The first manned flight into orbit for SpaceX’s new Crew Dragon astronaut capsule will be held in 2020, if upcoming tests prove successful.

NASA chief Jim Bridenstine said on Thursday that successful development of the capsule was key to achieving NASA’s top priority - the resumed “launching of American astronauts on American rockets from American soil” for the first time since the space shuttle program ended in 2011.

NASA believes SpaceX is getting the Crew Dragon project back on track following an explosion during a ground test in April and technical challenges with its re-entry parachute system.

NASA and SpaceX had previously aimed to launch the Crew Dragon on an initial test flight carrying two astronauts to the International Space Station in 2019.

The revised time line hinges on a series of system tests that SpaceX hopes to conduct by year’s end. These include a high-altitude test of an in-flight abort system designed to propel the crew capsule to safety in the event of a rocket failure on the way to orbit.

The schedule also includes at least 10 more mid-air “drop tests” to gauge the resilience and performance of parachutes used to slow the capsule’s descent into the ocean after it re-enters the atmosphere from space.

The National Aeronautics and Space Administration is paying commercial launch companies SpaceX and Boeing Co $6.8 billion to build rocket-and-capsule systems enabling NASA to resume human space travel with U.S.-made hardware.

SpeceX's Elon Musk said overcoming problems with re-entry parachutes had proved especially challenging.

“It’s a pretty arduous engineering job to get the parachutes right,” Musk said, declaring that Crew Dragon’s parachutes will be at least twice as safe as those used during NASA’s Apollo moon missions.

He expected that “testing will be complete and hardware at the Cape (Canaveral) by the end of December.”

The top executive for Boeing’s rival Starliner program, John Mulholland, said on Wednesday that its own key test of an abort system was slated for Nov. 4, while its unpiloted orbital test flight was set for Dec. 17. Under that time frame, the first Starliner manned mission is all but certain to slip into 2020.