NASA has been without a permanent leader for more than a year. Now the agency’s temporary leader is leaving, too.
In an email to the space agency’s employees on Monday, Robert M. Lightfoot Jr., the acting administrator, announced that he would retire on April 30.
Mr. Lightfoot said he was leaving “with bittersweet feelings,” but did not say why he was retiring.
“I cannot express enough my gratitude to the entire NASA team for the support during my career and especially the last 14 months as your acting administrator,” Mr. Lightfoot wrote.
Mr. Lightfoot’s impending departure could leave a vacuum at the top of NASA just as a revived National Space Council, which last existed more than 20 years ago, looks to revamp American space policy.
The council, chaired by Vice President Mike Pence, is to coordinate what various agencies, military and civilian, are doing in space. Two priorities are streamlining regulatory processes for space companies and returning astronauts to the moon.
The Trump administration’s latest budget proposal for NASA would end direct American financing of the International Space Station by 2025 and spur the development of commercial alternatives.
The previous administrator, Charles F. Bolden Jr., stepped down at the end of President Obama’s term. Mr. Lightfoot, who was associate administrator, the third-highest ranking position at NASA, took over as acting administrator.
In September, President Trump nominated Representative Jim Bridenstine, Republican of Oklahoma, to be the next administrator. But the Senate has yet to vote to confirm Mr. Bridenstine.
All 49 Democrats in the Senate appear unified in opposition, in part because Mr. Bridenstine gave a speech disparaging climate change several years ago. Senator Marco Rubio, Republican of Florida, also has expressed doubts about Mr. Bridenstine.
The space agency’s No. 2 position, deputy administrator, is vacant, and the Trump administration has yet to nominate anyone to fill the post. Steve Jurczyk, formerly the associate administrator for space technology, was named in late February to temporarily fill Mr. Lightfoot’s previous job.
NASA is also lacking a chief of staff.
Still, the agency continues to explore the cosmos. Next month, it is scheduled to launch the Transiting Exoplanet Survey Satellite, or Tess, a space telescope that is to search for planets around other stars.
The InSight spacecraft is due to launch in May for Mars, and the Parker Solar Probe is expected to begin a yearslong mission to study the sun in July.
In August, Boeing and SpaceX both plan to perform their first tests of new capsules that are to carry NASA astronauts into orbit, and the Osiris-Rex spacecraft will rendezvous with an asteroid, Bennu, after a two-year journey.
Mr. Lightfoot’s 406-day term as acting administrator is by far the longest NASA has operated without a permanent leader, eclipsing the 176 days that passed at the start of the Obama administration before Mr. Bolden was confirmed.
Senator Bill Nelson of Florida, a Democrat who has led opposition to Mr. Bridenstine’s appointment, praised Mr. Lightfoot in a statement. “The country owes Robert a debt of gratitude for his many years of outstanding service and leadership at NASA,” Mr. Nelson said.
He also alluded to the impasse over Mr. Bridenstine. “Longer term, the White House needs to nominate a space professional for NASA administrator who will actually garner strong bipartisan support,” Mr. Nelson said. “The current nominee doesn’t have the votes.”