TEHRAN, January 22 (MNA) – Bill Nelson has stepped down as NASA administrator, ending a half-century of public service.Nelson and NASA Deputy Administrator Pam Melroy left the agency on Monday (January 20), the day that Donald Trump began his second term as president.

Trump has appointed Janet Petro, who most recently served as director of Kennedy Space Center (KSC) in Florida, as NASA's interim chief.

"As I leave public office today after 53 years, thank you for the great privilege of a lifetime of serving the people of our country.

I am humbled and grateful," Nelson said in a Monday X post.

Nelson, a member of the Democratic Party, began his US government career in 1972, when he was elected to the Florida House of Representatives.

He won a seat in the US House six years later, representing Florida's 9th congressional district.

The district is close to the state's famous Space Coast, which is home to both KSC and Cape Canaveral Space Force Station.

In January 1986, Nelson flew on the STS-61-C mission of the space shuttle Columbia, becoming the first sitting member of the US House to reach the final frontier.

The pilot of that flight was Charlie Bolden, who served as NASA chief during the Obama administration.

STS-61-C was also the mission immediately before the STS-51-L flight of the space shuttle Challenger, which ended in tragedy just 73 seconds after liftoff on January 28, 1986.

MNA/