Skip to main content

Space History Photo: Harold Geisler Takes Plum Brook Reactor Critical

space history, radiation research, Plum Brook research reactor
In June 1961, the Plum Brook reactor goes critical for the first time. (Image credit: NASA.)

In this historical photo from the U.S. space agency, Harold Geisler takes the Plum Brook reactor critical for the first time on the evening of 14 June 1961. This first self-sustaining chain reaction was conducted at very low power.

It wasn't until the following April that the reactor reached its full potential of sixty megawatts. By July 1963, the reactor had completed its first experimental cycle while critical.

For more information browse the Plum Brook Facility Page.

Each weekday, looks back at the history of spaceflight through photos (archive).

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at:

The National Aeronautics and Space Administration (NASA) is the U.S. government agency in charge of the civilian space program as well as aeronautics and aerospace research.