UPDATE 1-US could advance SpaceX license as soon as October after rocket exploded in April

(Adds more details, background on FAA process)

By David Shepardson

WASHINGTON, Sept 13 (Reuters) -

The acting head of the Federal Aviation Administration said on Wednesday the agency could advance a launch license as early as next month for the SpaceX Starship rocket after a prior one exploded following a test launch in April.

"We're working well with them and have been in good discussions. Teams are working together and I think we're optimistic sometime next month," acting FAA Administrator Polly Trottenberg told reporters on the sidelines of a conference.

SpaceX would still need a separate environmental approval from the U.S. Fish and Wildlife Service before a launch. Trottenberg did not say how long that might take.

The FAA last week concluded a technical investigation into SpaceX's April test launch of its Starship rocket, saying the company must implement dozens of corrective measures.

The April 20 launch of SpaceX's Starship Super Heavy rocket from Texas pulverized its launchpad upon successful liftoff and ascended 25 miles (40.23 km) before exploding roughly four minutes into its flight, as it was attempting a crucial demonstration to reach space for the first time.

The FAA cited "multiple root causes" of the Starship failure and 63 corrective actions to take before launching the rocket again, including hardware changes to prevent leaks and fires and reinforcing the rocket's launchpad to prevent a storm of kicked up debris and sand.

"The closure of the mishap investigation does not signal an immediate resumption of Starship launches at Boca Chica," the agency said last month, referring to SpaceX's sprawling Starship launch site in south Texas.

The FAA probe's closure puts SpaceX one step closer to getting Starship in space for the first time - a major, long-sought testing milestone before the company can use the reusable rocket for commercial satellite missions and human landings on the moon for NASA.

Later on Friday, SpaceX's CEO and founder Elon Musk asked the FAA "what are the 63 corrective actions?" in a post responding to the agency's statement.

In line with FAA regulations, Musk's space company led the Starship investigation and largely created the list of 63 corrective actions for the FAA to approve. The agency requires SpaceX complete those actions before it can obtain a new Starship launch license.

SpaceX must obtain a modified FAA license to launch, which entails a sometimes-lengthy review of the Starship's flight trajectory, accident probabilities and other factors affecting nearby public safety. (Reporting by David Shepardson Editing by Chris Reese and David Gregorio)