Able 2. The first NASA mission.

 
Project Able-1 lunar probe. Credit: NASA

 
Able 2 was the second in the series of three lunar probes with the ambitious goal of being the first spacecraft to orbit the Moon. The program, under the name of Project Able-1, was officially approved on March 27, 1958, as part of scientific investigations during the International Geophysical Year. It was initially under the supervision of the Advanced Research Projects Agency (ARPA). The probes were constructed by Space Technology Laboratories (STL). The first attempted launch, on August 17, 1958, ended when the launch vehicle was destroyed by an explosion of the first stage of the Thor booster, 73.6 seconds after lift-off. 

   In September 1958, the program was transferred from ARPA to the recently formed National Aeronautics and Space Administration (NASA). Able 2 was the first space mission under the direction of NASA, but it was actually conducted by the United States Air Force. After the launch, the mission was officially named Pioneer.  
 
Technicians preparing a Project Able-1 lunar orbiter under sterile conditions to minimize the risk of contaminating the Moon. Credit: STL

   The spacecraft was nearly identical to its predecessor except for the addition of an ion counter. It consisted of a thin cylindrical midsection with a diameter of 74 centimeters and two squat truncated cones on both sides. The height from the top of one cone to the top of the opposite cone was 76 cm. The solid propellant retrorocket was designed to decelerate the spacecraft into lunar orbit. The spacecraft also had eight small vernier rockets for velocity adjustments. 

   There were four scientific instruments on board: infrared scanning TV camera to study the Moon's surface, ion chamber, magnetometer and a diaphragm/microphone micrometeoroid detector. Two temperature sensors recorded spacecraft internal conditions. The probe had a total mass of 38.3 kg. The spacecraft's launch vehicle was a Thor Able I (Thor no. 130) three-stage rocket. 

Diagram showing equipment inside Pioneer 1 probe. Credit: STL
 
   Able 2 was launched from Pad 17A at Cape Canaveral on October 11, 1958, at 08:42:13 UT. At the time of first stage cutoff, the rocket was flying too fast and a little of course, the second stage shut down 10 seconds early due to incorrect information from an accelerometer, and the third stage was pushed off course. As a result the achieved velocity was about 150 meters per second slower than required and 5 degrees off course. Subsequently, all eight vernier rockets were fired in an attempt to make up the velocity deficit and they added some 50 meters per second, but the escape velocity from Earth’s gravity was not achieved. 
 
Artist’s conception of the Able-1 spacecraft in flight firing its vernier engines. Credit: STL
 
   21,5 hours after launch the probe reached maximum altitude of about 113,810 km  (or according to other estimates 115,400 km). An attempt was made to convert the probe into a high altitude satellite by firing its retrorocket, but because internal temperatures had fallen too low, the batteries were incapable of supplying the ignition current. The probe reentered Earth’s atmosphere over the South Pacific Ocean 43 hours and 17 minutes after launch.

   Pioneer I did not reach its intended goal, the vicinity of the Moon, but returned much useful scientific information, especially about the extent of the Van Allen radiation belts and the micrometeoroid flux in space. The probe was also used for the first tests of satellite communications with telemetry being relayed through Pioneer between tracking stations on Earth.
 
Thor-Able I with Pioneer I spacecraft atop, prior to launch. Credit: NASA

Pioneer I lift-off from Pad 17A at Cape Canaveral. Credit: USAF
 
Diagram of the orbit of Pioneer I. Credit: STL
 
 

References:

Asif A. Siddiqi. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. Washington, DC: NASA History Program Office, 2018. ISBN 978-1-62683-042-4
Gideon Marcus. Pioneering Space. Quest, Vol. 14, No. 2, pp. 52-59, 2007
Gideon Marcus. Pioneering Space – Part II. Quest, Vol. 14, No. 3, pp. 18-25, 2007
Space Technology Laboratory. 1958 NASA/USAF Space Probes (Able-1) Final Report: Volume 1 – Summary. February 18, 1959
Space Technology Laboratory. 1958 NASA/USAF Space Probes (Able-1) Final Report: Volume 2 – Payload and Experiments. February 18, 1959
Space Technology Laboratory. 1958 NASA/USAF Space Probes (Able-1) Final Report: Volume 3 – Vehicles, Trajectories, and Flight Histories. February 18, 1959

 

 © 2025, Andrew Mirecki

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