The spacecraft consisted of two laminated plastic cones with a thin cylinder in the middle. Black or white plastic stripes were used for thermal control. At the top of the spacecraft was a retro-rocket for lunar orbit insertion. In the other end eight small low-thrust solid propellant velocity adjustment rockets were mounted on a ring. They could be jettisoned after use. The instrument section consisted of an infra-red TV camera, a magnetometer, a simple micrometeroid impact detector and a radiation detector.
A programming error in the Pioneer 1 launch vehicle upper stage resulted in Pioneer 1 being given insufficient velocity to escape the Earth's gravitational field. Although Pionner 1 newer reached lunar orbit, it was not a complete failure. In fact it did reach an altitude of 113854 km above Earth (A record at that time) and provided data on the extent of the Earth's radiation belts. The vehicle reentered over the Pacific Ocean 2 days later.