With the startling power of its twin rotors and its 200-horsepower engine behind my shoulder blades screaming like an army of leaf blowers, it felt almost as if I were doing the lifting myself, with muscles I did not know I had. It felt like living in the future  and, even better, the future we imagined back when it was something to be hoped for rather than feared.

Pressing the left-hand stick forward caused the device to pitch forward slightly, and the jetpack began advancing, a few feet above the lawn. Mr. Martin and a colleague steadied it by grasping hand rails and trotting alongside, like parents teaching a child to ride a bicycle without training wheels.

Then, coming around a curve, Mr. Martin jogged to the right to avoid some equipment on the ground, bringing the jetpack too close to an overhanging tree. The limb was sucked into the rotors with a brief but sickening sound, like a blender trying to make a margarita with twigs. Luckily, he had spare parts and access to a workshop to replace a chipped rotor.

Mr. Martin started trying to make his jetpack dreams come true in college. While he was studying biochemistry, he was also working on painstaking calculations of thrust in the library and researching the Wright brothers’ methodical approach to technology development. He later had jobs in the pharmaceutical and biotechnology industries, but much of the money went to the work going on in his garage. He built a network of enthusiasts who helped him develop his ideas.

In June 1997, seven weeks after the birth of his second child, Mr. Martin figured his prototype was now powerful enough to lift its first flier, so long as that person weighed less than 130 pounds. So he turned to his wife. “I said, ‘Hey, Vanessa, what are you doing tonight?’ ”