Kenneth John Frost (October 3, 1934 - August 5, 2013) was a pioneer in the early space program, designing and flying instruments to detect and measure X-rays and gamma-rays in space, primarily from the Sun. He was the first to suggest the use of an active scintillation shield operated in electronic anticoincidence with the primary detector to reduce the background from cosmic ray interactions, an innovation that made sensitive hard X-ray and gamma-ray astronomy possible.