Highest altitude balloon flight (FAI approved)

The highest-altitude balloon flight recognized by the FAI was undertaken on 4 May 1961 by the US Navy's Strato-Lab V balloon. The crew of Malcolm Ross and Victor Prather (both USA) flew the 280,000 m3 (10 million cu ft), helium-filled polyethylene balloon and its open-frame gondola to an altitude of 34,668 m (113,740 ft). Strato Lab V lifted off from the deck of the USS <em>Antietam</em>, and landed in the Gulf of Mexico 9 hours 54 minutes later.

The FAI's rules for flight records require that the crew take off and land safely with their aircraft. This means that, for example, the flights of the X-15 rocket plane (which was carried to the stratosphere by a mothership) aren't accepted, nor are the high altitude balloon flights of Joe Kittinger, Felix Baumgartner and Alan Eustace (all of whom parachuted back down to Earth). This remains the highest balloon flight in which the crew remained in control of their aircraft for the full duration of the flight.

The purpose of this mission, officially called Strato Lab V High, was primarily to test the new B.F. Goodrich Mark IV pressure suit by exposing it to near-vacuum conditions for a long period of time. The suit had been chosen as the basis for the Project Mercury space suit, and so it was important to test its capabilities ahead of the first US crewed spaceflights.

The crew consisted of Lieutenant Commander Malcolm Ross, a US Navy test pilot who was a veteran of eight previous high altitude balloon flights, and Lt Cmdr Victor Prather, a flight surgeon involved in the development and testing of pressure suits.

Though long and exhausting, the flight was a complete success. The suits performed perfectly, and allowed Ross and Prather the flexibility needed to carry out the various experiments on their schedule.

Originally, the plan was for the balloon to land back on the deck of the <em>Antietam</em>, which would follow their progress across the Gulf of Mexico. As this would be a difficult manoeuvre to pull off, however, the personnel involved had done some training in water-landings and recovery.

What actually happened would serve as a sobering lesson for the mission planners at NASA, who were intending to use a similar water-landing and recovery profile for the Mercury program. After the balloon splashed down, a helicopter lowered a harness down to the floating gondola. Ross was safely winched up and carried back to the ship, but Prather – tired and encumbered with a bulky pressure suit – slipped and fell into the water. He drowned before Navy swimmers could reach him.