Pioneer Venus Orbiter was designed to perform long-term observations of the Venusian atmosphere and surface features. After entering orbit around Venus in 1978, the Pioneer spacecraft returned global maps of the planet's clouds, atmosphere and ionosphere, measurements of the atmosphere-solar wind interaction, and radar maps of 93 percent of the surface of Venus. Additionally, the vehicle made use of several opportunities to make systematic UV observations of several comets. With a planned primary mission duration of only eight months, the Pioneer spacecraft remained in operation until October 8, 1992 when it finally burned up in the atmosphere of Venus after running out of propellant. Data from the Orbiter was correlated with data from its sister vehicle (Pioneer Venus Multiprobe and its atmospheric probes) to relate specific local measurements to the general state of the planet and its environment as observed from orbit.
Despite their drastically different roles, the Pioneer Orbiter and Multiprobe were very similar in design. The use of identical systems (including flight hardware, flight software, and ground test equipment) and incorporation of existing designs from previous missions (including OSO and Intelsat) allowed the mission to meet its objectives at minimum cost.
Spacecraft
Spin stabilized at ~15 rpm. Body mounted solar panels provided 312 W. 2 7.5 Ah NiCd batteries. A 1.09 m despun dish antenna used for high rate S-band communication with Earth, with low-gain omni antennas for emergency communication. 4 10W TWTAs. An X-band transmitter also incorporated for occultation measurements. Attitude determination provided by sun sensors and star sensors. Nutation damping performed with a partially filled tube of liquid Freon. Hydrazine propellant system with 7 thrusters used for attitude control and orbit adjustment. A solid rocket motor providing 18,000 N of thrust used for Venus orbit insertion. 4.8 m deployable boom for the magnetometer.
Payload
Pioneer Venus Orbiter carried 17 experiments (with a total mass of 45 kg). Most of the instruments were still operating when the spacecraft entered the atmosphere:
- Cloud photopolarimeter - measured the vertical distribution of the clouds
- Surface radar mapper - mapped planetary topography and surface characteristics
- Infrared radiometer - monitored IR emissions from the Venusian atmosphere
- Airglow ultraviolet spectrometer - measured scattered and emitted UV radiation
- Neutral mass spectrometer - evaluated the composition of the upper atmosphere
- Solar wind plasma analyzer - measured properties of the solar wind
- Magnetometer - examined Venus' magnetic field
- Electric field detector - studied the solar wind and its interactions with the Venusian atmosphere
- Electron temperature probe - examined the thermal properties of Venus' ionosphere
- Ion mass spectrometer - measured the ionospheric ion population
- Charged particle retarding potential analyzer - Studied ionospheric particles
- 2 radio science experiments - mapped Venus' gravity field
- Radio occultation experiment - helped characterize the atmosphere
- Atmospheric drag experiment - upper atmosphere density measurements
- Radio science atmospheric and solar wind turbulence experiment
- Gamma ray burst detector - monitored gamma ray burst events
