The world’s unexpected reaction to the launching of Sputnik on October 4, 1957 proved to be of immense propaganda value to the Soviet Union (see “Sputnik: The Launch of the Space Age”). People around the world could clearly see for themselves in the night sky this first artificial Earth satellite and the even brighter spent rocket which launched it into orbit challenging the American image of technological preeminence taken for granted by so many. With reaction to the launch of Sputnik (and its implications for national security) bordering on near panic among some in the US, a response to the Soviet challenge was desperately needed.

The launch of Sputnik on October 4, 1957 made headlines across the globe and shocked many Americans.

On October 11, 1957 the Eisenhower administration officially announced that an upcoming test flight of the Naval Research Laboratory’s Vanguard rocket would attempt to orbit a small satellite (see “Vintage Micro: The First Nanosatellite”). But with the scheduled launch date still a couple of months away, the American public was desperate to see a more immediate answer to Sputnik. As it turned out, they would not have to wait too long due to the efforts of a gifted Swiss astronomer working at Caltech named Fritz Zwicky (1898-1974).

Fritz Zwicky in a lighter moment later in life. (Caltech)


Artificial Meteors

Born in 1898 in Varna, Bulgaria where his Swiss father was a prominent industrialist, Fritz Zwicky moved to Switzerland at age six to live with his paternal grandparents and attend school. Zwicky studied mathematics, engineering and physics at the prestigious Swiss Federal Institute of Technology in Zurich and received his doctorate in 1922. In 1925, Zwicky accepted a fellowship from the Rockefeller Foundation he was offered for his graduate work in quantum mechanics and went to teach at the California Institute of Technology (Caltech).

After coming to the US, Zwicky eventually shifted the focus of his career to observational astronomy becoming a staff member at the Mount Wilson Observatory and Palomar Observatory where he specialized in the study of galaxies. Working with German astronomer Walter Baade at Mount Wilson, Zwicky and Baade were the first to realize in 1933 the difference between ordinary nova in our galaxy and the intrinsically much brighter versions observed in some recently recognized “island universes” or galaxies now called supernova – a term Zwicky and Baade invented. Based on his studies of the motions of galaxies, in 1937 Zwicky was the first to determine that there must be unseen dark matter present to keep these clusters from fly apart.

Fritz Zwicky shown at work in 1936 at the Palomar Observatory’s 46-cm Schmidt telescope. (Caltech)

In 1943 during the height of World War II, Fritz Zwicky was asked to head the research department at the then-new Aerojet Engineering Corporation (the forerunner of Aerojet General which is now part of the rocket engine manufacturer, Aerojet Rocketdyne). While continuing his astronomical research, Zwicky worked on the development of new jet engine technology in his new role as industrial consultant. Following the war, Zwicky became part of the American team assembled by the Department of Defense to travel to Europe and evaluate German rocket technology. Upon his return, Zwicky started to work on how V-2 rocket technology could be employed in the study of the upper atmosphere of the Earth.

At this time, observations of meteors could be used to characterize the properties of the upper atmosphere as they flashed out of existence high above the Earth’s surface. Zwicky proposed creating artificial meteors using shaped charges carried to high altitude by a rocket to propel a slug of metal to hypervelocities. Shaped charges of the sort used in early antitank weapons could accelerate such a slug to velocities comparable to the 10 to 15 kilometer per second speed of the explosives’ detonation wave to produce a visible artificial meteor of known mass and composition allowing the characterization of the physical and chemical properties of the upper atmosphere at altitudes of 40 to 110 kilometers.

V-2 Number 17 used for Fritz Zwicky’s first artificial meteor experiment is shown here being prepared for its launch on December 17, 1946. (Peter Alway)

Using his connections through Aerojet and as a member of Science Advisory Board of the US Air Force, in the spring of 1946 Fritz Zwicky proposed using a captured V-2 rocket to loft his payload of shaped charges to create artificial meteors which would be observed using ground-based telescopes. His proposal was approved and the mission was launched on the evening of December 17, 1946 at 10:12 PM MST from the White Sands Proving Ground in New Mexico. While V-2 Number 17 operated as intended reaching a peak altitude of 188 kilometers, the shaped charges failed to detonate as planned at altitudes of 37, 46 and 55 kilometers probably due to a wiring error. Although Zwicky and his team gathered valuable data on the properties of the ascending rocket’s plume and its interaction with the graphite steering vanes used by the V-2 for attitude control, they failed to create artificial meteors for study.


Off into Solar Orbit

Because of this failure and subsequent doubts voiced by some key experts in the field, Zwicky’s follow on requests to refly his experiment were not approved. Undeterred, Zwicky and his team continued their work to improve their hardware and techniques as well as prove that shaped charges could be used to create observable artificial meteors. Ground tests performed in 1947 at the US Navy’s facility at China Lake, California demonstrated that shaped charges could create hypervelocity projectiles bright enough to be observed from ranges of hundreds of kilometers using the portable Palomar 20-centimeter Schmidt telescope. During subsequent years, Zwicky and his associates at Aerojet continued work with shaped charges and developing new explosives. Encouraged by this work, the US Navy sponsored a series of successful tests using high altitude balloons in 1955.

Cutaway diagram showing the major components of the Aerobee sounding rocket. Click on image to enlarge. (NASM)

With these successes in hand, approval was given to fly an updated artificial meteor experiment on an Aerobee sounding rocket when space became available. The Aerobee was a two-stage sounding rocket originally developed for the US Navy by Aerojet under the guidance of the Applied Physics Laboratory at Johns Hopkins University. Later, upgraded versions were designed and built for the US Navy, USAF and eventually NASA. The first stage consisted of a solid rocket motor which boosted the rocket and its payload to high speeds so that its fins could stabilize the rocket by the time it left its launch tower. The liquid fueled second stage, originally based on work done by Caltech’s Jet Propulsion Laboratory for the WAC Corporal missile, would provide the bulk of the energy to hurl its payload to the edge of space. Although the typical Aerobee payload of a few tens of kilograms was much smaller than that of the V-2 (which was really too large for most early experiments), this purpose-built sounding rocket was much less expensive, easier to launch and more flexible than its larger cousin.

In the summer of 1957, Fritz Zwicky and his collaborators finally got word that they could refly the artificial meteor experiment as part of an Aerobee launch already scheduled for mid-October. Sponsored by the Geophysics Research Directorate of the Air Force Cambridge Research Center, the payload contained three separate shaped charge packages using a common detonator and arranged so that their firing would not interfere with each other. One of the packages was supplied by a group headed by Dr. Thomas Poulter of Stanford University and consisted of an almost cylindrical aluminum plug designed to maximize its velocity. A second package with a larger one-centimeter aluminum plug supplied by a group headed by Dr. John S. Rinehart of the Smithsonian Astrophysical Observatory would travel at a slower velocity. The third package was fabricated by Zwicky’s team and consisted of a 1.5 millimeter aluminum cone propelled by C3 explosives supplied by the USAF.

A view of the three packages of shaped charges mounted on the Aerobee rocket prior to launch. (Caltech)

At 10:05 PM MST on October 16, 1957, the Aerobee rocket carrying the artificial meteor experiment lifted off from Holloman Air Force Base in New Mexico. After 45 seconds, the second stage of the Aerobee had exhausted its propellant and continued its climb out of the atmosphere. Ten seconds later, the artificial meteor payload was separated at an altitude of 56 kilometers leaving the other payload still attached to the rocket to perform its separate mission. After coasting for another 36 seconds, the shape charges were detonated at an altitude of about 85 kilometers. The resulting flash was easily observed from not only the cameras and telescopes deployed in the region, where it appeared as bright as -10 magnitude, but also using the 46-centimeter and 1.2-meter Schmidt telescopes at the Palomar Observatory 1,000 kilometers away where it appeared as a -5 to -6 magnitude green flash.

An enlargement of a telescopic image showing one of the jets emerging from the shape charge detonation flash in the upper left. (Caltech)

Subsequent evaluation of the data showed that two jets containing hypervelocity aluminum pellets were clearly observed propagating upwards. While the slower moving jet corresponding to a heavier metal slug was measured to be moving at only 3 to 5 kilometers per second and would arc back to Earth, the velocity of the particles in the brighter jet was at least 15 kilometers per second. Zwicky reasoned that since the atmosphere above 85 kilometers was so tenuous resulting in little loss in momentum, these particles would have surely exceeded Earth’s 11.2 kilometer per second escape velocity and proceeded into solar orbit. Although proving beyond any doubt that some of these particle were actually in solar orbit would be a real world example of Russell’s teapot orbiting somewhere between the planets (an analogy posited by philosopher Bertrand Russell to illustrate that the burden of proof lies upon a person making unfalsifiable claims), the analysis strongly supported the claim that the US had been the first to launch artificial objects into solar orbit.

Diagram showing the calculated trajectory of the fastest pellets propelled into solar orbit during the October 16, 1957 artificial meteor experiment. Click on image to enlarge. (Caltech)

After over a decade of effort, Zwicky’s artificial meteor experiment not only proved to be a success, it also provided the US with a much needed (albeit minor) morale boost in the wake of Sputnik. Although Zwicky had grand plans for further advancements of this technology to aid in the exploration of space, the world’s focus soon turned to more conventional rocketry to provide data on the space environment leaving this interesting footnote in the early history of the Space Age.

Zwicky’s artificial meteor experiment made headlines and helped provide at least a minor boost to American morale in the wake of the Sputnik launch.



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Related Reading

“Sputnik: The Launch of the Space Age”, Drew Ex Machina, October 4, 2017 [Post]


General References

David H. DeVorkin, Science with a Vengeance: How the Military Created the US Space Sciences after World War II, Springer-Verlag, 1992

Stephen M. Maurer, “Idea Man”, Beam Line, pp. 21,27, Winter 2001

Fritz Zwicky, “Research with Rockets”, Publications of the Astronomical Society of the Pacific, Vol. 59, No. 347, pp. 64-73, April 1947

Fritz Zwicky, “The First Shots into Interplanetary Space”, Engineering and Science, Vol. 20, No. 4, pp. 20-23, January 1958

“Artificial Meteor”, Sky & Telescope, Vol. 17, No. 3, p. 111, January 1958