Boca Chica, Texas (CNN Business) SpaceX's Crew Dragon capsule could be ready to fly NASA astronauts in three to four months. It would mark the first time humans have launched to orbit from US soil in almost a decade.

CEO and chief engineer Elon Musk told CNN Business' Rachel Crane that SpaceX is "going as fast as we can" to get the overdue spacecraft, which is designed to ferry astronauts to the International Space Station, ready for flight.

Jim Bridenstine, NASA's administrator, said in an interview on Monday that he is not confident in that timeline. The space agency will likely have to purchase more seats aboard Russian-made spacecraft in 2020, he said, to ensure US astronauts have continued access to the space station because of ongoing dealys with its Commercial Crew program, he said. That program includes Crew Dragon and a Boeing-built capsule, Starliner, which is also years behind schedule.

NASA asked the private sector to develop crew-worthy spacecraft to replace the Space Shuttle program after it retired in 2011. SpaceX was allotted $2.6 billion and Boeing was awarded $4.2 billion in 2014. NASA originally predicted both companies' spacecraft would be up and running by 2017.

SpaceX's Crew Dragon capsule flew an uncrewed demonstration mission in March, during which it briefly docked with the ISS. The company was expected to launch astronauts in July, but the craft exploded earlier in the year during a ground test of its emergency abort system.

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