version of the Falcon 9, SpaceX could attempt a first-stage Florida launch site landing in mid-2014, according to Musk.