Mission Type: Impact
Launch Vehicle: Atlas-Centaur (AC-51 / Atlas no. 5031D)
Launch Site: ETR / launch complex 36A
NASA Center: Ames Research Center
Spacecraft Mass: 904 kg
Spacecraft Instruments:
Bus:
1) neutral mass spectrometer
2) ion mass spectrometer
3) differential long baseline interferometry experiment
4) atmospheric propagation experiment
5) atmospheric turbulence experiment
Large probe:
1) neutral mass spectrometer
2) solar flux radiometer
3) gas chromatograph
4) infrared radiometer
5) cloud particle size spectrometer
6) atmospheric structure experiment
Small probes (each):
1) atmospheric structure experiment
2) cloud particles experiment
3) net flux radiometer
References:
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, by Asif A. Siddiqi, NASA Monographs in Aerospace History No. 24

Pioneer Venus 2, the twin to Pioneer Venus 1, comprised a main bus, a large probe (316.5 kg), and three identical small probes, all of which were designed to collect data during independent atmospheric entry into Venus. Each probe was shaped like a cone and not designed to survive past surface impact.

After a course correction on 16 August 1978, Pioneer Venus 2 released the 1.5-m diameter large probe on 16 November 1978, at about 11.1 million km from the planet. Four days later, the bus released the three small probes while 9.3 million km from Venus. All five components reached the Venusian atmosphere on 9 December 1978, with the large probe entering first.

Using a combination of air drag and a parachute, the large probe descended through the atmosphere until it impacted on the Venusian surface at 4.4ý north latitude and 304.0ý longitude at a speed of 32 km per hour. Transmissions ceased at impact as expected.

The three 76-cm diameter small probes arrived in the atmosphere within minutes of the bigger one and descended rapidly through the atmosphere without the benefit of parachutes. Amazingly, two of three probes survived the hard impact.

The so-called Day Probe transmitted data from the surface for 67.5 minutes before succumbing to the high temperatures and power depletion.

All three small probes suffered instrument failures, but none significant enough to jeopardize their main missions. Their landing coordinates were 59.3ý north latitude and 4.8ý longitude (North Probe); 31.3ý south latitude and 317.0ý longitude (Day Probe); and 28.7ý south latitude and 56.7ý longitude (Night Probe). The main bus, meanwhile, burned up in the atmosphere at an altitude of 120 km -- about 1.5 hours after the other probes -- and provided key data on higher regions.

Data from the probes indicated that between 10 and 50 km, there is almost no convection in the atmosphere. Below a haze layer at 30 km, the atmosphere appears to be relatively clear.

Editor's Note: This mission profile was adapted from a mission profile originally published in Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, by Asif A. Siddiqi, NASA Monographs in Aerospace History No. 24