The Probe | The Spacecraft | Key Features

The Galileo Project promises to become one of the most challenging and exciting projects of the next decade. It has been chosen by NASA, the science community, and the Congress as another logical step in the orderly exploration of the solar system. Conceptual studies have shown that it is feasible. Now comes the demanding task of developing and testing the flight hardware in time to match the 1981 to 1982 launch opportunity. Then a long period of suspense follows, after which Jupiter and its satellites will start to yield up their secrets.

...Its appeal lies rather in the stimulation and thrill of exploration it provides; a sense of participation that permeates the whole organization, not just the lucky few who are directly involved. The technical challenges also play a part by testing and developing the ingenuity and problem-solving capability of our people. Finally, the program offers both companies [Hughes/General Electric] another opportunity to demonstrate peaceful uses of space technology to help answer the great scientific questions of our time.

A.D. Wheelon
Vice President and Group Executive
Space and Communications Group
Hughes Aircraft Company

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.

The probe mission is likely to end when the main Galileo spacecraft passes beyond radio contact with the probe as the spacecraft enters Jupiter orbit. The ultimate fate of the probe may be first determined by its battery lifetime or it may succumb to the immense pressure of Jupiter's atmosphere or ever increasing temperature. The Galileo spacecraft, meanwhile, will begin two years of close up studies of Jupiter and its satellites.

Galileo Program Manager Bernie Dagarin remembers well the moment on Oct. 18, 1989, that the Space Shuttle Atlantis carrying the Galileo spacecraft in its hold was launched. At 9:54 a.m. Pacific Daylight Time, Galileo was lifted through a patch-work of puffy, white cumulus clouds towards Jupiter.

That day was the culmination of an eleven year effort by initially more than 100 Hughes engineers and scientists who overcame a host of technical and budgetary challenges to meet the unique requirements of designing and building a space probe that would survive immense entry heating, high deceleration forces (425 Gs), atmospheric pressure, and ever increasing temperatures.

"The packaging density within the units, and the units within the probe were things that we never encountered before, " said Dagarin, who had been a member of Hughes' Pioneer Venus and Surveyor teams before joining the Galileo team as Power Systems Engineer. "Volumetric constraints were a real challenge throughout the program," he said.

Dagarin, who is just the third person to direct the Galileo program for Hughes, succeeded John Radecki after the launch of the spacecraft in 1989. Uldis Lapins served as program manager for Galileo from 1976 to 1986.

Although several volumes of documentation on the development, testing, and operation of the probe exist, Dagarin said if given the opportunity again, he would insist on more detailed documentation of all design decisions and test results in order to assist the next generation in why things were done in a particular way. "As for testing, the probe was subjected to far more tests than normal satellites," Dagarin said. Everything had to be subjected to pressure/temperature tests simulating atmospheric descent and centrifuge testing to simulate the entry deceleration forces. Simulation drop tests, using a helium balloon and gondola, were made from 95,257 feet to test the deployment of the parachute and separation systems. And, of course, each unit was tested exhaustively on the bench and under all of the environments.

The heat shield design of the probe, a collaborative effort between General Electric, Hughes, and NASA's Ames and Langley Research Centers, had to be conservative in order to survive the enormous heat load during entry. The descent module aerodynamic design was a collaborative effort between HSC and Missile Systems Group with model testing in ARC wind tunnels.

Dagarin said the program was blessed by having exceptional people. He gives his permanent staff of four high praise and when additional help is needed he said he finds that other people in the company seem to find the time to lend a hand, especially former Galileo team members.

Dagarin is not the only one to give the team high marks for their performance on Galileo. Pat Melia, NASA's Ames Research Center, probe engineering team chief at JPL, said "The team did an outstanding job to get ready for the release." "There is a uniqueness about this program, unlike other space efforts that generates a high level of esprit de corps among its participants. Even after shut downs in the program, one taking up all of 1980, the esprit de corps among our people remained high," Dagarin said.

Dagarin's full-time staff members are Jean Sobolik, Dick Sakal, Dan Carlock, and Fred Linkchorst.

Sobolik has been in charge of the data bank for the Galileo program for the last eight years. Every program she has had the good fortune to work on in her 23 years at HSC has been a success she says. She said she has enjoyed working with all of the people associated with the program and is looking forward to another successful event Dec. 7.

Sakal joined the Galileo team in 1987 as its test director. His job was to supervise all of the electrical systems testing. Today, he is responsible for flight operations of the Probe and Radio Relay hardware (on the orbiter) and the probe ground data processing systems. He said, " the most interesting aspect of the program is that it has never been done before." Systems Engineer, Fred Linkchorst is most impressed by the level of planning that has gone into the program and how smoothly everything has gone. "It is nice to know that something that was built so long ago worked so well-as advertised," Linkchorst said. Linkchorst came to the program after working on shuttle Ku-Band and Magellan programs at HSC.

"I hope people will take a few moments to reflect upon this project," Carlock said. "A lot of senior people at Hughes Electronics cut their teeth on this program. Many have done a remarkable job of responding to customers' needs under trying circumstances such as the failure of the high gain antenna and the subsequent attempts to free that antenna, which exposed the probe to solar heating during the thermal turns ,and of course the launch delays. Inspite of these and other challenges, the probe's release was flawless.

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It's Galileo, By Jupiter

click on spacecraft to see large line drawing (48k)

Almost 400 years ago, Italian scientist Galileo Galilei looked through his telescope at the planet Jupiter and "perceived that beside the planet there were three starlets, small indeed, but very bright.." Eventually, Galileo would discover a total of four moons, unknown before the invention of the telescope, orbiting around Jupiter-a discovery that would eventually change how humanity viewed the heavens.

The interplanetary explorer Galileo will conduct nineteen investigations using the spacecraft's radio system and many different scientific instruments (six of which will drop into Jupiter's atmosphere on the probe). Galileo will orbit on the Jovian system for two years, gathering data and taking pictures that can detect objects as small as 12 meters (39 feet).

The Jet Propulsion Laboratory designed and developed the Galileo Jupiter orbiter spacecraft and is operating the mission; NASA's Ames Research Center developed the atmospheric probe with Hughes Space and Communications Company as prime contractor. The German government is a partner in the mission through its provision of the spacecraft propulsion subsystem and two science experiments on the probe.

Like Voyager and other previous interplanetary missions, Galileo used planetary gravitational fields as auxiliary propulsion stages. The spacecraft dipped into the gravitational fields of Venus and Earth to pick up enough velocity to get to Jupiter. This 38-month Venus-Earth-Earth Gravity Assist phase ended with the second Earth flyby on December 8, 1992. It provided, in addition to the velocity increment, opportunities for useful scientific observations and an exercise of the spacecraft's scientific capabilities.

Galileo's two planned visits to the asteroid belt provided the first and second opportunities for close observation of these bodies: in October 1991 the spacecraft flew by asteroid Gaspra, obtaining the world's first close-up asteroid images; in August 1993, it flew by a second asteroid, Ida, and discovered the first confirmed asteroid moon.

In late July 1994, Galileo was the only observer in a position to obtain images of the far side of Jupiter when more than 20 fragments of Comet Shoemaker-Levy plunged into the night-side atmosphere over a 6-day period.

In December 1995, the Galileo atmospheric probe will conduct a direct examination of Jupiter's atmosphere, while the larger part of the craft, the orbiter, begins a 23-month, 11-orbit tour of the magnetosphere and the Galilean moons, including ten close satellite encounters.

Galileo's orbital science results will be transmitted to Earth over the low-gain antenna at significantly lower data rates than originally planned, because of the in-flight failure of the high-gain antenna to deploy as commanded in April 1991. The project team has developed means to transmit the key scientific data and to accomplish most of the project's Jupiter science objectives, using on-board data processing and compression, and various enhancements to the communications link performance, including new encoding systems and advanced technology in ground equipment.

The 2-1/2 ton Galileo orbiter spacecraft carries 10 scientific instruments: there are another six on the 750-pound probe. The spacecraft radio link to Earth and the probe-to-orbiter radio link provide data for additional scientific investigations. Galileo communicates with its controllers and scientists through the Deep Space Network, using tracking stations in California, Spain, and Australia.

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