A TR-1A (U-2) spy plane at the Grand Forks Air Force Base (GFAFB) 'Friends And Neighbors Day' on May 27th 1989.
Because of the high operating altitude (70,000 feet) and the cockpit's partial pressurization, equivalent to 28,000 feet pressure altitude, the pilot wears a partially pressurized space suit, which delivers the pilot's oxygen supply and provides emergency protection in case cabin pressure is lost. While pilots can drink water and eat various liquid foods in squeezable containers through a self-sealing hole in the face mask, they typically lose up to six pounds of weight on an eight-hour mission. To decrease the chance of developing decompression sickness, pilots breathe 100% oxygen an hour prior to take off to remove nitrogen from the body. A portable oxygen supply is used prior to entering the aircraft. (Wikipedia)