OCR Vadim Anosov

Spectacular lift-off of Pioneer 5 from pad 17A at
Cape Canaveral on 11 March 1960.
The forgotten mission of Pioneer 5
By Joel Powell
Forty five years ago, in March of 1960, NASA launched a modest 94.8 pound sphere on a planetary trajectory toward the orbit of Venus. The objective of the Pioneer 5 mission was not the planet itself (Venus was not in position for an encounter), but rather a survey of environmental conditions in interplanetary space to demonstrate the feasibility of communicating with a spacecraft at great distances. At a time in the early Space Age when the farthest radio contact in space was barely beyond the Moon, the solar-powered Pioneer set a communication distance record of 22.5 million miles after surviving for three-and-a-half months after launch.

The Thor-Able IV launch vehicle of Pioneer 5 resided on pad 17A for five months after being stacked in October 1959.

45th anniversary of a pioneering space project

Present day space engineers take for granted the capability to contact farflung space probes in our solar system from Mercury to Pluto, but in 1960 the Deep Space Network did not yet exist, and NASA had to rely upon the British radio telescope at Jodrell Bank to maintain contact with Pioneer. It would be more than two years before the NASA deep space tracking stations were operational during the Mariner 2 mission to Venus, which was the first successful planetary encounter. Mariner 2 extended the long-distance communication record to 53.9 million miles in December 1962.

Pioneer 5 - trials and tribulations

The Pioneer 5 mission was conceived at Space Technology Laboratories (STL - a subsidiary of TRW Inc.) for NASA headquarters in November 1958, one of the first space projects planned for the newly chartered space agency (the lunar probes and Project Vanguard were inherited from the military). Pioneer 5 was eventually assigned to the new NASA space science laboratory at Greenbelt, Maryland, becoming the first deep space mission conducted by the Goddard Space Flight Center. The spacecraft was built for NASA by Space Technology Laboratories. STL's project director for Pioneer 5 was Dr Adolph K. Thiel, and Dr John C. Lindsay served as project manager for NASA. The original plan for Pioneer 5 was as audacious as it was impracticable: the tiny spacecraft would have been rocketed to Venus as a fly-by probe in tandem with a Venus orbiter to be launched on an Atlas-Able rocket in June 1959. The intention was to launch the missions one day apart (on 3 and 4 June 1959), but NASA was forced to abandon the plan when neither payload was ready by the spring of 1959.
NASA planners decided to re-target the Venus orbiter to Earth's Moon, with a planned launch date of 3 October 1959, but the payload (also named Pioneer) never even made it to the launch pad. On 24 September 1959, as Atlas rocket 9C was static fired at Cape Canaveral in preparation for the mission, a procedural error by the launch team resulted in the destruction of the rocket in a massive explosion.
The Pioneer 5 probe, which was fated to experience continual launch delays through the rest of 1959 and into 1960, alone remained to carry on NASA's fledgling space exploration program when Atlas-Able failed again in November 1959.

Solar power paddles of Pioneer 5 are extended during a deployment test inside upper level of the aantrv tower.
An ever-optimistic NASA hierarchy ordered the Air Force to stack the Thor-Able IV launch vehicle on pad 17A at Cape Canaveral in October 1959. Two launch dates in early December were derailed by reported electronic problems in the payload, and a tentative date of 28 January 1960 was further delayed to 1 March when NASA engineers ordered additional vibration tests and a vacuum chamber checkout for the payload. In late February a more realistic launch target window of 4-8 March was announced by NASA, which slipped a further three days to 11 March.
Finally at 8:00:05 am Eastern Time on 11 March 1960 the Thor-Able rocket roared to life and accelerated the beach-ball sized payload to a velocity of 24,869 mph (nearly 37,000 feet per second). The Pioneer 5 space "probe" - apparently the first use of the term - was on its way to interplanetary space.
Perihelion distance for Pioneer 5 was 74.9 million miles from the Sun, and aphelion was 92.3 million miles. Pioneer was originally intended by NASA for a 285 day solar orbit, but a 331 mph shortfall at launch resulted in a slightly elongated solar orbital period of 311.6 days.
Pioneer had two radio transmitters operating at a frequency of 378 megacycles (MHz), one a low-power 5 watt transmitter for use when the probe was close to Earth, and a 150 watt transmitter for use at longer distances. With 150 watts of electrical power generated by the four solar paddles, Pioneer 5 was the most energetic payload in space to date. Lack of additional power reserves limited communication with Earth to several brief sessions totaling about two hours per day.
Initial contact with Pioneer 5 was established by the American grid antenna at South Point, Hawaii. A malfunctioning diode disrupted radio operations shortly after launch, but full communications were restored by 24 April.

Scientific instruments and primitive radio equipment of Pioneer 5 are revealed in this cutaway illustration.
Lacking more sensitive facilities to contact Pioneer at greater distances, NASA arranged with the University of Manchester to use the 250 foot Jodrell Bank radio telescope in England (and NASA compensated the University at a rate of ?50 per hour according to Flight International magazine). On several occasions observatory director Sir Bernard Lovell permitted such notables as Princess Margaret and the Science Minister of the day to turn on the receiver to initiate contact with Pioneer.
Operation of the telemetry downlink was normal (except for the intermittent diode) until 30 April when the 150 watt transmitter was switched on. A problem with the probe's 28 storage batteries prevented Jodrell Bank from maintaining a lock on the distant space probe after that date. Careful analysis by NASA revealed that the batteries were slowly venting gas to space, possibly disrupting the stability of Pioneer and reducing power output.
Jodrell Bank managed to maintain sporadic contact with the probe until 26 June 1960, when the final contact was made at a distance of 22.5 million miles. Only the carrier wave signal was received back on Earth due to the battery venting problem.

Interplanetary science

Pioneer 5 carried four scientific instruments to characterize conditions in interplanetary space beyond our Moon. NASA scientists also analysed the radio signals from the probe to determine the Astronomical Unit, the average distance from the Earth to the Sun and the yardstick to judge distances in the solar system (expressed in terms of solar parallax) to a new degree of accuracy. Measurements were also made of cosmic ray flux and the flow of charged particles (now recognized as the "solar wind") to a distance of about 17.7 million miles, the point at which telemetry encoding was lost.
Tantalising data was also collected regarding magnetic fields in space, but the micrometeorite detector failed to operate properly. Every space probe that followed Pioneer 5 in the next ten years had similar suites of instruments to explore interplanetary space, and a series of four NASA spacecraft also named Pioneer were launched from 1965 to 1968 to monitor the behaviour of the solar wind in deep space.
The backup Pioneer 5 payload still resides in the collection of the National Air and Space Museum in Washington. Pioneer 5 was a welcome success for the new American space agency in the third year of the Space Age. The communication distance record established by Pioneer 5 in 1960 demonstrated American technical prowess, and helped restore a measure of America's space reputation while proving the feasibility of interplanetary radio communication.

White and black painted sections on the 26 inch spherical Pioneer 5 payload helped to regulate internal temperature.

The radio telescope at Jodrell Bank in Cheshire, England, which was used by NASA to track Pioneer. The telescope maintained sporadic contact with the probe until 26 June 1960 when final contact was made a distance of 22.5 million miles. Manchester University