Designed to supersede the German V-2 as a research vehicle, the Viking was the most advanced large, liquid-fueled rocket developed in the United States in the late 1940s, providing much engineering experience while returning valuable scientific data from the edge of space between 1949 and 1955.

After World War II, the United States Army experimented with captured German V-2 rockets as part of the Hermes program.

Both were actively guided rockets, fueled with the same propellant (Ethyl alcohol and liquid oxygen), which were fed to a single large pump-fed engine by two turbine-driven pumps.

The rotation of the engine on the gimbals was controlled by gyroscopic inertial reference; this type of guidance system was invented by Robert H. Goddard amongst others, who had partial success with it before World War II intervened.

[1]: 231 Vikings 1 through 7 were slightly longer (about 15 m (49 ft)) than the V-2, but with a straight cylindrical body only 81 centimetres (32 in) in diameter, making the rocket quite slender.

[1]: 98–102 The fix worked, and Viking 3, launched 9 February 1950 and incorporating an integrated (rather than discrete) oxygen tank, reached 50 mi (80 km) and could have gone higher.

}[5]: 255  On 10 May 1950, from a site in the Pacific Ocean between Jarvis Island and Kiritimati, the fourth Viking became the first sounding rocket ever launched from a sea-going vessel.

[1]: 108–114 Viking 5, launched 21 November 1950 carried a vast array of photomultiplier tubes, ionization chambers and Geiger counters, for the detection of radiation across a wide variety of energies and types.

The rocket also carried two movie cameras to take high altitude film of the Earth all the way to its peak height of 108 miles (174 km) as well as Pirani gauges to measure air densities in the upper atmosphere.

[1]: 148, 236 Viking 6, launched 11 December, carried a much lighter payload, but its experiments included a battery of custom built pressure gauges.

After it was allowed to fly for 55 seconds in the hope that it would clear the immediate area and thus pose no danger to ground crew, Nat Wagner, head of the "Cutoff group", delivered a command to the rocket to cease its thrust.

In addition to cameras that photographed the Earth during flight, Viking 9 carried a full suite of cosmic ray, ultraviolet, and X-ray detectors, including sixteen plates of emulsion gel for tracking the path of individual high energy particles.

Lieutenant Joseph Pitts, a member of the launch team, shot a rifle round into the tank, equalizing the pressure and saving the rocket.

The launch team was able to salvage the instrument package of cameras, including X-ray detectors, cosmic ray emulsions, and a radio-frequency mass-spectrometer, valued at tens of thousands of dollars, although there was concern that the rocket was irreparable.

Data was received from the rocket for all stages of the flight, and its scientific package, including an emulsion experiment, returned the first measurement of positive ion composition at high altitudes.

Forty seconds into the flight, several puffs of smoke issued from the vehicle, but these accidental excitations of the rocket's roll jets did no harm.

[8] The Viking series returned a bonanza of scientific information measuring temperature, pressure, density, composition and winds in the upper atmosphere and electron density in the ionosphere, and recording the ultraviolet spectra of the Sun,[1]: 234  The success of the program, at a cost of under $6 million, suggested that, with a more powerful engine and the addition of upper stages, the Viking rocket could be made a vehicle capable of launching an Earth satellite.

[9]: 283 In October 1952, the General Assembly of the International Council of Scientific Unions (ICSU) adopted a proposal to undertake simultaneous observations of geophysical phenomena over the entire surface of the Earth.

The International Geophysical Year (IGY), set for 1957–58, would involve the efforts of a multitude of nations in such farflung regions as the Arctic and Antarctica.

On 8 June, United States Secretary of Defense Charles Wilson directed Assistant Secretary Donald A. Quarles to coordinate the implementation of a satellite program, with the United States Department of Defense providing the rocket and launch facilities, and the civilian IGY National Committee producing the satellite and its experimental package, the National Science Foundation being intermediary between the two agencies.

A committee, under the chairmanship of Homer J. Stewart of Jet Propulsion Laboratory, was developed to manage the project to weigh and choose between the available satellite orbiting options.