Pioneer Venus Multiprobe

Pioneer Venus Multiprobe

Pioneer Venus Multiprobe
Mission type	Venus atmospheric probe
Operator	NASA Ames
COSPAR ID	1978-078A
SATCAT №	11001
Website	National Space Science Data Center (NASA)
Mission duration	4 months, 1 day
Spacecraft properties
Bus	HS-507
Manufacturer	Hughes
Launch mass	290 kilograms (640 lb) (bus) 315 kilograms (694 lb) (large probe) 3 x 90 kilograms (200 lb) (small probes)
Power	241 watts
Start of mission
Launch date	August 8, 1978, 07:33 (1978-08-08UTC07:33Z) UTC
Rocket	Atlas SLV-3D Centaur-D1AR
Launch site	Cape Canaveral LC-36A
End of mission
Last contact	December 9, 1978, 20:22:55 UTC (bus) December 9, 1978, 20:55:34 (1978-12-09UTC20:55:35Z) UTC (day probe)
Orbital parameters
Reference system	Heliocentric
Venus atmospheric probe
Spacecraft component	Large Probe
Atmospheric entry	December 9, 1978, 18:45:32 UTC
Impact date	19:39:53 UTC
Impact site
Venus atmospheric probe
Spacecraft component	North Probe
Atmospheric entry	December 9, 1978, 18:49:40 UTC
Impact date	19:42:40 UTC
Impact site
Venus atmospheric probe
Spacecraft component	Day Probe
Atmospheric entry	December 9, 1978, 18:52:18 UTC
Impact date	19:47:59 UTC
Impact site
Venus atmospheric probe
Spacecraft component	Night Probe
Atmospheric entry	December 9, 1978, 18:56:13 UTC
Impact date	19:52:05 UTC
Impact site
Venus atmospheric probe
Atmospheric entry	December 9, 1978, 20:21:52 UTC

The Pioneer Venus Multiprobe, also known as Pioneer Venus 2 or Pioneer 13 was a spacecraft launched in 1978 to explore Venus as part of NASA's Pioneer program.

Spacecraft

Pioneer Venus Bus with probes attached

The Pioneer Venus Multiprobe bus was constructed by the Hughes Aircraft Company, built around the HS-507 bus. It was cylindrical in shape, with a diameter of 2.5 metres (8 ft 2 in) and a mass of 290 kilograms (640 lb). Unlike the probes, which did not begin making direct measurements until they had decelerated lower in the atmosphere, the bus returned data on Venus' upper atmosphere.

The bus was targeted to enter the Venusian atmosphere at a shallow entry angle and transmit data until destruction by the heat of atmospheric friction. The objective was to study the structure and composition of the atmosphere down to the surface, the nature and composition of the clouds, the radiation field and energy exchange in the lower atmosphere, and local information on the atmospheric circulation pattern. With no heat shield or parachute, the bus made upper atmospheric measurements with two instruments, an Ion Mass Spectrometer (BIMS) and a Neutral Mass Spectrometer (BNMS), down to an altitude of about 110 km before disintegrating on December 9, 1978.

Probes

The spacecraft carried one large and three small atmospheric probes, designed to collect data as they descended into the atmosphere of Venus. The probes did not carry photographic instruments, and were not designed to survive landing - the smaller probes were not equipped with parachutes, and the larger probe's parachute was expected to detach as it neared the ground. All four probes continued transmitting data until impact; however, one survived and continued to transmit data from the surface.

Large probe

Pioneer Venus Large Probe opens its parachute

The Large probe carried seven experiments, contained within a sealed spherical pressure vessel. The science experiments were:

• a neutral mass spectrometer to measure the atmospheric composition
• a gas chromatograph to measure the atmospheric composition
• a solar flux radiometer to measure solar flux penetration in the atmosphere
• an infrared radiometer to measure distribution of infrared radiation
• a cloud particle size spectrometer to measure particle size and shape
• a nephelometer to search for cloud particles
• temperature, pressure, and acceleration sensors

This pressure vessel was encased in a nose cone and aft protective cover. After deceleration from initial atmospheric entry at about 11.5 kilometres per second (7.1 mi/s) near the equator on the night side of Venus, a parachute was deployed at 47 km altitude. The large probe was about 150 centimetres (59 in) in diameter and the pressure vessel itself was 73.2 centimeters (28.8 in) in diameter.

Small probes

File:Smallvenusprobe.gif

A small probe (1-antenna, 2-temperature sensor, 3-frontal protection, 4-hermetic container, 5-nephelometer, 6-radiometer)

Three identical small probes, around 0.8 metres (2 ft 7 in) in diameter, were deployed. These probes consisted of spherical pressure vessels surrounded by an aeroshell, but unlike the large probe, they had no parachutes and the aeroshells did not separate from the probes.

Each probe carried a nephelometer and temperature, pressure, and acceleration sensors, as well as a net flux radiometer experiment to map the distribution of sources and sinks of radiative energy in the atmosphere. The radio signals from all four probes were also used to characterize the winds, turbulence, and propagation in the atmosphere.

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.

Launch

The Pioneer Venus Multiprobe was launched by an Atlas SLV-3D Centaur-D1AR rocket, which flew from Launch Complex 36A at the Cape Canaveral Air Force Station. The launch occurred at 07:33 on August 8, 1978, and deployed the Multiprobe into heliocentric orbit for its coast to Venus.

Arrival at Venus

Prior to the Multiprobe reaching Venus, the four probes were deployed from the main bus. The large probe was released on November 16, 1978, and the three small probes on November 20.

All four probes and the bus reached Venus on December 9, 1978. The large probe was the first to enter the atmosphere, at 18:45:32 UTC, followed over the next 11 minutes by the other three probes. The bus entered the atmosphere at 20:21:52 UTC, and returned its last signal at 20:22:55 from an altitude of 110 kilometres (68 mi).

The four probes transmitted data until they impacted the surface of Venus. The Day Probe survived impact, returning data from the surface for over an hour.

Pioneer Venus probes and bus: atmospheric entry and impacts (all times in UT)

	Large Probe	North Probe	Day Probe	Night Probe	Bus
Entry time (200 km)	18:45:32	18:49:40	18:52:18	18:56:13	20:21:52
Impact time	19:39:53	19:42:40	19:47:59	19:52:05	(signal lost at 110 km altitude)
Loss of signal	19:39:53	19:42:40	20:55:34	19:52:07	20:22:55
Impact coordinates					(estimated)
Solar Zenith Angle	65.7	108.0	79.9	150.7	60.7
Local Venus time	7:38	3:35	6:46	0:07	8:30

See also

• Timeline of artificial satellites and space probes

External links

• NASA: Pioneer Venus Project Information
• Pioneer Venus Program Page by NASA's Solar System Exploration
• NSSDC Master Catalog: Spacecraft Pioneer Venus Probe Bus. (Other components of the mission have their own pages at this site too.)
• Several articles in Science (1979), 205, pages 41-121