NASA: Explorer 1 The First US Explorer

An exploded view of the first successful U.S. satellite launched in 1958, Explorer I. Credit: NASA/Marshall Space Flight Center Collection.

On September 29, 2011, NASA announced the short list for five potential new "Explorer class" spacecraft.

These missions are by definition small and relatively inexpensive, designed to be led by a small team.

The Explorer class missions are numbered at 92 so far, with more constantly planned. Explorer class spacecraft recorded the signature left over from the big bang.

They mapped out the complex geometry of Earth's magnetic environment. They found gamma rays coming from everywhere in the sky. They help warn scientists of incoming radiation from solar flares.

"The neat thing about the Explorers is that they're tailored to a specific problem," says Wilt Sanders the program scientist for the Explorer's Program.

"That's their strength. They're relatively inexpensive but they've come up with game changing results."

And it all began over five decades ago.

The First Explorer
It was January 31, 1958 and a Juno 1 rocket was almost ready to launch. It carried precious cargo - a satellite called Explorer 1, that everyone hoped would be the first U.S. satellite in space.

The mood among those at Cape Canaveral Air Force Station, Fla. was tense. Not only had the Soviets already successfully launched Sputnik into space, but three months earlier, a rocket attempting to launch a U.S. satellite had flown a mere four feet before tumbling back to the ground.

The familiar countdown began: "10 . . . 9 . . . 8 . . . " and at 10:48 p.m. EDT, the Juno shot up, climbed over 200 miles into the sky, and released Explorer 1 into space.

It wasn't until some two hours later, when the satellite had made its first complete orbit of Earth and was in close enough range to send a signal that it was operational, that the observers rejoiced. The very first U.S. satellite was officially a success.

For many, the tale of Explorer 1 stops here, a triumph of human ingenuity in reaching space. But, truly, that's only the beginning of the story. "Explorer 1 was also a science mission," says Willis Jenkins, the program executive for NASA's Explorer program.

"This wasn't just launched to get a satellite up in space, it was meant to bring science data back."

And it certainly did. Explorer 1 contained experiments that turned our understanding of space upside down.

To this day, scientists try to understand the dynamic, seething environment encircling Earth - known as the Van Allen radiation belts - that Explorer 1 helped discover.