Venus Multiprobe Credit - NASA

The Pioneer Venus Multiprobe consisted of a bus which carried one large and three small atmospheric probes. . After release from the carrier vehicle, the probes entered the atmosphere at 41,600 km/hr, followed by the bus. The small probes were each targeted at different parts of the planet and were named accordingly.

The North probe entered the atmosphere at about 60 degrees north latitude on the day side. The night probe entered on the night side. The day probe entered well into the day side, and was the only one of the four probes which continued to send radio signals back after impact, for 67 minutes. The carrier vehicle, not designed for atmospheric re-entry, followed the probes into the Venusian environment and relayed data about the characteristics of the extreme outer atmosphere until it was destroyed by atmospheric heating. Despite their drastically different roles, the 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

• Multiprobe bus (Carrier vehicle) - With no heat shield or parachute, the bus survived and made measurements only to about 110 km altitude before burning up. The bus was a 2.5 m diameter cylinder weighing 290 kg. Spin stabilized. Body mounted solar panels provided 241 W. Payloads: Ion Mass Spectrometer (BIMS) - studied the composition of the upper atmosphere. Neutral Mass Spectrometer (BNMS) - studied the composition of the upper atmosphere.

• Large probe - Weighed 315 kg. Consisted of 3 parts: a forward heat shield, an aft protective cover and a spherical titanium pressure vessel (73 cm diameter). Total probe diameter was 1.5 m. After deceleration from initial atmospheric entry at about 11.5 km/s near the equator on the Venus night side, the heat shield and protective cover were jettisoned, and a parachute was deployed at 47 km altitude to further slow descent. After parachute deployment, the exposed pressure vessel and its instrument package descended for about 1 1/2 hour before impact. During descent, the instruments were powered by batteries. Nine observation windows (8 sapphire and 1 diamond) were provided for instrument observations.3 pressure vessel penetrations were also provided as inlets for direct atmospheric sampling. Payload: Atmospheric Structure (LAS). Nephelometer (LN) - studied cloud particles. Cloud Particle Size Spectrometer (LCPS) - measured particle size and shape. Gas Chromatograph (LGC) - studied atmospheric composition. Infrared Radiometer (LIR) - monitored the distribution of infrared radiation. Neutral Particle Mass Spectrometer (NPMS) - studied atmospheric composition. Solar Flux Radiometer (LSFR) - examined solar flux penetration into the atmosphere. Differential Long Base Line Interferometer (DLBI). Atmospheric Propagation (MPRO) - temperature, pressure, and acceleration measurements.

• Small probes - Each probe weighed 75 kg and was 0.8 m in diameter. Consisted of 3 parts: a forward heat shield, an aft protective cover and a spherical titanium pressure vessel. Unlike the large probe, the heat shield and protective cover remained attached to the pressure vessel, and no parachutes were deployed. Prior to atmospheric entry, each probe deployed a yo-yo despin device to reduce its spin rate from 48 to 15 rpm. Batteries provided power during descent (which lasted approx.75 minutes). Payload: Nephelometer. Temperature, pressure, and acceleration sensors. Net flux radiometer - mapped the distribution of sources and sinks of radiative energy in the atmosphere. Radio signals from all four probes were also used to characterize winds, turbulence, and propagation in the atmosphere.

Design Life: 4 months. Typical orbit: Venus direct trajectory. Length: 2.90 m (9.50 ft). Maximum Diameter: 2.50 m (8.20 ft).

• 1978 August 8 - Pioneer Venus 2 - Program: Pioneer. Launch Site: Cape Canaveral. Launch Complex: LC36A. Launch Vehicle: Atlas. Mass: 904 kg (1,992 lb).
  The Pioneer Venus Multiprobe consisted of a bus which carried one large and three small `atmospheric probes. The large probe was released on November 16, 1978 and the three small probes on November 20. All four probes entered the Venus atmosphere on December 9, followed by the bus. The small probes were each targeted at different parts of the planet and were named accordingly. The North probe entered the atmosphere at about 60 degrees north latitude on the day side. The night probe entered on the night side. The day probe entered well into the day side, and was the only one of the four probes which continued to send radio signals back after impact, for over an hour. With no heat shield or parachute, the bus survived and made measurements only to about 110 km altitude before burning up. It afforded the only direct view of the upper Venus atmosphere, as the probes did not begin making direct measurements until they had decelerated lower in the atmosphere.

• 1978 August 8 - Pioneer Venus Probe 1 - Program: Pioneer. Launch Site: Cape Canaveral. Launch Complex: LC36A. Launch Vehicle: Atlas. Mass: 315 kg (694 lb).
  

• 1978 August 8 - Pioneer Venus Probe 2 - Program: Pioneer. Launch Site: Cape Canaveral. Launch Complex: LC36A. Launch Vehicle: Atlas. Mass: 90 kg (198 lb).
  

• 1978 August 8 - Pioneer Venus Probe 3 - Program: Pioneer. Launch Site: Cape Canaveral. Launch Complex: LC36A. Launch Vehicle: Atlas. Mass: 90 kg (198 lb).
  

• 1978 August 8 - Pioneer Venus Probe 4 - Program: Pioneer. Launch Site: Cape Canaveral. Launch Complex: LC36A. Launch Vehicle: Atlas. Mass: 90 kg (198 lb).
  

• 1978 December 9 - Pioneer Venus 2, Venus Atmospheric Probes -