Sputnik: 50 Years Later

Sept. 20, 2007 -- When the former Soviet Union launched the world's first satellite into orbit 50 years ago, most people in the United States were filled with shock and dread that their Cold War foe would soon follow up with nuclear-tipped missiles.

But members of the science community were distracted by a more immediate situation: trying to figure out why the little spacecraft's beep varied as it periodically flew overhead.

With its 1 watt of power, Sputnik, which means "companion" in Russian, transmitted radio signals for three weeks after reaching space on Oct. 4, 1957.

While schoolchildren practiced bomb drills, scientists and amateur radio operators studied the signals, which changed as they passed through different parts of Earth's outer atmosphere, the ionosphere, which contains particles ionized by solar radiation.

The early insights into Earth's ionosphere were quickly eclipsed by the discovery of radiation belts surrounding the planet, credited to astrophysicist James Van Allen. The discovery was made by the first U.S. satellite in orbit, Explorer 1.

Though it flew less than four months after Sputnik, the Soviets had already launched its second satellite, Sputnik 2, which held the first living being into space, a dog named Laika.

Today, robotic space probes have visited, or are en route to, every planet in the solar system as well as a few asteroids and other destinations. The earliest satellites have left the solar system entirely and are entering interstellar space.

Closer to home, a space station is under construction, spearheaded by the United States and Russia, which have been sharing living quarters and work in orbit for more than a decade.