Tomorrow, January 31, marks 50 years in space for the United States.
50 years ago, on the evening of January 31, 1958, a Juno rocket (also known as a Jupiter-C rocket), which was basically a modified Redstone ballistic missile, roared to life on a launch pad at Cape Canaveral, in Florida. Seconds later, at 10:48 pm Eastern Standard Time, the rocket lifted off. The rocket was the product of the hard work of Wernher von Braun, of the Army Ballistic Missile Agency. The fourth stage of the rocket, though, was built and operated by the Army’s Jet Propulsion Laboratory (later that year, both the ABMA and JPL were transfered to the newly created NASA). Just before the rocket was launched, the third stage was set spinning to stabilize it once it was released from the second stage. This gave the top of the rocket a rather peculiar look, rather like a spinning Coke can sitting on top of the rocket. The fourth stage contained a small solid rocket engine to put it into orbit, making it a satellite. This satellite was about 6 feet 8 inches (203 cm) long and 6.25 inches (15.9 cm) in diameter. It was not quite 14 kilograms in mass (weighing almost 31 pounds). It carried a small instrument package of mass about 4.8 kilograms (a bit under 11 pounds). The instrument package was largely designed by James van Allen of the State University of Iowa (now, just the University of Iowa). Nearly 40% of the satellite’s mass was batteries to provide power for the instruments and transmitters.
The satellite, officially Satellite 1958 Alpha, was dubbed Explorer 1. It was the United States’ first orbiting satellite. There had been previous launches of rockets carrying payloads to the edge of space in suborbital flights, but Explorer 1 was the first thing that America put into orbit. It followed earlier failed attempts to launch Vanguard spacecraft. Both the United States and the Soviet Union had declared intentions of launching an orbiting satellite during the International Geophysical Year, which ran from July of 1957 through December of 1958. The Soviet Union beat America into space by launching Sputnik 1 on October 4, 1957. On November 3, 1957, they surprised the world again by launching a dog into space aboard Sputnik 2. Vanguard was not doing well, and America was falling behind in the space race. So, von Braun was given the go-ahead to complete development on his plans to place a satellite into orbit.
Explorer 1 was launched into an elliptical orbit that ranged from a perigee (the closest to Earth) of 220 miles (358 kilometers) up to an apogee (its farthest from Earth) of 1580 miles (2550 kilometers). It circled the Earth every 114.8 minutes. On board were instruments recording the space environment. Data was broadcast through whip antennae extending from the craft. Once in orbit, the spin stabilization switched unintentionally into a flat spin, with the craft spinning end over end about its center of mass. You can see the launch of Explorer 1 in this Army video on YouTube:
Radiation sensors aboard Explorer 1 detected regions of high radiation surrounding Earth. Further studies showed that these regions were part of regions of highly energetic charged particles trapped in the Earth’s magnetosphere. These regions, which if you could see them would look sort of like oddly shaped donuts surrounding Earth, are called the van Allen Radiation Belts. Explorer 1 continued to operate for about 111 days, until its batteries failed on May 23, 1958. Over time, Explorer 1’s orbit gradually decayed. It finally reentered Earth’s atmosphere over the Pacific Ocean on March 31, 1970, having completed over 58,000 orbits of the Earth.
(Explorer 1 image courtesy NASA, JPL)