Pioneer 5
Pioneer 5 mounted to its Thor Able launcher.
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| Mission type | Interplanetary space research |
|---|---|
| Operator | NASA |
| Harvard designation | 1960 Alpha 1 |
| SATCAT no. | 27 |
| Spacecraft properties | |
| Manufacturer | TRW |
| Launch mass | 43 kilograms (95 lb) |
| Start of mission | |
| Launch date | March 11, 1960, 13:00:07 UTC |
| Rocket | Thor DM-18 Able IV |
| Launch site | Cape Canaveral LC-17A |
| End of mission | |
| Last contact | April 30, 1960 |
| Orbital parameters | |
| Reference system | Heliocentric |
| Eccentricity | 0.1689 |
| Perihelion | 0.7061 astronomical units (105,630,000 km; 65,640,000 mi) |
| Apohelion | 0.9931 astronomical units (148,570,000 km; 92,310,000 mi) |
| Inclination | 3.35 degrees |
| Period | 311.6 days |
Pioneer 5 (also known as Pioneer P-2, and Thor Able 4) was a spin-stabilized space probe in the NASA Pioneer program used to investigate interplanetary space between the orbits of Earth and Venus. It was launched on March 11, 1960 from Cape Canaveral Air Force Station Launch Complex 17A at 13:00:00 UTC with an on-orbit dry mass of 43 kg. It is a 0.66 m diameter sphere with 1.4 m span across its four solar panels and achieved a solar orbit of 0.806 × 0.995 AU (121,000,000 by 149,000,000 km).
Data was received until April 30, 1960. Among other accomplishments, the probe confirmed the existence of interplanetary magnetic fields.Pioneer 5 was the most successful probe in the Pioneer/Able series.
The original mission plan was for a launch in November 1959 where Pioneer 5 would conduct a flyby of Venus, but technical issues prevented the launch from occurring until early 1960 by which time the Venus window for the year had closed. Since it was not possible to send the probe to Venus, it would instead merely investigate interplanetary space and an actual mission to the planet would have to wait another three years.
The spacecraft was a 0.66 m diameter sphere with four solar panels that spanned over 1.4 m. It was equipped with four scientific instruments:
Booster performance during launch was overall excellent considering the numerous earlier difficulties with the Thor-Able vehicle. There were some minor anomalies with the second stage flight control system that resulted in unplanned pitch and roll motions, however they were not enough to endanger the mission.
The spacecraft returned data collected by the magnetometer on the magnetic field and it measured that the median undisturbed interplanetary field was approximately 5 γ ± 0.5 γ in magnitude. The spacecraft also measured solar flare particles, and cosmic radiation in the interplanetary region. The micrometeorite counter failed to operate as the data system saturated and failed to operate properly.
The recorded digital data were transmitted at 1, 8, and 64 bit/s, depending on the distance of the spacecraft from Earth and the size of the receiving antenna. Weight limitations on the solar cells prevented continuous operation of the telemetry transmitters. About four operations of 25 min duration were scheduled per day with occasional increases during times of special interest. A total of 138.9 h of operation was completed, and over three megabits of data were received. The major portion of the data was received by the Lovell radio telescope at Jodrell Bank Observatory and the Hawaii Tracking Station because their antennas provided grid reception. Data was received until April 30, 1960, after which telemetry noise and weak signal strength made data reception impossible. The spacecraft's signal was detected by Jodrell Bank from a record distance of 36.2 million km (22.5 million miles) on June 26, 1960, although it was much too weak by then to acquire data.
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