Before American astronauts ventured beyond the Earth, scientists and engineers had to assess the nature of the space environment and the hazards of human exploration. In early 1959—just after the start of Project Mercury and during selection of the seven Mercury astronauts—the Pioneer IV space probe was launched into orbit around the sun, and two monkeys, Able and Baker, made a 579-kilometer (360-mile) high sub-orbital flight.
On March 3, 1959, the U.S. launched the Pioneer IV space probe, boosted by a four-stage Juno II rocket. For 82 hours on-board instruments transmitted measurements of radiation in space. When the batteries went dead, the probe was 654,900 kilometers (407,000 miles) from Earth. Mission planners designed Pioneer IV to pass within 32,000 kilometers (20,000 miles) of the Moon. It carried a photoelectric sensor to be triggered by moonlight in a test for future photographic missions.
To accomplish this mission, the speed and trajectory of the probe had to be within precise targets. The launch speed was 302.7 kilometers (188 miles) per hour too slow and the probe passed the Moon at 60,016 kilometers (37,300 miles)—too far away for the sensor to work. Pioneer IV was the second object sent into solar orbit from Earth. Two months earlier the Soviet Union's Mechta rocket had passed 5,953 kilometers (3,700 miles) from the Moon and had been tracked to a distance of 542,200 kilometers (337,000 miles) from Earth.
This is the back-up Pioneer IV instrument package.* The conical antenna, lifted here to show the instruments, is made of fiberglass and sprayed with gold. The alternating black and gold stripes help maintain a proper internal temperature by controlling the amount of heat absorbed from sunlight.
On the top of the instrument package are two Geiger-Mueller tubes that measured radiation. One is shielded so that only high-energy particles can register. Beneath the tubes is supporting circuitry, a radio transmitter enclosed in a central band of batteries, and the lens of a photoelectric scanning device. This lens was designed to trigger a signal to Earth when it "saw" the far side of the Moon. This compact design weighed 6.26 kilograms (13.8 pounds).
On May 28, 1959, the Army Ballistic Missile Agency lifted two monkeys into space on a suborbital mission in a Jupiter missile nose cone to test physiological reactions to spaceflight. The test took its name from the two monkeys, Able, a 3.18 kilogram (7-pound) rhesus monkey, and Baker, a 311.9 gram (11-ounce) squirrel monkey. In 16 minutes, the nose cone traveled 2,735 kilometers (1,700 miles) from Cape Canaveral and reached an altitude of approximately 579 kilometers (360 miles).
The two monkeys survived the flight in good condition. Able, however, died 4 days later from a reaction to the anesthetic given during surgery to remove an infected electrode. Baker died on Nov. 29, 1984, in Huntsville, Alabama of kidney failure at the age of 27. The flight contained seven other experiments. Sea urchin eggs, human blood cells, yeast and onion skin cells, corn seeds, mustard seeds, mold spores, and fruit fly larvae were exposed to cosmic rays and returned to Earth for study.
Able, the larger of the two monkeys on the Able-Baker mission, was a 3.18 kilogram (7-pound) rhesus monkey.
Able's fiberglass couch, lined with polyurethane foam, held her in a position similar to that which was to be used by the Mercury astronauts.
Able, preserved after her death, is displayed here in her specially-designed couch, which fit inside a protective capsule.
During the flight, a 16mm movie camera photographed Able, while her biological reactions were telemetered to ground recording stations on Earth.
As part of a physiological experiment, scientists planned to have the rhesus monkey press a telegraph key (under the right paw) when a light flashed. The rhesus monkeys initially trained for the mission, however, were born in India where the rhesus is sacred and are not used as experimental animals. To avoid diplomatic repercussions, the American-born Able was substituted, two weeks before the mission. As she did not have time to learn her drill, the experiment was cancelled. The Able Experiment was a project of the U.S. Army Medical Research and Development Command.
The smaller squirrel monkey, Baker, also was transported in a specially-designed restraint, cushioned with polyurethane foam. The end of the couch cylinder has molded rubber pads to absorb jolts, while the couch foam absorbed high-frequency vibrations.
Baker's biological reactions were telemetered to ground recorders. The Baker Experiment was a project of the U.S. Naval School of Aviation Medicine.