Posted: Sun, Mar 18, 2018, 11:20 AM ET (1520 GMT)

Robert Lightfoot, NASA's acting administrator for more than a year, will retire at the end of April. Lightfoot announced his retirement plans Monday, saying he was leaving the agency after nearly three decades with "bittersweet feelings." Lightfoot has been associate administrator, the highest ranking civil service position at the agency, since 2012, and took over as acting administrator at the beginning of the Trump administration. The nomination of Jim Bridenstine for NASA administrator remains stalled in the Senate.