Gerstenmaier was born in Akron, Ohio, in September 1954 and graduated from East High School in 1973. As a teenager he followed the early space programs of Mercury, Gemini, and Apollo. He had early dreams of being a test pilot, and after high school, enrolled at the United States Naval Academy. After seeing so many pilots returning from the Vietnam War, he thought he may not get a chance to fly, and chose to reconsider his path. He transferred to Purdue's School of Aeronautics and Astronautics, hoping to get into flight via academics. During his time at Purdue, Gerstenmaier found a great interest in space technology, and chose to focus on this area for his career.
Gerstenmaier graduated with a bachelor of science in aeronautical engineering in 1977, and joined the Lewis Research Center (now called the John Glenn Research Center) in Ohio, beginning his career with NASA. Initially doing research with supersonic wind tunnels, developing air data curve information used during entry on the Space Shuttle. Gerstenmaier continued his education, obtaining his master's degree in mechanical engineering at the University of Toledo in 1981.
In 1980, Gerstenmaier moved to Houston, Texas, to work at the Johnson Space Center, researching propulsion related to the Space Shuttle, and was involved in the earliest phases of the International Space Station design. In 1984, he was a semi-finalist in the selection for NASA Astronaut Group 10. In 1988, he first served as manager of Space Shuttle Program Integration, and then went on to serve as head of the Orbital Maneuvering Vehicle Operations Office. Following that, he became Director of Space Shuttle and Space Station Freedom Assembly Operations, and was named Chief of the Projects and Facilities Branch of the Flight Design and Dynamics Division.
In 1992, Gerstenmaier was given a fellowship from NASA to obtain his doctorate degree from Purdue, and in 1992 and 1993, he completed course work for a doctorate in dynamics and control, with a minor in propulsion at Purdue University. Of the time away from NASA, he said, "It was the most humbling experience of my life."
In 1995, Gerstenmaier returned to NASA as the Shuttle/Mir Program Operations Manager, and was the liaison to the Russian Space Agency for operations and protocols. For the first half of 1996, he was stationed in Russia to support astronaut Shannon Lucid, who spent six months aboard Mir.
In December 2000, Gerstenmaier was named Deputy Manager of the International Space Station Program. In 2002, Gerstenmaier was named Manager of the International Space Station Program. Mike Suffredini replaced Gerstenmaier as the International Space Station Program manager.
Gerstenmaier current position - Associate Administrator for Human Exploration and Operations .
As part of his job, Gerstenmaier made the final decision in September 2014 to not select Dream Chaser in the fourth phase of the Commercial Crew Development program—after the SNC Dream Chaser had been selected as one of the contract award recipients in each prior phase of the program—due to lack of maturity. SNC filed a protest to the US Government Accountability Office (GAO) alleging "a high-ranking agency official [had] opted to rank Boeing’s proposal higher than a previous panel of agency procurement experts." More specifically, Sierra Nevada asserted in their filings with the GAO that Gerstenmaier may have "overstepped his authority by unilaterally changing the scoring criteria" for the contract award. On January 5, 2015, the GAO denied SNC's protest and disagreed with the company's arguments about NASA's evaluation, finding "no undue emphasis on NASA’s consideration of each offeror’s proposed schedule, and likelihood to achieve crew transportation system certification not later than 2017." The GAO also noted that, contrary to SNC's assertions, the RFP did advise all parties their proposals would be evaluated against a goal of certification by the end of 2017.
Gerstenmaier has twice been awarded the Aviation Week and Space Technology's Laureate Award for "Outstanding Achievement in the Field of Space", as well as three NASA Certificates of Commendation, two NASA Exceptional Service Medals, a Senior NASA Outstanding Leadership Medal, and the Presidential Rank Award for Meritorious Executives.
In 2003, he received the Presidential Rank Award for Meritorious Executives. Also that year he received the Outstanding Aerospace Engineer Award, Purdue University.
In 2004, Gerstenmaier was selected as a finalist for the Service to America Medal, for "Leading the efforts to continue the safe operation of the International Space Station in the absence of the Space Shuttle, allowing continued research and preservation of its unique capabilities for the future."
In 2006, the Huntsville National Space Club awarded him the Von Braun Award.
In 2007, The Federation of Galaxy Explorers honored Gerstenmaier with the 2007 Space Leadership Award, and Purdue University honored him with the Distinguished Alumni Award, "For outstanding accomplishments in a career dedicated to the human exploration of space and international cooperation in space." In November 2008 he was honored again at Purdue as an Old Master in the 2008 Old Masters Program.
Gerstenmaier received the Rotary National Award for Space Achievement's National Space Trophy in 2010, Space Transportation Leadership Award, 2011, the 2011 AIAA von Braun Award for Excellence in Space Program Management and the AIAA von Karman Lectureship in Astronautics in 2012.