Mission Type: Orbiter
Launch Vehicle: Thor-Able I (no. 1 / Thor no. 130 / DM-1812-6)
Launch Site: Cape Canaveral, United States, launch complex 17A
Spacecraft Mass: 38.3 kg
Spacecraft Instruments: 1) ionization chamber; 2) magnetometer; 3) micrometeoroid detector; 4) NOTS infrared imaging system and 5) temperature sensor
References:
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Monographs in Aerospace History No. 24, by Asif A. Siddiqi

National Space Science Data Center, http://nssdc.gsfc.nasa.gov/

Although the USAF actually conducted the mission, this was the first U.S. space mission under the aegis of the recently formed National Aeronautics and Space Administration (NASA).

The spacecraft was very similar in design to the Able 1 probe. During the mission, the Thor second stage shut down 10 seconds early due to incorrect information from an accelerometer measuring incremental velocity. The launch vehicle thus imparted insufficient velocity for the probe to escape the Earths gravity.

An attempt to insert the spacecraft into high- Earth orbit at 128,700 x 32,200 kilometers by using its retromotor failed because internal temperatures had fallen too much for the batteries to provide adequate power.

The probe did, however, reach an altitude of 115,400 kilometers by 11:42 UT, verifying the existence of the Van Allen belts and returned other useful data before reentering 43 hours
17 minutes after launch.

Investigators later concluded that an accelerometer had mistakenly cut off the Able stage because of an incorrect setting of a valve. The mission has been retroactively known as Pioneer 1.