Pioneer Venus
Pioneer Venus Orbiter (foreground) and multiprobe.
Eight-Month Mission Lasts Fourteen Years
The Pioneer Venus orbiter, the remaining component of the Pioneer Venus mission, entered the upper atmosphere of Earth's sister planet in September 1992. The slow descent brought the demise of the hardy orbiter in October 1992. By the end of its life, the orbiter had uncovered and transmitted trillions of bits of information during its 14-year obsession with Earth's closest planetary neighbor.
- Hughes Aircraft Company, later Hughes Space and Communications Company of Los Angeles, and now Boeing Satellite Systems, Inc., designed and built both the spacecraft and the science probes used for this unique mission.
- The mission, slated to last one Venusian year (243 days), ran 14 years.
- Hughes delivered the spacecraft on the exact date set four years previously. The launch windows were fixed because of the precise juxtaposition of Earth and Venus. If the launch dates had not been met, the mission would not have been accomplished. The orbiter was launched on an Atlas Centaur May 20, 1978. The multiprobe vehicle followed August 8, also on an Atlas Centaur. The two spacecraft arrived at Venus within 4 days of each other in December of that year.
- The single multiprobe spacecraft was the first in history to divide into five independent vehicles. Hughes scientists and engineers developed the innovative spacecraft consisting of a probe carrier or bus, a large probe, and three small probes. The five spacecraft contained 18 scientific instruments.
- To survive the free-fall through the dense, corrosive Venusian atmosphere, Hughes encased the scientific instruments in titanium spheres aboard the probes. Casting and machining the titanium hemispheres to the critical tolerances required more than nine months each. "The project was like sculpting in titanium," one Hughes engineer recalls.
- Hughes engineers overcame the challenges of devising a lightweight structure, harness, windows, seals, electrical feedthroughs, a parachute, and other probe elements to withstand intense heat, corrosion, a 565-g entry force, and pressure nearly 100 times that of Earth (the pressure of an ocean at 3000 feet).
- Responding to the unusual requirements of the probe seals (8 seals per small probe and 15 for the large probe), Hughes invented a special sealant material called Grafoil. The seals contained the xenon gas in the probes during their four months' travel in the vacuum of space, then withstood the bone-crushing pressures (100 atmospheres) during entry into the planet's lower atmosphere.
- The windows in the probes, through which the scientific instruments viewed the Venusian atmosphere, presented a special challenge to Hughes; no glass or plastic could endure the corrosive, high-temperature environment. Sapphire was chosen for all windows except one, which had to admit infrared rays.
- A large natural diamond was used for the remaining window. After a year-long search for two suitable diamonds (one for the window and one for a spare), the diamonds (200 carats and 30 carats) were processed into two windows, each the size of two stacked pennies.
- To control costs, Hughes incorporated existing technology, designs, and hardware in every instance possible. The orbiter design evolved from previous Hughes spacecraft and satellites. The radar mapping system was based on Hughes' advanced military radar systems, and the communication system was a modification of systems already proven in Hughes communications satellites and interplanetary exploration spacecraft.
- Use of common hardware was another method of controlling costs. The commonality achieved between the orbiter and the multiprobe bus was 78 percent. This commonality substantially reduced the amount of hardware that had to be developed.
- The Hughes team also developed a parachute system that deployed successfully at velocities near the speed of sound and slowed the large probe in a sulfuric acid vapor environment.
- All probes operated perfectly, transmitting data throughout their hour-long descent. One of the smaller probes survived impact and continued to transmit valuable data from the planet's surface for 67 minutes before it succumbed to the extreme heat. The probes provided more information about Venus than all the of the data collected by astronomers about the mysterious planet in the past 500 years.
- The orbiter was the first spacecraft to provide extensive radar mapping of Venus.
- Scientists have sent the orbiter more than two million commands and have received more than ten trillion bits of data.
- Among the noteworthy discoveries of the orbiter is the high-altitude haze layer that envelops Venus' clouds and appears and disappears over a period of several years.
- By studying the data transmitted by the orbiter, scientists have uncovered possible implications of Earth's future. Venus, now devoid of water, had oceans 3.5 million to 4 million years ago. Solar ultraviolet rays separated the hydrogen and oxygen. The hydrogen blew into space, and the oxygen combined with carbon to form carbon dioxide gas.
Artist's conception of Pioneer Venus orbiter entering Venus' atmosphere.
- Due to its greatly extended mission life, the orbiter was able to capitalize on unexpected opportunities, particularly in the observation of comets as they approach the sun. The U.S. did not plan a mission to investigate Halley's Comet upon its approach in 1986. However, scientists realized that the hardy Pioneer Venus orbiter could be pressed into service due to its fortuitous location. Scientists commanded the orbiter to flip over, observe, and transmit data during the entire cycle of Halley's Comet.
- The mission, called the most complex and innovative unmanned space venture ever undertaken, led the way for such subsequent long-term planetary expeditions as the Magellan mission to Venus, for which Hughes built the radar mapper, and the Galileo mission to Jupiter, for which Hughes built a similar scientific probe system.
- The Magellan mission, launched May 4, 1989, capitalize on the surface mapping gleaned by both the Pioneer Venus orbiter and its companion multiprobe spacecraft. While the Pioneer mission provided the first mapping of the surface, Magellan's prime concerns were more extensive mapping of Venus' surface and observation of changes.
- Galileo, launched October 18, 1989, completed a six-year journey to Jupiter. The Galileo probe was the same size as the large Pioneer Venus probe. Hughes scientists used a similar two-section design on both spacecraft. Like Pioneer's probes, Galileo's instrument-laden descent module was also built by Hughes. The probe's brief travel through Jupiter's atmosphere (approximately 75 minutes) generated more information about its target planet than all other space missions gone before.
Hughes creatively combines its existing technology with its continuous innovations to unveil the mysteries of our universe as well as our home planet.
In October 2000, The Boeing Company acquired three units within Hughes Electronics Corporation: Hughes Space and Communications Company, Hughes Electron Dynamics, and Spectrolab, Inc., in addition to Hughes Electronics' interest in HRL, the company's primary research laboratory. The four are now part of Boeing's newest subsidiary, Boeing Satellite Systems, Inc.
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