Elon Musk, chief executive officer of Space Exploration Technologies Corp. (SpaceX) and Tesla Inc., speaks during an event at the SpaceX launch facility in Cameron County, Texas, U.S., on Saturday, Sept. 28, 2019.

SAN FRANCISCO — In a conversation with the top U.S. Air Force officer on space research and acquisition, SpaceX CEO Elon Musk on Tuesday explained why his company is on an aggressive timeline to develop a massive rocket capable of launching and landing multiple times, like an commercial aircraft.

"With respect to space, I think there's really just one problem, which is a fully and rapidly reusable orbital rocket. This is the holy grail," Musk said, speaking with Lt. Gen. John Thompson at the Air Force's Space Pitch Day event.

"SpaceX has made some progress in reusing the booster," Musk said. But that's still only part of the rocket. As Musk said, "It's absolutely profound to have a reusable rocket."

"A giant reusable craft costs much less than a small expendable craft," Musk said.

Musk described Starship, the next-generation rocket SpaceX is developing, as the key to fully reusing a rocket. He said Starship is a "pretty ambitious" project, as it represents the culmination of Musk's vision for SpaceX: Capable of sending people to-and-from the moon and Mars.

SpaceX President Gwynne Shotwell said at a recent event that SpaceX wants to have Starship in orbit next year. " We want to land it on the moon before 2022 with cargo and with people shortly thereafter," she said.

If SpaceX can repeatedly launch and land its Starship rocket, it could make space travel more akin to air travel, with only minor maintenance needed between flights and fuel as the main cost for an airplane. A SpaceX Falcon 9 rocket comes with a price tag of $62 million per launch and up. But, if Starship can achieve being a fully reusable rocket, Musk touted the rocket's $900,000 fuel cost as the significant cost for its launch -- a fraction of today's launch costs.

"It's the thing that needs to be made," Musk said.