DOS PALOS, Calif. — Only half-filled with helium, and already more than 12 feet wide, the giant plastic envelope shimmered and shook in the breeze like some airborne jellyfish rising through a gentle current.

Soon it shot into the sky, soaring thousands of feet with a payload of sophisticated radio gear, processors and solar panels. Its launch Friday was part an offbeat experiment by Google in using lighter-than-air balloons, a concept pioneered in the 18th century, to solve the 21st-century problem of delivering Internet service to underserved parts of the world.

“This is a great, big, hard problem,” said Richard DeVaul, a Google engineer and chief technical architect for the company’s Project Loon, so named in part because even Google concedes the idea sounds a little crazy.

But after a trial run in New Zealand earlier this year, DeVaul and other engineers on the project say they believe a global network of low-cost, high-altitude balloons could carry enough wireless transponders to beam Internet connections to remote parts of Africa, Asia and other developing regions.

They’re now embarking on a new series of tests in California’s Central Valley, aimed at working out the answers to a multitude of technical questions that must be resolved to make the project work.

Google invited a reporter and photographer to observe Friday’s launch at a rural airfield that’s primarily used by crop-dusting planes. More tests are planned this summer in the same area.

“Our main challenge right now is power,” said Sameera Ponda, a Massachusetts Institute of Technology-trained aerospace engineer hired by Google to work on the project. She explained that the Loon team needs more data to decide how to configure the solar array and batteries so they can keep a balloon’s radio equipment and computers running for weeks at a time, even at night, at frigid altitudes of 12 miles or more above the Earth.

“Our goal is to provide Internet service to people in areas that can’t afford to throw down fiber lines or even cell towers,” Ponda explained. “We’re hopefully going to be able to make that a reality in the next few years.”

The concept calls for a fleet of hundreds or even thousands of balloons that will float twice as high as most jetliners fly, in a circle around Earth. But while it sounds relatively simple, the logistics are mind-boggling.

Since the balloons drift with the wind, Google engineers devised a system to raise or lower them in order to catch the air currents needed to keep them floating just the right distance from each other — and aligned so if one floats out of range from Internet users in a particular region, another will come along and take its place.

The balloon launched Friday is a test device; its radio equipment was not intended to deliver an Internet connection. It also was filled only with helium and is smaller than those tried in New Zealand, Acosta said. The larger models can be 45 feet in diameter and were designed by Google with separate chambers for helium and air, so the latter can be pumped in or out to raise or lower the balloon.

Controlling the balloons is a massive computational challenge, DeVaul said. Fortunately, he added, “at Google we’ve got a bunch of really clever computer scientists and a lot of computing power. We now believe we can make the rest of this work, technically.”