Sirangelo joined NASA last month as special assistant to the administrator and was tabbed to guide the agency's efforts to explore the lunar surface. Bridenstine said, however, that NASA's proposal for the "Moon to Mars Mission Directorate", which had support from the White House, was turned down by Congress.
"NASA proposed to the House and Senate a reorganization to establish a new mission directorate focused on a sustainable lunar campaign," Bridenstine said in a statement. "The proposal was not accepted at this time, so we will move forward under our current organizational structure within the Human Exploration and Operations Mission Directorate."
The mission was first announced in March to meet Vice President Mike Pence's goal of returning humans on the moon by 2024.
Sirangelo appeared with other NASA officials this week at an advisory council to discuss exploration plans. At the meeting, he said he'd been working on the plan to return to the moon, a mission he called "daunting." Also at the meeting, Bridenstine said NASA needs an additional $1.6 billion for the 2020 budget to reach the goal.
"Given NASA is no longer pursuing the new mission directorate, Mark has opted to pursue other opportunities. I want to personally thank Mark for his service and his valuable contributions to the agency," Bridenstine said.