Michael Landon Gernhardt (Ph.D.) (born May 4, 1956, in Mansfield, Ohio) is a NASA astronaut and manager of Environmental Physiology Laboratory and principal investigator of the Prebreathe Reduction Program (PRP) at the Lyndon B. Johnson Space Center.

He enjoys running, swimming, flying, fishing, and scuba diving. His father, George M. Gernhardt is deceased. His mother, Suzanne C. Winters, resides in Whitestone, Virginia.

From 1977 to 1984, Gernhardt worked as a professional diver and project engineer on a variety of subsea oil field construction and repair projects around the world. He has logged over 700 deep sea dives and has experience in air, mixed gas, bounce bell and saturation diving. During his diving career Gernhardt attended graduate school at the University of Pennsylvania and developed a new theoretical based on tissue gas bubble dynamics. He then participated in the development and field implementation of a variety of new decompression tables. From 1984 to 1988, Gernhardt worked as Manager and then Vice President of Special Projects for Oceaneering International. During this time he led the development of a telerobotic system for subsea platform cleaning and inspection as well as a variety of new diver and robot tools. In 1988 he founded Oceaneering Space Systems, a company formed to transfer subsea technology and operational experience to the ISS program. From 1988 until his selection by NASA in 1992, he worked on the development of new astronaut and robot-compatible tools for performing maintenance on Space Station Freedom. He also worked on the development of new portable life support systems and decompression procedures for extra-vehicular activity.