Kathy Lueders, manager of NASA's commercial crew program, said the initial launches without astronauts are "a great dry run for not only our hardware, but for our team to get ready for our crewed flight tests".
The agency's Commercial Crew Program has been working with SpaceX "throughout the month of January" to make sure it is "ready to learn critical information that will further help us to fly our crews safely", officials said.
The uncrewed demonstration launch of Crew Dragon is now set for March 2 and Starliner will perform a similar launch no earlier than April.
SpaceX's "Crew Dragon" capsule will be used for both launches, the second of which will send two USA astronauts to the International Space Station. A crewed test flight, with NASA astronauts Mike Fincke and Nicole Mann, and Boeing astronaut Chris Ferguson, is scheduled for no earlier than August.
SpaceX had been targeting February 23 for Crew Dragon's shakeout cruise to the ISS, an uncrewed flight called Demo-1. Astronauts haven't launched to orbit from American soil since July 2011, when NASA retired its space shuttle fleet.
"These adjustments allow for completion of necessary hardware testing, data verification, remaining NASA and provider reviews, as well as training of flight controllers and mission managers", they added. A final launch date was scheduled for the first half of March. The unpiloted capsule will execute an autonomous rendezvous with the space station, moving in for docking the day after launch. Recovery crews will haul the craft to shore for detailed post-flight examination. The rocket performed a static fire test on the pad January 24 that the company said was successful.
NASA announced in August past year the names of the first four astronauts who will fly the Crew Dragon module in 2019. Boeing plans to run this test in May, and SpaceX will perform its version in June. The Starliner will blast off from pad 41 at the Cape Canaveral Air Force Station, riding into space atop a United Launch Alliance Atlas 5 rocket.
No one will be on board for the crew Dragon's inaugural test flight to the orbiting outpost. Unlike the Crew Dragon, the Starliner is created to land in the western United States using parachutes and airbags.
We're going to have to wait a bit longer to finally see astronauts take a ride aboard new spacecraft from SpaceX and Boeing. NASA also wants to have the Crew Dragon approved to take astronauts to the ISS by late 2019.
If all goes well, operational crew rotation flights could begin well before the end of the year.