Four-time astronaut Charles Bolden resigned as NASA administrator on Jan. 20, 2017, leaving the space agency after more than seven years on the job. Since then, a former director of the Marshall Space Flight Center in Alabama, Robert Lightfoot, has served as interim director. He has held this post now for 315 days, or nearly 11 months.

According to an analysis of the gaps between administrators at the space agency, NASA has never gone this long without a formal administrator. Beginning with T. Keith Glennan, in 1958 and running through the term of Charles Bolden six decades later, there have been ten transitions between NASA administrators. The average gap between administrators has been 3.7 months.

There are two past analogs for the current situation, when an administrator for the president of one political party resigned on the day a new president from the other party took office. This occurred in 1981, when Robert Frosch resigned upon President Carter’s departure, and again in 2009, when Michael Griffin resigned upon George W. Bush’s departure. In each case, the gap between resignation and Senate approval of a new administrator was less than six months, 170 and 176 days, respectively.