By Dr. Gary L. Deel, Ph.D., J.D.
Faculty Director, School of Business, American Military University
The third and final article in a three-part series on the earliest satellites launched by the Soviet Union and the United States.
In the first two parts, we discussed Sputnik I, the first satellite ever put into orbit, and Sputnik II, the follow-on mission to Sputnik I. In this last part, we’ll examine Explorer I, the first U.S. satellite in space.
Designed by Caltech’s Jet Propulsion Lab, NASA’s Explorer I satellite was launched on January 1, 1958, by a Juno I booster rocket from Cape Canaveral, Florida. Juno I was actually a Jupiter-C ballistic missile rocket that had been modified by the U.S. Army and NASA to accommodate the satellite payload.
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The most prominent mission of Explorer I was to prove that the United States was just as capable of launching orbiting satellites as the Soviet Union. Ancillary mission objectives included collecting data on cosmic rays and micrometeorite impacts.
By comparison to the Sputnik I and II, Explorer I was much smaller. NASA’s satellite weighed only about 31 lbs. Explorer I had a rocket shape although it was only about 6.5 feet long and six inches in diameter. The main hull was actually a hollowed fourth stage casing from a Sergeant short-range, surface-to-surface missile.
Three striking features of the spacecraft were:
- The booster cone at the bottom of the actual Explorer I body
- The four whip-like antennas that protruded from the main fuselage about halfway between the nose and the base
- The fiberglass slot antennas at the hull joints.
The communication system of Explorer I consisted of two radio transmitters. One was connected to the fiberglass slot antennae in the body, which operated at 108.03 MHz; the other was connected to the four whip-like antennas, which operated at 108.00 MHz.
Explorer I Was Designed to Spin in Orbit to Stabilize its Attitude and Keep its Antennas Fully Extended
The satellite was designed to spin in its orbit in order to stabilize its attitude and keep the whip-like antennas fully extended. But ultimately this didn’t work due to flawed understandings at the time of kinetic rotational energy and rigid body dynamics. Explorer I was powered by nickel-cadmium batteries that comprised approximately 40 percent of the total payload of the spacecraft.
Other than the batteries, radio transmitters, and antennas, the scientific payload of Explorer I consisted of a cosmic ray detector, five temperature sensors, and an acoustic sensor and wire grid detector for identifying micrometeorite impacts.
There was no apparent ground control of Explorer I. Because it lacked any attitude control system, ground controllers could not make any changes once the spacecraft was launched.
Explorer I used a “passive” thermal control system to regulate its operating temperature. This consisted of alternating white and dark green stripes on the outside of the hull which kept internal temperatures at acceptable levels. This system worked well and allowed the onboard instruments and electronics to function for as long as the batteries supported them.
Explorer I Remained in Orbit Far Longer than its Russian Counterparts
Explorer I’s batteries died after about four months in orbit, far exceeding the active lifespans of Sputnik I and II, which each lasted only a few days. Explorer I also remained in orbit far longer than its Russian counterparts; it orbited Earth more than 58,000 times over 12 years before burning up in the atmosphere in 1970. The only limitation to the useful life of Explorer I was the lifespan of its batteries. If it had had a more robust power supply, there is no reason to think that Explorer I could not have continued its mission.
Explorer I was launched into orbit with a perigee of 222 miles and an apogee of 1,580 miles. This altitude — significantly higher than those of the Sputnik launches — was primarily responsible for the longer flight duration. The orbital period for Explorer I was about 115 minutes, and the inclination was 33 degrees.
Explorer I was an overall success. The primary objective of the mission from a geopolitical perspective was to demonstrate that the United States was competent to launch orbiting satellites and compete with the Soviets. Explorer I achieved that goal. It also returned useful information on micrometeorite impacts. Finally, although not confirmed until the Explorer III mission, the cosmic ray data collected by Explorer I constituted the original discovery of the Van Allen radiation belts.
The earliest satellites from Roscosmos and NASA were impressive innovations for their time. Their flights tested and refined the fundamental systems that are still an evolving part of modern spacecraft today. The two countries learned much from each other’s achievements, and today the two space agencies partner in peaceful collaboration on spacecraft development and space exploration missions.
In fact, next Wednesday, May 27, at 4:33 p.m. ET, “a new era of human spaceflight is set to begin as American astronauts once again launch on an American rocket from American soil to the International Space Station.”
It will be the first orbital human spaceflight to launch from U.S. soil since NASA’s space shuttle fleet retired in July 2011. Since then, NASA has relied solely on Russia’s Soyuz spacecraft to perform this taxi service.
There is no doubt that the spacecraft of tomorrow will scarcely resemble the wildest musings of our imaginations. However, the newest iterations of satellites and spacecraft will still owe a debt of gratitude to the very first versions of their kind, which paved the way for everything that has followed since.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a J.D. in Law and a Ph.D. in Hospitality/Business Management. Gary teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.