Overhead my onion-shaped balloon spread its 200-foot [61-meter] diameter against a black daytime sky. More than 18 1/2 miles [30 kilometers] below lay the cloud-hidden New Mexico desert to which I shortly would parachute.

Sitting in my gondola, which gently twisted with the balloon's slow turnings, I had begun to sweat lightly, though the temperature read 36° [-38° C] below zero Fahrenheit. Sunlight burned in on me under the edge of an aluminized antiglare curtain and through the gondola's open door.

In my earphones crackled the voice of Capt. Marvin Feldstein, one of our project's two doctors, from ground control at Holloman Air Force Base: "Three minutes till jump, Joe."

I was ready to go, for more reasons than one. For