Walker was the first non-career, industry-sponsored astronaut, serving as payload specialist on Space Shuttle missions STS-12 (41-D) in September 1984; STS-16 (51-D) in April 1985; and STS-23 (61-B) in November 1985. On those flights, Walker operated equipment designed by McDonnell Douglas Astronautics Company for it's electrophoresis biotechnology commercialization program (EOS) and accumulated 20 days and 8.2 million miles of space flight experience.

The EOS device, developed under a joint agreement between McDonnell Douglas and NASA , produced large, pure quantities of pharmaceuticals when operated in the weightlessness of space. As chief test engineer of the EOS program, Walker was extensively involved with the laboratory development and space flight test of the EOS device. Walker had also been responsible for training NASA astronauts in their earlier operation of the EOS device.

Walker, who is presently Senior Specialist for Advanced Space Programs Development at The Boeing Company, joined McDonnell Douglas in 1977 (McDonnell Douglas was acquired by Boeing in 1997). His initial assignment was that of test engineer on the aft propulsion subsystem for the Space Shuttle orbiters. Currently in Washington, D.C., Walker is supporting Boeing in technical marketing and policy issues. Walker has been a member of an independent national space policy review project and served on a National Research Council space applications board. He has also served on several government and university research center panels. Walker is currently an advisor to the Challenger Center for Space Science Education.

A native of Bedford, Indiana, Walker received his undergraduate degree in aeronautical and astronautical engineering from Purdue University in 1971. He was awarded an honorary doctor of science from St. Louis College of Pharmacy in 1985. Prior to joining McDonnell Douglas, Walker was a project engineer with the Naval Sea Systems Command working on computer-controlled manufacturing systems, a design engineer for Bendix Aerospace and, previous to that, an engineering technician and forest fire fighter with the U.S. Forest Service.