SpaceX launched a reduced two-man crew on a flight to the International Space Station Saturday, along with supplies and a pair of empty seats for two Starliner astronauts waiting to hitch a ride home in February after an unexpected eight-and-a-half-month stay in orbit.

The SpaceX Falcon 9 rocket roared to life and blasted off from pad 40 at the Cape Canaveral Space Force Station at 1:17 p.m. EDT, climbing away on a northeasterly trajectory directly into the plane of the space station's orbit.

Monitoring the automated ascent from inside the Crew Dragon "Freedom" were commander Nick Hague, a veteran NASA astronaut, and Russian cosmonaut Alexander Gorbunov, making his first flight.

Crew Dragons normally launch with four crew members, but two Crew 9 astronauts -- Stephanie Wilson and Zena Cardman, the original commander -- were removed from the flight in August to free up seats that will be used by Starliner commander Barry "Butch" Wilmore and pilot Sunita Williams when the Crew Dragon returns to Earth in February.

The mission initially expected to last eight to 10 days, but multiple helium leaks in the Starliner's propulsion system, along with degraded thrust in five maneuvering jets, eventually led to a NASA decision to bring the spacecraft down earlier this month without its crew.

Instead, NASA managers opted to launch the Crew 9 Dragon with just two of its original crew members to enable the ship to bring Wilmore and Williams back to Earth at the end of its mission in February. By the time they land aboard the Crew 9 capsule around Feb. 22, they will have logged more than 262 days in space.

Some have called the Crew Dragon flight a "rescue" mission. But Wilmore and Williams have always had a way home, first aboard their own spacecraft, then aboard the Crew 8 Dragon and, after docking Sunday, aboard the Crew 9 Dragon. NASA chose the latter option as the least disruptive to the ISS crew rotation schedule.

The transition from a four-person crew to just two presented a different sort of challenge for Hague and Gorbunov — as well as for Wilmore and Williams — who never trained for a flight aboard a Crew Dragon.

"We're going to launch as a two-person crew, and then we're going to land as a four-person crew," Hague said. "And one of the unique challenges of that is, how do we integrate the other two crew members into the Dragon operations when they've had very minimal Dragon training before they launched?

"The teams on the ground have helped not only get us ready, but they've already started helping Butch and Suni train to understand what they're going to need to do inside of inside of the Dragon. That's going to be top priority when we get there, (helping) them understand what they're going to need to do to operate as part of the Crew 9 crew.