Spaceflight Insider

Our SpaceFlight Heritage: Explorer 1 and the birth of the U.S. Space Program

Explorer 1 Werner von Braun Pickering James Van Allen NASA photo posted on SpaceFlight Insdier

Explorer 1 was the first satellite launched by the United States on Jan. 31, 1958. Photo Credit: NASA

CAPE CANAVERAL, Fla. — Today, the world takes satellite launches for granted. With two (or more) taking place during any given month. Fifty-eight years ago on this date in space flight history, however, there had only been two satellites sent into orbit – and they were both from the Soviet Union. Sputnik 1 on October 4, 1957, and Sputnik 2 on Nov. 3, 1957. The U.S. was under pressure to match these feats – something that it would try to do with Explorer 1.

Launch of Explorer 1 from Cape Canaveral Air Force Station NASA image posted on SpaceFlight Insider

Explorer 1 was launched on January 31, 1958, at 10:48 Eastern Time (Feb. 1, 1958, 03:48 GMT). Image Credit: NASA

The U.S. Army Ballistic Missile Agency, along with Werner von Braun, had been directed to launch a Jupiter-C booster with the Explorer 1 satellite. They would do so on Jan. 31, 1958. While about three-and-a-half months after the Soviet Union lofted Sputnik 1, it trumped the Soviets in terms of scientific discovery. Liftoff took place at 10:48 Eastern Time (Feb. 1, 1958, 03:48 GMT) from Cape Canaveral Air Force Station’s (known as the Cape Canaveral Missile Annex at that time) Launch Complex 26.

As mentioned, while the Russians might have assured their place in the history books, the Americans carried out a more substantive mission, one which achieved actual science (Explorer 1 was the spacecraft that discovered the radiation belts that surround Earth – which would be named after Dr. James Van Allen – the scientist in charge of Explorer 1′s science experiment).

Explorer 1 was designed and built by an organization that would go on to be legendary – NASA’s Jet Propulsion Laboratory. It accomplished this is less than three months – and it would operate the satellite once it was delivered to orbit.

As noted, Explorer 1 employed a scientific instrument, the cosmic ray detector. Used to gauge the radiation environment above our home world, it discovered lower amounts of radiation than had been anticipated.

Van Allen, from the University of Iowa, thought that the device may have become saturated with radiation.

The Van Allen Belts, like all scientific discoveries, had to be validated. A second U.S. spacecraft, which was launched two months after Explorer 1, confirmed the existence of the Van Allen Belts.

The U.S.’s first satellite orbited Earth at a perigee of some 220 miles (354 kilometers) and an apogee of  1,563 miles (2,515 kilometers). According to NASA, it orbited our planet about once every 114.8 minutes – or a total of 12-and-a-half orbits every day.

The satellite was about 80 inches (203 centimeters) in length and 6 inches (16 centimeters) in diameter and weighed about 31 lbs (14 kilograms). Explorer 1′s last transmission took place on May 23, 1958. It would continue orbiting Earth until March 31, 1970 – when it re-entered and burned up in Earth’s atmosphere.

Explorer 1 was rushed to orbit after the failed Vanguard 1 mission. However, the follow-on mission to Explorer 1 – Explorer 2 – was also a failure (due to the fourth stage of the Jupiter-C rocket it was riding failing to ignite). Explorer 2 was launched on March 5, 1958. The U.S. got back into the space race just three weeks later with the launch of Explorer 3 (which was operational until June 16, 1958).

Explorers 4 and 5 were also launched in 1958, with #4 operating until Oct. 6, 1958, and #5 ending in failure. In terms of the U.S. Space Program, 1958 would prove to be a pivotal year.

On July 29, 1958, NASA was formed and would go on to include the Jet Propulsion Laboratory as part of its organization. The success of Explorer 1 would be built upon as NASA would go on to carry out ever-more complex and, eventually, crewed missions. The Explorer flights would serve as the classroom where NASA learned how to conduct successful launches into the black – and where they learned that space flight is never routine.

Video courtesy of NASA / Mark Gray – Spacecraft Films


Jason Rhian spent several years honing his skills with internships at NASA, the National Space Society and other organizations. He has provided content for outlets such as: Aviation Week & Space Technology,, The Mars Society and Universe Today.

Reader Comments

The fact that ABMA/JPL had successfully test fired the Jupiter-C in its satellite launch vehicle configuration on September 20, 1956 but was prevented by the Eisenhower Administration from an actual satellite launch frustrated Wernher von Braun to no end.

The US could have attempted to orbit a satellite up to a year before the launch of Sputnik. The history of the Space Age would have surely unfolded very differently if Explorer had been first.

Great post – thank you!

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