A NASA executive tasked with leading the strategy to return U.S. astronauts to the moon has stepped down just six weeks after his appointment.

Mark Sirangelo was tapped in April as special assistant to NASA Administrator Jim Bridenstine James (Jim) Frederick BridenstineNASA publishes Artemis plan to land first woman, next man on moon NASA is in the market for moon rocks Overnight Defense: Trump hosts Israel, UAE, Bahrain for historic signing l Air Force reveals it secretly built and flew new fighter jet l Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' MORE, but he is leaving the agency after NASA's proposal of a new organizational structure to support the lunar campaign was not accepted by Capitol Hill.

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Bridenstine announced late Thursday that because NASA is "no longer pursuing the new mission directorate," Sirangelo "has opted to pursue other opportunities."

"We are exploring what organizational changes ... are necessary to ensure we maximize efficiencies and achieve the end state of landing the first woman and next man on the Moon by 2024," Bridenstine said in a statement obtained by The Hill.

"I want to personally thank Mark for his service and his valuable contributions to the agency," Bridenstine added.

Vice President Pence said in March that the administration is committed to landing astronauts on the moon within five years, marking the administration’s most concrete timeline to the lunar surface.

President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE also announced earlier this month that his budget would include an additional $1.6 billion for NASA, saying the U.S. is "going back to the Moon, then Mars."

Also on Thursday, NASA announced a $375 million contract to Maxar Technologies to develop power and propulsion capabilities for the lunar mission.

Updated at 8:43 a.m.