On Wednesday evening, 31 January, a full 60 years passed since a Juno I booster roared into the night from Launch Complex (LC)-26A at Cape Canaveral to deliver America’s first successful artificial satellite into orbit. Today, many features of this historic location—including the blockhouse, control consoles and a great deal of legacy equipment—remain in place and the site is now the home of the Air Force Space and Missile Museum. Yet what happened here, six decades ago, would begin the first of a long-standing series of U.S. records in space. Explorer 1, which went on the discover the Earth-girdling Van Allen radiation belts, was the first mission to enter Medium Earth Orbit (MEO) and although it remained operational for just 16 weeks, the satellite itself would endure for a dozen years, finally burning up in the atmosphere in March 1970.
Video Credit: NASA History
In the uncertain times after the close of World War II, efforts by both the United States and the Soviet Union to achieve military supremacy over the other had progressed from nuclear weapons to hydrogen bombs to Intercontinental Ballistic Missiles (ICBMs), the first of which—Sergei Korolev’s R-7—launched in August 1957. By this stage, both superpowers had publicly announced their intent to launch artificial “Earth satellites” for scientific research during the 18-month-long International Geophysical Year (IGY), which extended from July 1957 through December 1958. To much surprise and dismay in the West, it was the Soviets who first reached Earth orbit with Sputnik 1 in October 1957 and they kept up the pace by launching a dog, Laika, aboard Sputnik 2, a month later.
The United States’ inaugural attempt to gets its own satellite into space went dreadfully awry on the morning of 6 December, when the U.S. Navy’s Vanguard booster rose just four feet (1.2 meters) from LC-18A at the Cape, before exploding in a conflagration. Aboard, the tiny Vanguard 1A satellite was thrown clear of the destruction and landed nearby, its radio transmitter still beeping. Eight weeks later, at LC-26A, a Juno I booster was readied for its own launch, carrying Explorer 1. A member of the Army’s Redstone family, the Juno I was based upon the earlier Jupiter-C sounding rocket, which had flown three times in 1956-57 to evaluate the nosecone re-entry characteristics.
Standing 70 feet (21.2 meters) tall, the Juno I was a four-stage beast. At the instant of liftoff, the single Rocketdyne-built A-7 engine of its Redstone core burned liquid oxygen and a substance called “hydyne”—a 60-percent mix of unsymmetrical dimethyl hydrazine and 40-percent diethylenetriamine—to generate 93,564 pounds (42,439 kg) of thrust. Launch was originally scheduled for 28 January 1958, but was scrubbed due to unusual weather in the lower stratosphere. In those final days of the month, the jetstream was far further south than normal and concern existed that the Juno I could be lost if it launched in such dynamic conditions. An attempt on the 30th was considered ill-advised and launch was rescheduled for the following evening. As darkness fell over Florida on 31 January, everyone willed Explorer 1 to succeed and make the United States a spacefaring nation.
With the trusty A-7 powering it on its way, the Juno I roared away from LC-26A at 10:48:16 p.m. EST, turning night into day for miles across the marshy Florida landscape. The first stage burned for over 2.5 minutes, before it was jettisoned via a system of explosive bolts, clearing the way for the rocket’s solid-fueled second and third stages to pick up the baton to deliver America’s baby satellite into orbit. These two stages were both integrated within a “tub”, atop the Redstone core, which had been “spun-up” before launch for the purposes of balance and stability. Its spinning motion was easily visible in the launch imagery from daytime Juno I launches, later in 1958.
Following the burnout of the first stage, the remainder of the stack “coasted” for several minutes, before it reached the apex of its vertical flight and second-stage ignition was commanded by radio signal from the ground. The second stage consisted of 11 Sergeant motors, arranged in a circular configuration, which produced a total yield of 16,500 pounds (7,840 kg), whilst the third stage sat in the center, generarting 4,500 pouunds (2,040 kg) from its trio of Sergeant motors. Both stages fired for about 6.5 seconds apiece, before separating. The final stage, the fourth, was a single Sergeant, which sat atop the tub and burned with 1,500 pounds (680 kg) of thrust for a further 6.5 seconds to insert Explorer 1 into orbit. It remained physically attached to the satellite.
By the time the fourth stage burned out, Explorer 1 was traveling at an orbital velocity of some 18,000 mph (28,900 km/h). Agonizingly, the tracking station in Goldstone, Calif., was not able to report conclusively on the success of orbital injection until 90 minutes after launch, since the orbital radius was larger than anticipated. Not until 1:30 a.m. EST on 1 February 1958 was the news announced via press conference in the Great Hall at the National Academy of Sciences in Washington, D.C.
America’s first successful artificial satellite entered a highly elliptical path around the globe, with a perigee of 224 miles (360.4 km) and an apogee of 1,575 miles (2,534.7 km). Circling Earth every 114.9 minutes, the 30.6-pound (13.8 kg) satellite was far smaller and lighter than its Russian Sputnik predecessors, yet it boasted a far more sophisticated payload of instrumentation. And that instrumentation would very shortly begin to bear fruit.
Today, Explorer 1’s main claim to scientific fame is that it discovered the Van Allen radiation belts, girdling Earth and extending from an altitude of 300 miles (500 km) to around 36,000 miles (58,000 km) above the surface. From time to time, its data would report expected cosmic ray levels (about 30 counts per second), followed by a strange zero counts. Dr. James van Allen of the University of Iowa, who designed Explorer 1’s scientific payload, realized that the zero counts occurred at an altitudes over 1,200 miles (2,000 km), whilst passes at 300 miles (500 km) showed predicted values. Subsequent observations revealed that the satellite’s Geiger counter had been saturated by strong radiation from hitherto-unknown belts of charged particles.
Later named in van Allen’s honor, these take the form of energetic particles, many of which originate from the million-mile-per-hour (1.6 million km/h) solar wind. The belts are anchored around Earth by our planet’s intrinsic magnetic field. In addition to its omni-directional Geiger counter, Explorer 1 was equipped with temperature sensors and acoustic and wire-grid detectors to observe micrometeoroid impacts. Thanks to its on-board nickel-cadmium batteries, it maintained operations until 23 May 1958, but its high orbit kept it aloft for a dozen years, before it re-entered the atmosphere to destruction on 31 March 1970.
Yet the “Explorer” program name endured far beyond its humble first incumbent. Over the next five decades, over 90 missions of scientific exploration would be assigned Explorer designations, with objectives running the gamut from radiation and energetic particles studies to magnetospheric research and gamma ray astrophysics to atmospheric observations. Others would conduct radio, infrared, ultraviolet and X-ray astronomy.
Significant members of the fleet would include the Cosmic Background Explorer (COBE), the Extreme Ultraviolet Explorer (EUVE) and the Wilkinson Microwave Anisotropy Probe (WMAP). In the coming months, the next two members of the Explorer program—the Ionospheric Connection Explorer (ICON) and the Transiting Exoplanet Survey Satellite (TESS)—will be launched, via the Pegasus-XL and Upgraded Falcon 9 boosters, respectively. They will continue a long-running legacy as Explorer enters its seventh decade of operations.