Alex A. McCool Jr. has worked on design of the propulsion systems for every flight of the U.S. Space Shuttle.
Eight and a half minutes.
To most of us, it's barely a blip, a period of time that goes by so fast we hardly notice it.
But for astronauts aboard the Space Shuttle and for the engineering team supporting them, it's the longest period of time imaginable.
Eight and a half minutes is the time it takes for the Shuttle to go from liftoff to orbit, to go "up hill," as NASA engineers say, and it's one of the most critical times in any Shuttle mission. It's where all the fire and smoke are, and much of the risk. When this propulsion phase is over and the astronauts enter orbit, the engineers of the Mission Management Team at Florida's Kennedy Space Center begin to breathe easy again. They have gotten the Shuttle off the ground, and now another team will take over control of operations. It's time for handshakes and high fives.
Return with us to November 30, 2000, as we peer through the glass at Kennedy's Launch Control Center. It's the nine -minute mark, and NASA has just successfully launched Endeavor on the 101 st Shuttle Mission. It will carry the 240-ft, 17-ton solar arrays to the International Space Station, quintupling its power. This is the heaviest and largest element ever delivered to the Space Station aboard a Shuttle.
You'll spot him in an instant. Walking briskly from station to station, a trim, wiry engineer with the broadest smile in the room slaps the backs and shakes the hands of everyone involved, congratulating them, joking with them, and spreading his own enthusiasm until it fills the control center.
Alex A. McCool, Jr., mechanical engineer, manager of the Space Shuttle Projects Office at the Marshall Space Flight Center (Huntsville, AL), noted propulsion-system expert, and universally acknowledged personification of the spirit of the Space Shuttle program, is beaming with pride and doing his thing. The true booster behind the Shuttle, he is pumping up his team while at the same time making mental notes of technical issues he'll ask them to tackle tomorrow.
At an age when many others would have long since retired and taken up golf, Mac McCool, 77, still exudes a passion for his work that people half his age would have a hard time matching.
"I still get chills talking about the launches," he says.
And, say those who know him best, he makes sure everyone else on the team is excited too.
For as much as he is a leading rocket engineer, McCool is a leader of people, unique in his concern for his team, say his colleagues.
"Alex rallies people and helps everyone to feel good about what they do here," says Art Stephenson, director of the Marshall Space Flight Center. "He is the father figure for the Shuttle program, and is one of the main reasons for the staff's high morale."
"He's my mentor, and in fact the mentor of many of the people here," adds Sid Saucier, associate director of Marshall.
He also is extremely knowledgeable, says George Hopson, Space Shuttle main engine manager. "Whenever there's a technical problem, we know we can turn to him because he has probably dealt with a similar problem in the past."
And that past is an illustrious one.
McCool has worked on the propulsion systems—the solid rocket boosters, external tank, and Shuttle main engines—for all 102 Shuttle missions. And, he was deeply involved in modifications of the Redstone rockets that propelled Alan Shepard and Gus Grissom on their historic Mercury flights. He sized the propellant tanks and did feed-system analysis and rocket engine testing for the Apollo program, ran NASA's Structures and Propulsion Lab, and headed safety and quality assurance efforts at the Marshall Space Flight Center for five years.
In the powerhead system, the high pressure turbopumps inject propellents into the main combustion chamber.
But the Shuttle has been his main professional passion, and, say his colleagues, he has watched over its development and that of the Shuttle propulsion team like a father nurturing a favorite child.
Both Byron Wood, vice president and general manager of Boeing/Rocketdyne, and Forest McCartney, vice president of launch operations for Lockheed Martin Astronautics, key NASA contractors, praise McCool's technical acumen. "He always poses the key question needed to put to bed the issue of whether we really are ready to launch—even if launch is only an hour away," Wood says.
Adds Ron Dittemore, NASA's top manager for the entire Shuttle program, "He is a unique leader who knows the real ingredients for making a complex engineering project like the Shuttle hum. When he talks, people listen because we all want to learn from the past."
Dittemore adds that McCool is a walking corporate memory. "Alex has been here since the Earth cooled," he says.
Launching the Shuttle requires the help of virtually every technology engineers can imagine, from motors to seals to pumps, sensors, exotic materials, and more. And, it requires the management of huge teams of engineers within NASA and its myriad subcontractors, from Boeing to Lockheed Martin and others. McCool manages the entire propulsion effort through a core staff in Huntsville, to whom he delegates most of the technical details. "He suggests ideas, but doesn't tell us what to do," says Saucier. "And when he critiques a decision, you don't even know you've been criticized, because of the way he handles it."
Despite the rigors of the technology, McCool thinks of himself as first and foremost a people person. "It's the team, not McCool," he says, adding that he is never happier than when he is helping mold the thinking and careers of the younger engineering set. "He is an exceptional team builder, and has established the Shuttle program as a wonderful place for an engineer to work," says Parker Counts, manager of the Solid Rocket Booster Project for the Shuttle and an engineer who has worked with McCool for 30 years.
Just ask astronaut Nancy Jan Davis, who has flown three Shuttle missions. McCool hired Davis 21 years ago to work in the Structures and Propulsion Lab, where she did stress analysis for the Hubble telescope. Later, after the Challenger explosion, she worked for him on solid rocket motor redesign. "He was a great mentor, and made it possible for me to get my PhD," she says. "He pushes everyone to get more education, and encouraged me to enter the astronaut training program." Today, she is deputy director of flight projects at Marshall, and counts McCool as a close friend.
Or, check with Alex Adams, who currently leads safety efforts for the Shuttle in Huntsville. McCool brought Adams in as a University of Alabama engineering coop student in 1988. "He put me right in the middle of many of the teams working on return to flight after Challenger," Adams says. "He hired me after graduation, encouraged me to go to graduate school, and sent me to NASA headquarters in Washington for a year as a liaison between the Shuttle project and the headquarters team." Among the pieces of advice McCool gave him, he says: Put family first, and always remember that safety is the first engineering concern.
Lightning rod. Of course, keeping everyone excited about the Shuttle hasn't always been easy, despite its lofty purpose.
Approved in 1972, the combination space craft and aircraft changed space flight in many ways. Prior to the Shuttle, launching cargo into space was a one-way proposition. NASA could put satellites into orbit, but it couldn't bring them back easily. The Shuttle gave NASA two-way reusable transportation capability. Throughout the 70s, NASA worked on Shuttle design, including the design of insulating tiles that could withstand the heat of reentry. McCool worked on the propulsion technology. In 1977, NASA produced the Shuttle Enterprise—a nonspaceworthy craft that pilots used to practice approach and landing. In 1981, Columbia became the first Shuttle to go into orbit.
But critics inside and outside NASA have leaped on opportunities to criticize the Shuttle. Occasionally, supporters had to keep NASA staff and the agency's subcontractors from shooting at each other. For example, in 1983, on the sixth Shuttle mission, an upper stage—which separates from the Shuttle to take satellites into geosynchronous orbit—failed. The satellite tumbled into a lower orbit. NASA assembled a team in Seattle at the Boeing plant to investigate the cause, and Bill Lucas, then director of the Marshall Space Flight Center, put McCool in charge.
"There was a lot of finger pointing among the varied interests represented on the team," recalls Counts, "but Alex was calm and cool and cut through all of it. He never got defensive or put anyone else on the defensive, and kept the team on track." Eventually, the investigative team agreed that a specific motor in the upper stage had been the culprit.
Following the Challenger disaster in 1986, there were more poisonous darts aimed at the program. Congress as well as the general public demanded answers as to the cause of the explosion that killed all seven astronauts. McCool got the nod to be the senior NASA engineer working with the Navy, which was charged with finding and salvaging the solid rocket motor. The short-form history relates that the Navy found the Challenger parts, and engineering analysis of them confirmed the accident cause: a leaking
O ring that allowed 5,000F combustion gases to leak onto the external tank, burning into the structure and destroying the vehicle.
McCool's colleagues recall some additional details about the investigation, however.
There was intense pressure from every corner to find the cause right away, they say, pressure that could have led to hasty and wrong conclusions. Many assumed the cause was an engine problem, and some were ready to rush to that judgment. Even McCool himself thought the engine pump might have been the problem, but he refused to cling to that preliminary conclusion. He wanted more evidence.
He was right to wait.
"Despite the pressure, Alex kept telling us that it was more important to get it right then to get it fast," says Shuttle Engine Manager Hopson.
NASA had been able to get most of the data on engine performance from tracking satellites, but the data on high-frequency pump vibration was on tapes in a black-box-type storage system that fell into the ocean.
"He insisted that the high-frequency data was critical, that we couldn't make final determinations without it, and once the tapes were recovered he made sure they were protected and analyzed," Hopson says. That data helped lead engineers away from the engine and pump and to the O ring on the solid rocket motor.
Saucier, associate director at Marshall, also remembers McCool's calm, deliberate manner. "He wasn't the leader of the investigative team, but he pulled everyone together and helped focus our efforts," Saucier says. "None of us knew what caused the explosion, but he cautioned everyone not to jump to conclusions and to make sure we were thorough."
More than that, says Thiokol Propulsion's President Bob Crippen, who piloted the first Shuttle as a NASA astronaut, "I don't know that we could have returned to flying the Shuttle after Challenger without Alex McCool."
Self-effacing, McCool downplays his role. He shifts the focus to his own fears during the investigation, laughing at himself as he recalls a harrowing late-night ride on a Zodiak pontoon craft. The Navy had called him at home to say it had found the solid rocket motor segments, and ferried him to the recovery ship 140 miles out to sea. "I'm wearing Nikes and overalls and the waves were so high I couldn't see above them," he recalls. "Then we get to the ship and I have to climb a Jacob's rope ladder to get on it. Very scary, and exhausting."
Emphasis on safety. NASA spent the next two years redesigning the joint. McCool led the Structures and Propulsion Lab in its design review, including subscale and full-scale testing. The team's goal was to implement triple redundancy to prevent the joint from failing. At one point after testing a full-scale motor, he actually put his hand on the rocket to see if it was hot. "It wasn't hot, so I knew our design would work," he says.
After the Challenger investigation, he agreed to take on the new role of safety and quality assurance manager for all programs at Marshall. He reorganized all safety efforts, making safety priority one. He also led efforts to revamp quality processes both within NASA and among the contractors. Additionally, his team put together a procedure for an appeals channel where anyone can raise safety issues without retribution.
McCool's work in and concern for safety are praised throughout NASA. Norman B. Starkey, deputy associate administrator for NASA's space operations, says his "conscientiousness and dedication to assuring safe and reliable human access to space" are among the contributions he is widely recognized for.
While he advises a methodical, unhurried approach to problem solving in general, McCool doesn't hesitate to make quick decisions when they involve safety. Early in 2000, as engineers and technicians were preparing for one Shuttle mission, a workman broke a drill bit in one of the main engine's combustion chambers. The bit got stuck in the chamber wall and technicians couldn't remove it. Marshall Center Director Stephenson recalls that the staff didn't think it was a safety risk, but McCool wasn't so sure. Rather than fly with the drill bit there, he ordered the ground crew to pull out the engine and replace it with another. "With our liquid oxygen system, we don't want to take any chances of sparking from metal-to-metal impact," he says. While the engine change-out didn't delay the launch, it wouldn't have mattered to him if it did. "He has always told us not to get hung up in schedules or budgets and forget safety," says Adams.
McCool's mantra: "You have to err on the conservative side, always."
Perhaps McCool's concern with safety and his emphasis on the importance of people come in part from his spirituality. His colleagues unanimously call him a very religious man, and he admits to praying before every launch. While some are uncomfortable talking about their religious devotion, he brings it up often, not in a proselytizing way but to let you know his priorities. A Sunday School teacher at his Baptist church near Huntsville, he lists his spiritual and family life as his top two interests, followed by his work. Even his career has pointed toward the heavens, almost from the beginning.
After graduating from high school in Florida in 1942, he enlisted in the Navy and became a first class petty officer and machinist mate. His brother Jim, who was also in the Navy, encouraged him to study engineering after his discharge in 1946, and that led him to the mechanical engineering program at Southwestern Louisiana Institute (now the University of Southwestern Louisiana). Following graduation, he got a masters degree in fluid mechanics at Louisiana State University.
Next stop was the Army Corps of Engineers, which assigned him to work on hydraulics projects in Mississippi. The job was civil engineering, but his heart was in mechanical so, following a friend's advice, he went to Huntsville's Redstone Arsenal in 1954, where mechanical engineers were working on guided missiles.
It was a heady time in the emerging field of rocket technology. The legendary rocket scientist Werner von Braun was in Huntsville, and already talking about sending rockets far into outer space. McCool met him and decided he was a "no-nonsense, hands-on, wild-idea man brilliant at pulling people together." A von Braun assistant, William Schulze, invited McCool to join the Guided Missile Development Division to work on propulsion systems for the Redstone guided missile. It didn't take much convincing.
"Mr. Schulze laid out on the table a complicated drawing of all the components and subassemblies of the Redstone Missile system and then pointed to the rocket," McCool recalls. "He said, 'we work on this.' That's all it took." From that day on, McCool's career has been propelling people into space.
McCool does little hands-on engineering today. Like many high-level engineering managers, he spends much of his time in meetings, conferencing with Shuttle teams at Kennedy and at the Johnson Space Center in Houston, and performing administrative work, which he hates. What he loves is his mentoring role. "I'm the coach, and my priority is to develop the team for tomorrow's work," he says.
Does he think about retiring? No way. And those who work with him shudder at the thought that someday he might decide to sit back and relax in the sun.
"Every year, Alex asks me if I want him to retire," says Marshall Space Center Director Stephenson. "Why would I ever want that?"
After the 100 th Shuttle flight in October 2000, McCool told his staff to prepare for 100 more missions. And in fact, NASA has plans to keep flying the Shuttle at least until 2010. That's a lot more eight-and-a-half minute launch periods, but, says McCool, "As long as the Lord gives me the strength, I'll keep working on all of them."
The power behind the
The main engines. There are three Space Shuttle Main Engines (SSMEs), and they produce 375,000 lbs of thrust each at sea level and deliver 35 million hp. During ascent, they consume over 500,000 gallons of liquid hydrogen fuel and liquid oxygen oxidizer at the rate of about 3,000 gallons per second.
The SSMEs run for a total of about eight and a half minutes, continuing to propel the orbiter for six and a half minutes after the solid rocket boosters have separated from the vehicle. A major flight milestone is MECO—main engine cutoff—as the orbiter, traveling at about 18,000 miles per hour, nears orbit.
The engine uses a two-stage combustion process. In the first stage hydrogen and oxygen are injected into the two preburners to be partially burned at an extremely fuel-rich mixture ratio of one-to-one. The resulting streams of hydrogen-rich gas drive two high-pressure turbo pumps. These turbo pumps inject the propellants into the main combustion chamber at high pressure (3,000 psi), along with fuel and enough oxygen to establish second stage combustion. Expansion of the hot gases through the chamber and nozzle produces thrust.
The majority of SSME components are built by Rocketdyne Division of Boeing at Canoga Park, CA. Recently redesigned turbopumps are built by Pratt & Whitney, a United Technologies Company, at West Palm Beach, FL.
The external tank. The huge external tank holds the liquid hydrogen and liquid oxygen and supplies them under pressure to the three Space Shuttle main engines. The tank gets its orange color from a coating of foam that insulates the super-cold propellants and protects the tank from the effects of aerodynamic heating during ascent.
Stretching 154 feet in length, the tank is over half a football field long, 34 feet longer than Orville Wright's historic first flight in 1903.
The tank assembly consists of a liquid oxygen tank, an unpressurized intertank, and an aft liquid hydrogen tank.
The liquid oxygen (LOX) tank, located at the forward end, has a nose cone that reduces drag and heating and serves as a lightning rod. The LOX tank contains internal ring-like baffle structures that strengthen the tank and minimize sloshing of the liquid during flight. The LOX feeds into a 17-inch diameter line at about 2,787 lbs per second when the Shuttle's main engines are operating at maximum ascent power.
The external tank is known as the structural "backbone" of the Shuttle vehicle. A "thrust beam" running across the 28-foot diameter intertank distributes over six-and-half million pounds of solid rocket booster loads to the liquid oxygen and liquid hydrogen tanks during ascent.
The liquid hydrogen tank has an anti-vortex baffle that controls the motion of the fuel as it exits the tank through a siphon outlet into another 17-inch diameter line. The feed line flow rate is 465 lbs per second when the Shuttle's engines are at maximum ascent power.
When the Shuttle reaches orbit and the main engines shut down, special pyrotechnics fire to separate the tank from the Shuttle. It breaks up as it enters the earth's atmosphere and its debris lands in the Pacific ocean. It's the only element of the propulsion system that isn't re-used.
The tanks are built by Lockheed Martin Space Systems Company at New Orleans, LA.
Solid rocket boosters. The two solid rocket boosters each consist of two major components: the redesigned solid rocket motor, built by Thiokol Propulsion, a division of Alcoa, in Utah, and the solid rocket booster components, provided by United Space Alliance at Kennedy Space Center. The solid rocket motors provide the thrust, while the solid rocket booster components provide electronic controls, thrust vector control, and the parachutes that lower the spent boosters into the Atlantic Ocean. When these two major parts are integrated together, the flight configuration is referred to as a solid rocket booster.
Each booster has a thrust of about 3,300,000 lbs at lift-off. They provide 85% of the vehicle's thrust during the first two minutes of flight. At an altitude of about 27 miles, with the vehicle moving at about 7,000 mph, the boosters separate from the Shuttle. Each booster is lowered to the water by three 135-foot diameter main parachutes, the largest parachutes ever used. Recovery vessels return the boosters to Kennedy Space Center for refurbishment and preparation for another launch, thus making the Shuttle a vehicle for promoting recycling as well as space exploration.
Here are some of the engineering steps McCool and his team have taken to improve Shuttle safety:
Solid Rocket Booster
Hydrazine to helium. Each solid rocket booster aft skirt contains a thrust vector control system (TVC) driven by hydrazine, a highly toxic and volatile propellant. To eliminate this hazard, engineers are converting the TVC power system from hydrazine to helium, which doesn't require a fuel pump or gas generator, and therefore doesn't contain any ignition sources.
Redesigned turbopumps. New high pressure turbopump designs have eliminated about 900 welds from the pump designs. There are now no welds on the high pressure fuel turbopump, and only two on the high pressure oxidizer pump. "Welds can go critical in milliseconds, and many of them are in places where you can't inspect," McCool says.
Redesigned main combustion chamber and nozzle. A new large-throat main combustion chamber increases the area where hot gases are first expanded, prior to entering the main combustion chamber. This increased combustion area reduces overall engine pressures and temperatures. The new chamber is built from large castings and forgings rather than smaller pieces of metal welded together. The design simplifies the system of coolant channels that circulate super-cold liquid hydrogen around the combustion chamber, and reduces the number of welds requiring inspection.
Ceramic bearings. New ceramic (silicon-nitride) bearings have replaced 440-steel bearings in the main engine high-pressure turbomachinery—they show no measurable wear and are completely non-corrosive.
Single-crystal turbine blades. Advances in metal casting processes now allow for the production of main-engine turbine blades made from a single crystal, rather than the millions of crystals that compose other metal parts. This process results in turbine blades of exceptional strength and corrosion resistance.
Thermal coatings. These spray-on coatings, made of a nickel-aluminum-oxide mixture, protect turbine blades from temperature spikes.
Investment castings. They allow engineers to reduce the number of welds in a component, making the part more reliable, and reducing inspection time.
Single-tube heat exchanger. Eliminates welds that are hard to inspect.
Two-duct powerhead. Increases turbine life and decreases maintenance.
Better sensors. Engineers improved all flight-pressure sensors and high-pressure fuel-turbine-discharge temperature sensors, partly through changing the manufacturing process to eliminate contamination problems that would corrode the pressure sensors and cause a short circuit. Engineers also thickened the body of the turbine discharge temperature sensors and replaced a resistance-temperature device with two thermocouples.
Friction-stir welding. This is for the longitudinal welds in the liquid hydrogen and liquid oxygen tanks of the External Tank. It's a solid-state welding process that uses a non-consumable cylindrical tool. The tool has an auger-type pin that is rotated, plunged, and traversed along the weld joint using conventional milling equipment. The technique heats, plasticizes, and extrudes material around the tool to the back of the pin, where it consolidates and cools under hydrostatic pressure. Result: higher strength and ductility than possible with conventional fusion welding.
Weight reductions. Partnering with the Russians on the International Space Station required NASA to be able to launch the shuttle at a 51°inclination to the equator (firing the Shuttle up the Atlantic Coast, in effect) rather than the usual 28°inclination (firing due east). This compromise allowed NASA to meet up with the Russian Mir space station, orbiting up to a more northern Earth latitude than standard Florida-launched vehicles. However, this adjustment required an increase in the Shuttle propulsion performance. Engineers achieved that propulsion increase through boosting the Shuttle power-to-weight ratio. A major contribution to shuttle weight savings made by Alex McCool and his propulsion team was to convert major external tank components from aluminum-2219 to lighter aluminum-lithium alloy. The tank is now 7,500 lbs lighter, 30% stronger, and 5% less dense.