Clifton M. “Demi” McClure was born on November 8, 1932, in Anderson, South Carolina. A graduate of Anderson High School, he received a Bachelor of Science degree in Materials Engineering and in 1954 and a Master of Science degree in Ceramic Engineering from Clemson University. Upon graduation, he was commissioned as a lieutenant in the United States Air Force.
After flight training, Lieutenant McClure served as a T-33 instructor pilot at Laughlin Air Force Base (AFB), Del Rio, Texas, and Bryan AFB, Bryan, Texas. Afterwards, he worked on the Solar Furnace Project at Holloman AFB, New Mexico. In 1958, while still assigned to Holloman, McClure piloted the Manhigh III balloon, the final Manhigh mission, to 98,000 feet above the Tularosa Basin. Project Manhigh was established in December 1955 to obtain scientific data on the behavior of a balloon in an environment above 99% of the earth’s atmosphere and to investigate cosmic rays and their effects on humans.
The project consisted of a series of flights in high-altitude Winzen helium balloons, which tested man’s ability to live and work for long periods of time in a sealed-cabin environment. Project Manhigh was a precursor to the Mercury flights of America’s first manned space program.
Three balloon flights to the edge of space were made during the program: Manhigh I reached an altitude of 18.5 miles, with Captain Joseph Kittinger on June 2, 1957; Manhigh II flew to 19.2 miles, piloted by Major David Simons on August 19 and 20, 1957; and Manhigh III ascended to 18.6 miles, piloted by Lieutenant Clifton McClure on October 8, 1958.
Including the pilot and scientific equipment carried aboard, the total weight of the Manhigh gondola was 1640 pounds. At maximum altitude, the balloon expanded to a diameter of 196 feet with a volume in excess of 85,000 cubic meters.
The purpose of Manhigh III was to make scientific observations through the eyes of the pilot in contact with experts on the ground. Medically, it studied the ability of the pilot to make these observations and developed and tested techniques to assess his performance during the flight to and descent from an altitude of around 100,000 feet. Lieutenant Clifton McClure, aboard the Manhigh III balloon, reached 98,000 feet above the Tularosa Basin of southern New Mexico.
The cramped capsule, three feet in diameter and nine feet high, was crammed with batteries, cameras, a radio, and medical equipment to monitor his heartbeat and temperature. From a porthole, McClure could see the changing colors of the mountains and desert below as the balloon lifted him higher into the sky.
Manhigh III began to descend as planned but trouble followed. The other flights had ice caps in the capsules to control heat, but the third flight didn’t. Lower temperatures early that morning caused attendants to decide one wasn’t necessary. However, McClure began having serious heat problems on the way up and his body temperature rose to 108.6 degrees by the time the balloon began to descend. He drank water and juice during the agonizingly slow descent, performing his duties ”as slowly as I could to conserve energy and keep from passing out.” He finally landed in the desert at 7 p.m., releasing the parachute and breathing a great sigh of relief when the capsule stayed upright and didn’t topple over, perhaps spilling battery acid on him.
During his twelve-hour flight, McClure endured 137 percent more heat than it was thought the human body could tolerate while at the same time performing well enough to record ideas for improving the next flight. David Simmons, who was the flight surgeon for McClure’s flight, and had flown Manhigh II, summed up what McClure taught them about human spaceflight: “An essential quality necessary to an astronaut would be stamina; not in a purely physical sense but in a psychophysiological sense: a combination of deep physical reserves plus the all-important emotional determination to use those reserves.”
Despite McClure’s performance, his application to become an astronaut was turned down by NASA “because he was too tall” (maximum height restrictions were necessary due to the cramped conditions in the Mercury capsule). In September 1960, Lieutenant Clifton McClure was awarded the Distinguished Flying Cross for the Manhigh III mission. After his retirement from the Air Force, he became an engineer and often worked with NASA. Clifton “Demi” McClure died on January 14, 2000, at his home in Huntsville, Alabama.