Galileo Probe's Guardian Angel

DN Staff

March 3, 1997

25 Min Read
Galileo Probe's Guardian Angel

El Segundo, CA--If you're a typical design engineer, you complete a dozen or more projects a year. But what would you do if you had but one unique, high-risk project that would test your technical skills and personal fortitude for the better part of two decades? And what if the product you labored so hard to design and test over all those years literally began disintegrating just one hour after it started operating?

That, in brief, was what Bernard Dagarin experienced on the Galileo space probe project.

Of course, the veteran engineer had no idea what lay before him in 1978 when Hughes Space and Communications Company won the contract from NASA Ames to design and build a probe that would plunge into the hellish atmosphere of Jupiter to capture priceless scientific data.

But in the years leading up to that dramatic encounter of the Galileo probe with the giant outer planet on Dec. 7, 1995, Dagarin would see his role escalate dramatically. From his first assignments on the battery and power subsystems, Dagarin would eventually become the man who guided the program through some of the toughest trials ever to face an engineering team.

"The project was an enormous achievement for the space program and a very big triumph for our company," says Mal Meredith, a former top engineering manager at Hughes, "and it was Bernie's sheer tenacity that kept it going. Anyone else would have given up two or three times along the way."

Adds Hughes Space and Communications Co. Vice President Mike Gianelli: "I owe him a personal and professional debt of gratitude for all his years of dedication. He was the glue that held the program together."

The tension mounts. Right up to the Dec. 7 afternoon when engineers and scientists huddled together at the Jet Propulsion Lab (JPL) operations room to await the first signals from the probe as it entered the Jovian atmosphere, no one knew for sure if all those years of hard work would pay off.

"There were so many variables that we had to address," recalls Probe Systems Engineer Doug Anders, "and there were nagging doubts about whether we had turned over every stone."

After all, the engineers had asked the 747-pound probe, measuring 49 inches in diameter and 34 inches in height, to withstand some incredible conditions since it first blasted into space on Oct. 18, 1989, aboard the Space Shuttle Atlantis. Housed within the Galileo Orbiter, which the astronauts ejected from Atlantis two hours after launch, the probe would need to lie dormant--except for periodic systems checks--for more than six years. During that time, the Galileo Orbiter would have to travel through space nearly 2.4 billion miles before releasing the probe in July of 1995 to begin its final 50-million-mile journey into Jupiter's inferno.

Never before had a spacecraft been asked to survive such a long and difficult mission. When it was time to "perform" during the actual planetary encounter, would something go wrong and spoil the whole show?

The questions were endless. As the probe ripped through Jupiter's upper atmosphere at 106,000 mph, would its heat shield withstand temperatures twice that of the surface of the Sun (15,500C), and would its structure hold up under gravitational forces 230 times that of Earth? Could it really survive the highest impact speed of any man-made object ever--50 times faster than a bullet fired from a high-powered rifle?

Would its thermal batteries perform as planned and trigger the mortars that would separate the probe's outer shell, called the deceleration module, from the 278-lb inner descent module containing the six scientific instruments? Would the main parachute deploy properly and allow the module to sink as planned through 125 miles of Jupiter's atmosphere at 110 mph? Would the innovative lithium/sulfur dioxide batteries provide reliable power to the all-important scientific instruments? And would the radio relay receiver aboard the orbiter--flying 125,000 miles overhead--acquire and track the precious signals from the probe, the long-awaited data that scientists hoped would bring fresh insights into the origins of the solar system?

The answer to these and many more anxious questions was a resounding "yes."

"We didn't know whether to laugh or cry," says Dagarin, recalling the "electric" atmosphere in JPL's operations room that Dec. 7. "Some of us did both."

Pleasant surprises. The joy that the engineers felt when the Hughes' relay receivers on the orbiter first locked onto the probe's signals multiplied as the minutes ticked by. All the scientific instruments performed as planned, feeding data to the orbiter for 58 minutes. Not only that, but the signals continued far deeper into Jupiter's atmosphere than mission planners had anticipated--to a level where atmospheric pressures were 24 times that of the Earth at sea level. Result: Scientists got even richer data than anticipated.

"The probe was a fabulous success," says William O'Neil, Galileo project manager at JPL. "It did a superb job of fulfilling the objectives of one of the most important space missions of the last several decades."

Sixty-one minutes after it first entered Jupiter's upper atmosphere, the probe's mission ended. Radio signals ceased, and the probe, bit by bit, began to melt under the planet's increasingly intense heat--first the Dacron parachute, then the aluminum and titanium structure. At the 5,000-bar level, the probe had become nothing but vapor.

A simple chart plotting the probe's ultimate demise as it sank deeper into the hot gases of Jupiter is taped to the wall behind Bernie Dagarin's desk in a windowless office of building S-50, part of the sprawling Hughes complex near the Los Angeles airport. To cynics, the chart might represent a cruel statement about the fleeting nature of a product to which Dagarin devoted the prime of his engineering career. But if you talk to Dagarin and his team, you begin to understand the real value of the project.

Yes, the Galileo probe, by all accounts, was a technical and scientific triumph, yielding vital data that researchers will analyze for many years to come. But every bit as important was the engineering quest that preceded it--a quest that challenged Dagarin and his colleagues to solve countless design challenges that no engineering team had ever solved before. Moreover, they had to tackle these problems in the face of agonizing setbacks.

The legacy of Pioneer Venus. But Dagarin could never have envisioned the long and tortuous path ahead when he first joined the new Galileo probe team in August of 1978. After all, he had just completed a very satisfying six-year stint on the Pioneer Venus project, for which Hughes built both the orbiter and a multiprobe vehicle. And earlier in his Hughes career, he had worked for several years on the series of Surveyor spacecraft, which made soft landings on the moon to gather lunar data in preparation for the manned Apollo missions.

The Pioneer Venus mission, which introduced many technologies that would later be used on the Galileo probe, featured a multiprobe vehicle that successfully deployed a large probe and three small ones. Together, the probes carried 18 scientific instruments. The mission posed all sorts of technical challenges. For example:

To survive the free fall through the dense, corrosive Venusian atmosphere, the scientific instruments were encased in titanium spheres, each of which took nine months to machine.

  • Engineers invented a special sealant to prevent leakage of precharged gas from the probes, as well as to keep out Venusian gases at pressures nearly 100 times that of Earth.

  • Because of intense heat that would melt ordinary glass windows, the probe's windows had to be fashioned from sapphire and even diamond, in the case of one window that had to admit infrared rays.

Electrical harnesses--a Dagarin specialty--offered many challenges. Not only did he have to design them to fit within the extremely compact dimensions of the probes, but they had to survive 560-g forces upon entry and temperatures reaching 900F. A broken harness or one that ripped out of a connector could silence the very instruments that were the reason for the whole project.

In addition, Dagarin played a major role in integrating and testing the silver-zinc battery system that powered the probes. He also bore major responsibility for the pyrotechnic and electromechanical devices that separated the probes from the multiprobe bus.

Throughout all these projects, Bernie earned a reputation for painstaking attention to detail and a willingness to pursue and address every conceivable problem.

"He was always his own toughest task master, doing test after test," recalls Meredith, who was Hughes' associate program manager on Pioneer Venus. "Bernie worried about what people might call the 'dirty' parts of systems engineering--things like electrical systems, which others might consider mundane but that can scuttle a whole mission if they aren't right."

"The mission was a spectacular technical success," notes Steven Dorfman, former program manager on the project and now chairman of Hughes Telecommunications and Space Co. Scientists say they learned more about Venus from the probe's 90-minute encounter with the planet than had been learned in the five centuries since Galileo.

A new challenge. Equipped with the knowledge and technology gained from the Pioneer Venus experience, Dagarin and his Hughes colleagues enthusiastically tackled the company's second major probe contract with NASA--the Galileo probe. Its scientific goals were indeed tantalizing. Among them:

Determine the temperature and pressure of the Jovian atmosphere, as well as the planet's chemical composition and cloud structure.

  • Measure radiation levels, the helium to hydrogen ratio, and the velocity and depths of Jupiter's winds.

  • Check the occurrence and energy of lightning and characterize high-energy particles near Jupiter.

From an engineering standpoint, the project was clearly a plum: The spacecraft would be the first to enter the atmosphere of any of the four outer giant gas planets beyond Mars. The great distance involved and the extended time in flight demanded lighter and more durable systems. Unlike the Pioneer Venus probe, which used a sealed pressure vessel to withstand Venus's 100-bar-pressure environment, the Galileo probe saved weight by being vented to Jupiter's atmosphere.

Moreover, the craft would have to survive the violent extremes of speed, temperature, gravitational forces, and pressure. For example, in the space of four minutes, the probe would slow from 106,000 mph (fast enough to cross the U.S. in 85 seconds) to 250 mph.

"The Pioneer Venus was a very difficult challenge," says Dorfman, "but the Galileo probe was even tougher."

Dagarin, however, wasn't intimidated. "I jumped at the chance to be a part of it."

If he only knew how hard it would be. Originally, mission planners hoped to have the orbiter and probe ready for launch as early as 1982. Rather than the seven-month journey of the earlier probe to its encounter with Venus, they estimated it would take the Galileo probe two and a half years before it reached Jupiter--some 350 million miles beyond Earth's orbit.

But that scenario proved far too optimistic. Again and again, the launch date was pushed back. Engineers at Hughes and its subcontractors--most notably GE's Re-entry Systems Div.--had to design the outer deceleration module and the inner descent module that housed the scientific instruments. Then they had to work with JPL to integrate the probe with the orbiter, as well as develop operation procedures for the mission. Testing also presented more challenges. Engineers subjected the probe and its components to myriad tests--wind tunnels, centrifuges, vibration, thermal-vacuum, as well as high-speed arc-jet and laser tests for the heat shield.

Yet they knew full well that these procedures couldn't truly simulate the hostile environment that the Galileo probe would face in space, such as the 15,500C temperature at initial entry. The forward heat shield, made of a carbon phenolic material, would not only have to withstand this enormous amount of radiated heat but also the sheer mechanical erosion as the spacecraft slammed into the atmosphere. Physical tests, obviously, fell short of mimicking this environment, so engineers had to rely on large and complex computer codes to insure that the design would be robust enough. Even so, they provided for a 30 to 44% safety margin in the shield's thickness, reaching a maximum six inches at the nose.

"We tested all that we could, but there were times when we had to make an analytical leap of faith," notes Dagarin.

Other delays resulted from changes in launch-vehicle configuration. Galileo was designed as the first American planetary mission to be launched from the space shuttle. So engineers needed to complete a design that called for attaching the orbiter and probe to the top of a modified Centaur rocket--the same hydrogen-fueled upper stage used for previous planetary missions, such as the Surveyor, Viking, Pioneer, and Voyager launches.

This time, however, instead of being mounted on a larger, first-stage rocket booster, the entire orbiter-probe-Centaur combination would be loaded into the shuttle's cargo bay. Once the shuttle reached Earth orbit, the astronauts would open the cargo door and deploy the rocket and its cargo.

A devastating loss. By the fall of 1985, the engineers felt they had licked all the problems. In December, NASA shipped both the orbiter and the probe to Florida's Kennedy Space Center in preparation for a scheduled May 1986 launch. Then, the unthinkable happened. On January 28, the Space Shuttle Challenger exploded shortly after launch, killing all seven astronauts, including Greg Jarvis, a civilian payload specialist from Hughes.

"First we had to get through the great personal loss of losing Greg, who was our friend and colleague," remembers Systems Engineer Doug Anders. "Then, we had to face the fact that it would be a long, long time before we could ever launch Galileo."

After the Challenger was lost, for example, the NASA safety review board ruled that it would be too dangerous for the shuttle to carry the Centaur upper stage, with its liquid rocket fuel.

That policy would have dramatic consequences for the Galileo mission. The probe would still be launched from the shuttle, but only with a lower-thrust, solid-rocket upper stage. What's more, rather than the direct flight to Jupiter as originally planned, the new launch mode would require that Galileo receive gravity-assist kicks from two orbits around the Earth and one orbit around Venus. Result: Instead of a 21/2 year mission, it would now take the probe more than 6 years to reach Jupiter.

These events profoundly affected everything and everybody associated with the program. "There was shock, followed by malaise. People just didn't know what to do," remembers Dagarin.

Rising to the occasion. Fortunately, for Hughes, there was a Bernie Dagarin. Within days of the Challenger disaster, Dagarin began to see that every component and every system within the probe would have to be re-evaluated in the light of this new lengthy timetable. Accordingly, working with the primary vendor companies, he and his colleagues began a long and painstaking series of shelf-life analyses and tests to determine which parts of the probe would have to be replaced or redesigned. Among the items replaced: the Dacron parachutes, the mortar cartridges that deploy the parachute, and the lithium/sulfur dioxide batteries so crucial to the science mission.

The tripling of the transit duration was a real concern to the battery engineers. So Dagarin called on experts at the Sandia National Laboratories to perform life-assessment tests on the lithium/sulfur dioxide batteries. That work, which also produced new glass battery seals to protect against corrosion, determined that there would be a worse-case loss of no more than a 0.04% A-hr per module per year loss, assuming a 6-year temperature of 0C during flight. Dagarin also worked very closely with the Philadelphia-area battery vendor Honeywell Power Sources (now Alliant Techsystems) on battery manufacturing and testing.

Providing the main power source for the mission, the battery system would comprise three lithium/sulfur dioxide battery modules, each containing 13 D-sized cell strings. The modules would have to retain their capacity for 7.5 years and support a 150-day clock, ending with a 7-hour mission sequence of increasing loads from 0.15A to 9.5A during the last 30 minutes.

"Bernie made many, many trips to our plant," notes Becky Smith, who was the program manager for battery supplier Honeywell, "and he got to know everyone who worked on the project, which over time was more than 50 people. He made sure that we all knew how important our technology was to the whole program."

In the end, the batteries performed flawlessly. A similar system will power the European Space Agency's Huygens probe, scheduled for an encounter with Titan in the year 2004.

But batteries weren't his only concern. As the years after Challenger wore on, Dagarin--more than any other engineer in the program--took it upon himself to reverify the design and reliability of every component and system within the probe. His thoroughness became legendary.

"Nothing slips by Bernie. He's the most detail-oriented engineer I know," says Fred Linkchorst, a systems engineer on the probe. One example was the very remote chance of a short occurring in the orbiter and interrupting the bus supplying power to the probe during the critical orbiter-probe separation sequence. Such an event could prematurely activate the probe battery system--as if it had just arrived at Jupiter. Still, the short would only be a problem if it occurred during a 4-second interval in the latter stages of separation. "Bernie attacked the problem with a vengeance, with all sorts of tests, charts, and contingency plans," remembers Linkchorst.

That kind of care and diligence caught the attention of Hughes' customer, NASA Ames, which was responsible for the probe (JPL developed the Galileo orbiter and oversaw the entire mission). "It was a real treat working with Bernie," notes Marcie Smith, Galileo probe project manager at Ames. "He not only had a thorough knowledge of the spacecraft but of the entire mission."

The mentoring art.Dagarin also encouraged every member of the Hughes probe team to take this same broad view--especially younger engineers who were getting their first experience as systems engineers. Rather than impose his will, he invited their ideas and challenged them to take on wider responsibilities. For example, engineer Peggy Nugent, who started on the program as a power supply designer, recalls being "intimidated" by systems engineering. But before she left the program, Bernie had not only moved her into systems work but had put her in charge of the design review board for the entire probe.

"Bernie loved Galileo and communicated that love and commitment to all of us," says Nugent.

He also conveyed to them the overwhelming importance of taking the long view on design projects, of anticipating every problem and finding solutions. All of which, these designers say, made them better engineers.

The strong relationships and team spirit that Dagarin forged with his engineering colleagues would be vital as the programmed dragged on. Time and again in the years after the Challenger disaster, when the Hughes probe team shrank to a skeleton crew, Dagarin sought assistance from engineers who had retired from the company or had been reassigned to other programs. Invariably, they would come back to troubleshoot for him, often working without pay on nights or weekends.

"He was in a very difficult position," says Ed Limberg, who did much of the early design work on the probe's innovative data and command processor. "Many of us who designed the original hardware had gone on to other assignments. So when Bernie called and asked us for help, how could we say no? We really wanted to help him."

Up from the ranks. In large part, everyone from fellow engineers to vendors was willing to help Dagarin because they viewed him as one of their own. No prima donna here--just a dedicated, hardworking engineer scratching and clawing for solutions to more problems than he himself could ever solve on his own.

His engineering training had come mostly the hard way--on the job. The son of a Yugoslavian immigrant who worked as a glass worker and part-time farmer in western Pennsylvania, Dagarin learned early how to work with tools. He got his first real taste of engineering from Army guided- missile training during the Korean War. After the service, he joined Chrysler's missile division, working closely with the Huntsville, Alabama-based Army Ballistic Missile Agency, which later became Marshall Space Flight Center. While he worked, he took college engineering courses at both the Chrysler Institute of Technology in Detroit and the University of Alabama.

Then came assignments to install and maintain guided-missile installations in Italy and Turkey--"all of them pointed at Russia." The job taught him a lot about a whole range of disciplines that would later be very important to his career--mechanics, propulsion, materials, and electrical systems. Along the way, he developed solid relationships with applications engineers at vendor companies. Says Dagarin: "They were invaluable to me. I learned so much from them."

In the unpredictable world of engineering, this ability to tap into expertise from anywhere and everywhere can't be overestimated. Even after the long-awaited successful launch of Galileo aboard the Space Shuttle Atlantis on October 18, 1989, the technical surprises continued for Dagarin, who by then had been named the Hughes program manager.

In April of 1991, for example, mission operations discovered that the Galileo orbiter's 16-foot-wide, high-gain antenna could only be partially opened. This was a big setback, since the umbrella-like antenna was to play the principal role in relaying scientific data from Jupiter to Earth. For many months, engineers at JPL studied the problem and attempted various fixes. They tried to force it open with its motors. And they tried heating the antenna using sunlight, then cooling it by turning the orbiter toward the cold darkness of space. Nothing worked; the antenna remained stuck.

All the while, of course, Dagarin and his team fretted about the effect of these maneuvers on the probe's components and scientific instruments. This triggered a whole new round of ground tests and contingency plans--including a half million dollars' worth of new thermal studies ordered by Dagarin. What's more, the mission would now have to rely on the orbiter's low-gain antenna for data transmission, which would severely limit Dagarin's ability to do system checks of the probe systems during flight. Engineers scrambled to develop new software code and data-compression methods to insure the mission's success.

Nail biter. With such snafus, it is no wonder that the Hughes probe team--now operating out of JPL in the final years of the mission--was so anxious when the probe separated from the orbiter on July 12, 1995, to begin the final 50-million-mile journey to Jupiter. For five months, mission operations would not be able to contact the probe or change its trajectory. Unless the probe entered the Jovian atmosphere at the precise flight-path angle, it would either skip off into deep space or be reduced to ashes. All the engineers and scientists could do was wait for encounter day, when an on-board timer would "wake up" the probe and activate the batteries to power the final exploratory descent to Jupiter.

During that tense vigil before the encounter, Bernie took his engineers aside and prepared a "doomsday list" of all the things that could go wrong--"just in case we needed them to tell the press."

As it turned out, no excuses were needed. There were just two mission anomalies of any real consequence: the parachute opened about a minute late, and the probe's thermal protection could not provide full protection from the tremendous temperature extremes. Even so, all the instruments worked, relaying the long-coveted data for nearly an hour.

"People are very excited about what the probe mission told us about Jupiter," says Marcie Smith of Ames. "Scientists will be analyzing this data for many years to come."

For Hughes, the triumphant mission was like a giant billboard testifying to the quality of the company's technology and engineers. Even for a firm famous for its sophisticated communications satellites and defense systems, the Galileo probe mission was something very special. The value of the contract itself--$172 million--paled by comparison to the great sense of pride it instilled in Hughes engineers. "For Bernie and the engineers who supported him, it was the high point of their careers," says Hughes Vice President Gianelli.

But what if the mission had failed, as Russia's $300 million Mars '96 probe did last November, bringing a devastating blow to that nation's space program? "I don't think I could have handled that," admits Dagarin, as he looks back on nearly 20 years of hard work and countless problems encountered and solved. "Except for the birth of my children, I've never felt a greater thrill than the moment when we got that first signal from the probe."

Jupiter: a mysterious giant

Why the fascination with Jupiter? Scientists believe the cloud-shrouded atmosphere of the largest planet in the solar system holds the key to the universe's secrets.

Containing more mass than all the other planets combined, Jupiter is in orbit 500 million miles from the Sun and 350 million miles from Earth. Not just a single planet, it is the central object of a complex system involving four large moons, at least 12 smaller satellites, a ring system, and a powerful magnetic field. Besides the important probe en-counter that occurred on Dec. 7, 1995, the Galileo mission is sending the orbiter on a "grand tour" of Jupi-ter's system, including several orbits of its prime satellites during whichit will return high-resolution images and gather key atmospheric data.

Composed primarily of hydrogen and helium, the same elements common to the stars and the sun, Jupiter is a planet of liquified light gases with a rocky core that could contain as much material as 10 Earths.

Theories of the origin of the solar system rest on the assumption that all celestial bodies formed from a gaseous material of uniform composition. As they cooled and contracted, the makeup of planets changed. But while the terrestrial planets lost most of their light elements, the gravitational fields of Jupiter and the larger outer planets retained theirs.

The probe encounter and the planetary tour are vital, scientists say, because Jupiter, of all the planets, most closely represents the primordal solar nebular material, making it the ideal cosmological laboratory.

Unlocking Jupiter's secrets

It will take many years for scientists to fully evaluate all the data from the Galileo probe's encounter with Jupiter. But the first evidence from the probe's exploratory instruments reveals some interesting new insights. Among them:

The Energetic Particle Instrument, which measured radiation in the inner regions of Jupiter's magneto-sphere, discovered an intense radiation belt between Jupiter's ring and uppermost atmospheric layers. The radiation is about 10 times stronger than the Earth's Van Allen radiation belts and includes high-energy helium ions of unknown origin.

  • As the probe plunged into Jupiter's atmosphere, the Atmospheric Structure Instrument found that upper atmospheric densities and temperatures were significantly higher than expected, while the deep atmosphere proved to be drier and convective. Scientists look to the probe data to better understand the influence of internal heat pouring forth from Jupiter's core.

  • To scientists' surprise, the Nephelometer found only small concentrations of cloud and haze materials--though mission specialists theorize that this could be due to the probe's entry in an unusually clear region.

  • Measuring the vertical variation of winds, the Doppler Wind Experiment detected fierce winds as high as 450 mph deep in the Jovian atmosphere, suggesting the intense heat radiated from the planet's interior.

  • Initial results from the Neutral Mass Spectrometer in-dicate that Jupiter's at-mosphere has much less oxy-gen--mainly found as water vapor--than the Sun's atmosphere, implying a surprisingly dry atmosphere. Little evidence of organic molecules was found.

  • The Lightning and Radio Emission Detector found that the lightning activity is 3-10 times less common than on Earth, though lightning bolts are much stronger. Since lightning is believed to produce organic compounds, these findings support the dearth of such molecules, as seen from the Neutral Mass Spectrometer readings.

  • The Helium Abundance Detector very accurately measured the abundance of helium, which was found to be very similar to that of the sun. This implies that helium has not rained down or settled toward the center of the planet as much as on Saturn. As a result of this experiment, scientists now conclude that there has been very little change in helium abundance in Jupiter's atmosphere since the birth of the solar system.

To the layman, these and other early findings from the probe mission may seem arcane, but as NASA Ames Chief Scientist Richard Young writes in a recent issue of Planetary Report: "In many instances, new questions have been raised. This, of course, is how planetary exploration works. New information changes old ways of thinking and raises new questions to explore. In this way, our overall understanding of the solar system increases."

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