the project's design and planning, dividing the work between them. Carpenter had training in airborne electronics and celestial navigation, so he assumed responsibility for the spacecraft's communications and navigation systems. Grissom had a degree in mechanical engineering, so he became responsible for the attitude control systems. Glenn had experience flying many types of aircraft, so he oversaw the cockpit layout. Schirra drew responsibility for the life support systems and the pressure suits. Drawing on his experience as a Naval officer, Shepard looked after the tracking network and liaised with the Navy on recovery operations. Cooper and Slayton were Air Force officers with engineering backgrounds, so they dealt with the Redstone Arsenal and Convair, who built the Redstone and Atlas boosters used by Project Mercury. The astronauts affected the design of the Mercury spacecraft in significant ways, insisting that a window be installed, and pressing for a greater degree of astronaut autonomy in flying the spacecraft. The astronauts remained on active duty as military officers, and were paid according to their rank. To supplement their travel, they were provided a $9 per diem () for day trips, and a $12 per diem () for overnight trips, which did not cover the cost of hotels and restaurant meals. As a result, astronauts avoided spending money while traveling, as they were personally responsible for costs over their allotted per diem. An important component of their income was monthly flight pay, which ranged from $190 to $245 (equivalent to $ to $ in ). The astronauts traveled to frequent meetings around the country on commercial flights, which forced them to earn their flight pay on weekends. Grissom and Slayton regularly drove to Langley Air Force Base, and attempted to fly the required four hours a month, but had to compete for T-33 aircraft with colonels and generals. Cooper traveled to McGhee Tyson Air National Guard Base in Tennessee, where a friend let him fly higher-performance F-104B jets. This came up when Cooper had lunch with William Hines, a reporter for The Washington Star, and was duly reported in the paper. Cooper then discussed the issue with Congressman James G. Fulton. The matter was taken up by the House Committee on Science and Astronautics. Within weeks the astronauts were given priority access to USAF T-33s, F-102s and F-106s at Langley. In 1962, NASA acquired a fleet of T-38s for their use. After General Motors executive