[5] Pioneer 1 was fabricated by Space Technology Laboratories, a division of Ramo-Wooldridge Corp (later TRW Inc.),[6] and consisted of a thin cylindrical midsection with a squat truncated cone on each side.

The three-stage Thor-Able vehicle consisted of a modified Air Force Thor IRBM (liquid propellant, thrust about 69,400 kg (153,000 lb)) as the first stage.

[7] The scientific instrument package had a mass of 17.8 kg (39 lb) and consisted of an image scanning infrared television system to study the Moon's surface to a resolution of 0.5°, an ionization chamber to measure radiation in space, a diaphragm/microphone assembly to detect micrometeorites, a spin-coil magnetometer to measure magnetic fields to 5 microgauss, and temperature-variable resistors to record the spacecraft's internal conditions.

On 11 October 1958, Pioneer 1 lifted off smoothly, but the guidance system steered the Thor slightly too high and fast, causing the second stage to be lofted 3° higher than intended.

The vernier engines on the third stage were fired to make up for the thrust deficit, but added only 150 feet per second of velocity, insufficient to escape Earth orbit.

As a last resort, ground controllers decided that if they could not get Pioneer 1 to the Moon, they would place it in a high Earth orbit by firing the attached solid rocket motor.

The inaccurate launch trajectory, however, had placed the probe on an orbital track that resulted in thermal heating and cooling beyond what the primitive temperature control system could handle.