LIVE STREAM tonight, 10 pm ET / 7 pm PT 1/25/18 at https://www.youtube.com/nasajpl/live.
by Pete Russell, 1/25/18
January 31, 1958. A new house cost about $12,750, Old Yeller was popular in theaters, and radios blared At the Hop, Great Balls of Fire and Peggy Sue.
In Cape Canaveral, FL, the countdown began. At 10:48 pm they hollered “lift-off,” and the US was officially in space. Atop a Jupiter-C rocket sat Explorer 1. Explorer 1 was the first successful U.S. satellite, a 30-pound science instrument that would spend 12 years in space.
Next week marks 60 years since that launch, and NASA is celebrating the anniversary with a series of commemorative events. There’s a big kickoff happening tonight, Thursday, Jan. 25, 2018. It’s available streaming live at https://www.youtube.com/nasajpl/live.
The Jupiter-C Rocket
Developed under the direction of the legendary Werner von Braun, the Jupiter-C was based on the Redstone intermediate range ballistic missile (IRBM) design. Originally intended to carry a nuclear warhead, variations on this rocket thankfully found extensive use in space exploration. A later version, the Mercury Redstone, would put the first American astronauts in space.
The Jupiter-C was also known as the Juno-I. The Jupiter-C is a four-stage propulsion system weighing about 64,000 pounds when fully fueled.
The first stage is the primary booster, which comprises the majority of the weight and size of the complete system. It’s about 47 feet high, roughly the height of a five story building. This primary booster is a liquid fuel rocket that burns liquid oxygen mixed with a secondary liquid compound. The rocket produces 83,000 pounds of thrust, providing nearly 20,000 pounds of thrust more than it weighs.
The second, third and fourth stages are comprised of clusters of small solid fuel rockets. They all use the same propulsion engine, a scaled down version of the Sergeant rocket. The second stage contains a cluster of 11 rockets, the third stage contains a cluster of three rockets, and the fourth stage contains a single rocket and weighs only 80 pounds.
The Explorer 1 Capsule
The cigar-shaped capsule was built at the Jet Propulsion Laboratory in Pasadena, California, in the years before the JPL joined NASA. At the time of Explorer ones construction, the JPL was a US Army facility in joint operation with Caltech. JPL would be shifted under the NASA umbrella in December 1958.
Explorer 1 would later be called “a watershed moment for the nation that also defined who we are at JPL” by Michael Watkins, current director of JPL.
The Explorer 1 capsule was officially known as Satellite 1958 Alpha. Including the stage four booster, the assembly was about 80 inches long, nearly 7 feet. Not factoring in the weight of the rocket booster, the Explorer 1 just over 30 pounds. A little over 18 pounds of that was instrumentation, including batteries.
The instrumentation section contained a cosmic-ray detection package, an internal temperature sensor, three external temperature sensors, a nose-cone temperature sensor, a micrometeorite impact microphone, and a ring of micrometeorite erosion gauges. Six antennas and two 60 milliwatt transmitters sent data from these instruments to receivers on the ground. By contrast, the transmitter of a typical cell phone these days puts out perhaps 1,000-2,000 milliwatts.
Orbit, Service Life and Discoveries
Explorer 1 settled into an elliptical orbit. Its closest approach to earth was about 225 miles, its farthest reach about 1,595 miles. The satellite completed an orbit every 114 minutes.
The satellites batteries were mercury-oxide zinc formulation, an early battery type that’s now banned due to toxic disposal concerns. The formulation is known for long life and steady output voltage. The batteries in Explorer 1 lasted almost 4 months, finally dying on May 23, 1958.
About 90 minutes after launch, JPL stations in California received the first transmissions from Explorer 1.
The key finding of the mission was existence of “Van Allen Belts,” which are areas of charged particle radiation trapped by the Earth’s magnetic field. The belts are named after James Van Allen, who designed and built scientific instruments housed in the Explorer 1 instrumentation section.
End of Mission and Legacy
After its batteries died in 1958, the Explorer 1 capsule continued in orbit for another 12 years. March 31, 1970, the satellite entered the upper edge of Earth’s atmosphere. That caused the Explorer 1 to rapidly slow down, plunge toward Earth and burn up in the atmosphere.
In the intervening 60 year span, the Explorer 1 has been largely forgotten as NASA has continued to achieve milestone after milestone in space exploration. Its significance, though, cannot be underestimated. It set a high bar as not only the first successful US orbiter, but as a flagship science mission. In NASA’s initial success launching an orbiting craft, it discovered something vital about the Earth we live on.
All the NASA missions that have followed Explorer 1 honor the scientific discovery, success and legacy of this landmark mission. AS NASA begins its celebrations of this 60-year anniversary, the long-forgotten Explorer 1 mission once again returns to public attention. Congratulations, old friend, for launching a proud history of exploration, science, and an age of wonder.