What was Able 5B (Pioneer P-31)?

LIke its two unsuccessful predecessors, this U.S. spacecraft was launched to orbit the Moon. Unfortunately, the Atlas Able booster malfunctioned and exploded a few seconds after launch.

• The payload fell into the Atlantic Ocean about 7 to 12 miles (12 to 20 kilometers) from Cape Canaveral, Florida.
• This was the third and last attempt by NASA to launch a probe to orbit the Moon in the 1959–1960 period.

Nation	United States of America (USA)
Objective(s)	Lunar Orbit
Spacecraft	Pioneer P-31 / Able 5B
Spacecraft Mass	388 pounds (176 kilograms)
Mission Design and Management	NASA / U.S. Air Force Ballistic Missile Division
Launch Vehicle	Atlas Able (Atlas Able no. 3 / Atlas D no. 91)
Launch Date and Time	Dec. 15, 1960 / 09:11 UT
Launch Site	Cape Canaveral Air Force Station, Fla. / Launch Complex 12
Scientific Instruments	Micrometeoroid Detector High-Energy Radiation Counter Ionization Chamber Geiger-Mueller Tube Low-Energy Radiation Counter Flux-Gate Magnetometer and a Spinsearch Coil Magnetometer Sun Scanner Plasma Probe Scintillation Spectrometer Solid State Detector

Key Dates

Dec. 15, 1960: Launch

Dec. 15, 1960: Spacecraft destroyed seconds after launch

In Depth: Able 5B (Pioneer P-31)

The mission of Able 5B, like its two unsuccessful predecessors, was to orbit the Moon.

Scientific objectives included studying radiation near the Moon, recording the incidence of micrometeoroids, and detecting a lunar magnetic field.

Planned lunar orbital parameters, to be achieved about 60 hours after launch, were 2,700 × 1,500 miles (4,300 × 2,400 kilometers) with an orbital period of 9 to 10 hours.

The spacecraft had a slightly different scientific instrument complement than its predecessors, including a plasma probe experiment designed by NASA’s Ames Research Center that was to provide data on the energy and momentum distribution of streams of protons with energies above a few kilovolts per particle in the vicinity of the Moon.

Unfortunately, the Atlas Able booster suffered a malfunction 66.68 seconds after launch and then exploded at T+74 seconds at an altitude of about 7.5 miles (12.2 kilometers).

An investigation indicated that the Able upper stage prematurely ignited while the first stage was still firing.

This was the third and last attempt by NASA to launch a probe to orbit the Moon in the 1959–1960 period.

Additional Resources

National Space Science Data Center Master Catalog: Pioneer P-31

Key Source

Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.