Earlier this spring, we profiled Marc Church, a mechanical engineer at Lockheed Martin. As a follow-up to the profile, Marc invited questions from teachers, students, and families related to his work as a mechanical engineer—and his work on spacecraft.
We are posting his answers to your questions below. Thanks so much to Marc for his generosity in sharing his time, experience, and knowledge with all of us!
If you are interested in learning more about the career of a mechanical engineer, check the Science Buddies mechanical engineer career profile.
What is the coolest project you've ever worked on?
The coolest project that I've ever worked on was, unfortunately, the result of a catastrophe. On February 1, 2003, the 7-astronaut crew of STS-107 lost their lives as the space shuttle Columbia blew up upon re-entry into Earth's atmosphere. Why did it happen? A large chunk of foam insulation broke off of the external fuel tank during liftoff.
It was a tragedy, but every dark cloud has a silver lining. I was able to help redesign the area where the foam came off. Two-and-a-half years after the accident, we returned to flight with STS-114 on July 26, 2005. Seeing the space shuttle flying again with hardware that I helped redesign was one of the proudest moments of my life.
During those two-and-a-half years, I learned more than I had in my whole career up to that point. I learned what it really took to design space hardware with all the requirements and testing necessary to make sure that our astronauts are safe. I was able to participate in some very cool testing with cryogenic (-423°F) liquid helium that represented the liquid hydrogen fuel that the external tank carries to feed the SSMEs (Space Shuttle Main Engines). I was also able to experience testing in wind tunnels, which simulate the space shuttle during launch at twice the speed of sound (mach 2).
I also learned about the hard work, dedication, and sacrifices that are a necessary part of the process. My teammates and I worked long hours and weekends, and traveled for weeks at a time, spending a lot of time away from our family and friends. However, we did it! Today, the space station is complete because of our efforts.
What could top that, you ask? I'm currently building a spaceship, Orion, to put a man on both the Moon and on Mars. I can envision a future moment when I stand outside and look up at the Moon with my daughter, Catie, and realize that there is a man on the Moon because of my efforts.
If you were to pick a science fair project to do today, what would it be?
I recently judged a science fair here in Houston, Texas and was impressed by the number of projects that were related to energy efficiency. Besides my day job doing thermal analysis of spacecraft, I also have an interest in energy-efficient buildings and reducing the amount of energy and resources we use on a daily basis.
Last year, I took a test to become a LEED-accredited professional or LEED AP. LEED stands for Leadership in Energy and Environmental Design. You'll start to see more and more buildings, schools, houses, and hospitals trying to become LEED certified. Why, you ask? Well, a LEED-certified building can reduce energy use by 25–50%, water usage by 20% or more, and reduces and recycles the construction materials needed to build it. Therefore, the building owners save money and use less of our resources, like coal and oil, which are needed to produce the electricity. LEED buildings are also brighter and healthier for occupants than non-LEED buildings, because they have highly efficient glass windows (where most of the energy enters/escapes in a building) and paints and materials like carpet with low or no VOCs (volatile organic compounds).
Thus, I would probably do a science fair project related to testing windows that would automatically darken when the sunlight shines on them, or lighten when the sunlight doesn't shine on them. This would help save money by reducing the amount of heat allowed into a building. I would also consider a science project related to capturing rain water from the roof of a house in such a way that it could be used to flush toilets or water the yard. Water is expensive these days!
How much air do you need to carry to go to space?
There is no air in space because it is a vacuum. In order for astronauts to live in a spacecraft, they need an environment similar to Earth! They must have air to breathe, food to eat, water to drink, and a comfortable temperature.
Earth's atmosphere is a mixture of gases (78% nitrogen, 21% oxygen, 1% other gases) at a pressure of 14 pounds per square inch (psi). (If Earth were not pressurized, the vacuum in space would crush it like a soda can. The spacecraft must provide a similar atmosphere. To do this, liquid oxygen and liquid nitrogen are carried on board in two systems of pressurized tanks. The cabin pressurization system combines the gases in the correct mixture at normal atmospheric pressure.
Besides air, water is the most important element aboard a spacecraft. In the space shuttle, water is made from liquid oxygen and hydrogen in the fuel cells. The fuel cells can make 25 pounds of water per hour. The water from the fuel cells passes through a hydrogen separator to eliminate any trapped hydrogen gas. Excess hydrogen gas is dumped overboard. The water is then stored in four water storage tanks, located in the lower deck. Drinkable water is then filtered to remove microbes and can be warmed or chilled through various heat exchangers, depending upon the use (food preparation, consumption, or personal hygiene). Excess water produced by the fuel cells gets routed to a wastewater tank and subsequently, dumped overboard. So, how much? In terms of the space shuttle, it uses 7.7 pounds of nitrogen and 9 pounds of oxygen per day to provide breathable air and to pressurize the crew cabin. Assuming the longest space shuttle mission (17 days) means the following:7.7 pounds/day x 17 days = 131 pounds of nitrogen
9 pounds/day x 17 days = 153 pounds of oxygen
Total = 284 pounds of breathable air
How do you test the production models? And what kind of temperatures do they have to tolerate as part of Orion?
Testing and verifying that you meet the requirements given to you by your customer (NASA) are an essential part of spacecraft design and development.
For Orion, we have a variety of tests to meet the requirements. Let's start at the bottom (component level) and work our way up (spacecraft level).
Each component on the spacecraft is tested to ensure that it passes the environments it expects to see during a mission. The two predominant environments are vibrations (shaking of component due to vehicle acceleration) and thermal (temperature ranges). The component will undergo "shake and bake" testing under environments, based on the analysis and simulation predictions—which is what I do for a living. The environments are based on where the component is located on the spacecraft and to what it is attached, all based on the laws of physics. We add margin for error (making things worse) to account for any errors and unknowns in our analyses to ensure the components will work in space.
The spacecraft level is where all the components are assembled and you have your full spacecraft built. The spacecraft is put through a series of system-level "shake and bake" tests. For the "shake" test, a large shaker table is built to simulate predicted environments. For the "bake" test, we use a thermal vacuum chamber. We put the spacecraft in a vacuum to simulate space and chill the walls of the chamber to simulate the extreme cold environment of space (-454 degrees Fahrenheit). We then use heat lamps located around the spacecraft to produce heat to generate the hot space environments (due mainly to the Sun's energy and reflected energy off of the planet). The spacecraft is then powered on to make sure all the components and systems on the spacecraft work as designed. These tests are done to qualify the spacecraft.
After ground tests, we launch the real thing! For Orion, we will launch an unmanned spacecraft to approach the ISS (International Space Station) in 2013. We will then follow that up with a manned mission (2 astronauts) in late 2013 or early 2014!
Recently, Orion performed a major test for our Launch Abort System, which is used to move astronauts away from the rocket during the launch in the event of an emergency. It was a great success for our team, as they took all the components and integrated them into a system that performed perfectly. To quote our chief engineer, "it was like a stroll in the park!" A lot of hard work and dedication went into this test. You can view the test video here: www.nasa.gov/mission_pages/constellation/orion/index.html.
What are the best and worst parts of your job?
The best part of my job is working with cutting-edge technology and watching this technology get designed, built, and integrated to become a complex system that is used in space or here on Earth. I also get to work with some of the smartest people who are real-life rocket scientists. After the space shuttle Columbia exploded in 2003, I worked very hard with a team of people to fix the problems and get our space program back on its feet. I'll be honest, that was the hardest and most-complex work that I have ever had to do in my job. However, I had an incredible sense of pride and enthusiasm when the space shuttle launched again two and a half years later. It made all the hard work and "worst" parts of my job worth it!
As for the worst parts...in my current job, I spend a lot of time in front of a computer, which gets tiring at times. I also work in a cubicle, which is a partitioned office with no real walls, which can be distracting and loud at times. One day I hope to have my own office. I have a lot of meetings that I have to attend—it is hard to get work done when it seems you are always in meetings!
I'd like to learn about the toughest job you've worked on. What problems did you encounter, and how did you get through it? Do you have any tips on how to approach an engineering problem?
I've mentioned in some of the above postings about my work on the space shuttle external fuel tank after a piece of foam insulation broke off an area on the tank, punched a hole in the shuttle Columbia's wing, and eventually lead to its demise and the death of the seven astronaut crew on February 1, 2003.
The work that followed that incident was some of the toughest work that I have ever done. A few months before the accident, I changed departments from structural design to thermal analysis. I was assigned a thermal model, called the Bipod, with which I was supposed to get familiar. Well, I got very familiar with it, as this was the location where the foam insulation came off the tank and hit the shuttle. It was my job to redesign this area to remove all of the foam off of the top of the Bipod so that it would never be able to repeat what it did to Columbia on a future mission.
This model was an old model, dating back to the 1980s. It only existed as lines of code, like a computer program, no pretty pictures or high-tech software. I was on the hook to figure out how the model could be redesigned to make it safe for return to flight for the space shuttle. No sweat, right?
To make the design work we had to remove the foam insulation off of the top of the bipod fitting. The foam was there to begin with because the fuel in the external fuel tank is cryogenic; liquid hydrogen at -454 Fahrenheit....brrrrrr. If the foam wasn't there, ice (a lot denser than foam) would form on the bipod fitting and could break off during liftoff and hit the shuttle. We had to make a "hot plate" out of copper and put four heaters inside of it. We would then put the bipod on top of it such that the heat would transfer into it and keep it warm and ice-free. Sounds simple...right?
Well, it's always the unknowns that bite you. In this case, we learned a lot through testing a scale model of the bipod that we built from real parts. It turns out that the temperature sensors that we used to control the temperature of the hot plate were giving us fits. The wiring for the sensor was glued to the tank, which I mentioned was at cryogenic temperatures. Well, we found out that the temperature sensor wire was sucking all of the heat out of the sensors. So instead of telling us that the bipod was at a toasty 37 degrees Fahrenheit (above freezing) it was giving us a reading of -45 degrees Fahrenheit. This was late in the design process and it seemed like this was going to jeopardize our design. Ugh! What were we going to do?
The team worked together and came up with a solution that involved thermally anchoring the wire inside the copper plate. Without getting into too much detail, the wire coming out of the temperature sensor was kept warm for a long enough distance as to not suck out as much heat. We still had some error, but we understood that when it read say 10°F that it really meant 37°F. That's the way we fly it today!
My tips for approaching a problem....what are your knowns and unknowns? Draw a picture or a diagram and label it with the information you were given. Look for clues that can make the problem easier. In my world, these clues exist as assumptions and boundary conditions.
For example: A physics question might ask, "If you throw a ball in the air at a given speed of 20 miles per hour, what is the speed of the ball at its max height?" Well, I know that, according to physics and the laws of gravity, what goes up must come down. If I throw the ball up at a given speed, I know that gravity is going to slow it down until the ball reaches its maximum height, and then the ball will come down. At its maximum height, the speed of the ball is ZERO! From physics, I can use equations to figure out how high the ball went. Or if the ball was thrown at an angle, I can figure out how far the ball traveled horizontally.
My biggest tip to tackling an engineering problem is this: If you're not sure, ASK! There's no use pounding your head on your desk when a simple question to a teacher could turn on that lightbulb for you!
It sounds like the systems you are working on have to survive extremes of hot and cold. What kinds of things can you do as an engineer to protect the devices from damage?
I do have to protect the spacecraft, rocket, etc. from the extreme hot and cold. Let's start with the hot side.
During liftoff, as a rocket is racing to space, the air around the rocket creates friction, which, in turn, gives off heat. Therefore, we have to use materials called ablators that are placed on top of the metal (mostly aluminum) rocket to protect it.
An ablator is a material made up of cork, a binder or glue, and tiny silica (glass) spheres. The ablator erodes slowly, which allows it to dissipate the high heat due to air friction, while the remaining material keeps the rocket structure cool. You'll also find ablators on aeroshells, which are used when spacecraft enter the atmosphere of Earth or Mars.
A spacecraft in orbit around Earth might have a lot of electrical components that generate a lot of heat. Removing this heat so that the components do not exceed their operating temperature can be a challenge. One way to do this is to create a radiator. The radiator has a view to deep space, which is -454 degrees Fahrenheit. Through radiation heat transfer, the radiator can dump the heat generated by the electronics and keep them cool.
On the cold side, we use a couple of different methods. We can passively control the temperature by using control coatings and/or multilayer insulation blankets (MLI). Since the majority of heat lost in space is due to radiation (heat transfer through electromagnetic waves), the emissivity of a surface is important. The emissivity is the measure of a material's ability to reflect heat. In an MLI blanket, many layers of a thin film of Kapton are sewn together to make a blanket that minimizes heat loss. You'll easily spot MLI on spacecraft; it will be a shiny aluminum or in some cases, a gold-plated surface.
We can also actively control the temperature through the use of heaters. The heaters are attached on the component that needs to be warmed up. In order to use heaters, you need electrical power, which can be generated through the use of batteries stored on the spacecraft, or by harnessing the energy from the Sun, using solar arrays. Check out the massive solar arrays on the international space station!
Most spacecraft use both passive and active temperature control.
How do fins on a rocket affect its flight?
The fins on a rocket provide stability for the rocket during flight. During flight, the rocket could experience small gusts of wind or thrust instabilities that can cause it to wobble. The fins produce lift forces that "steer" the rocket back onto its flight path so that it remains stable. Larger, full-scale rockets do not rely on aerodynamics to steer them and do not have fins. They use gimbals, which allow the rocket engine nozzle to move and guide them during liftoff.
As an engineer, do you have to do a lot of math everyday?
I would say that I don't do a lot of physical math (adding, subtracting, multiplying, dividing, etc.) on a daily basis. I let computer programs like Microsoft Excel to do my dirty work! However, I deal with math all day when I'm building models for example. I use geometry to draw the models I need to represent the spacecraft. I also use a lot of things that I've learned in math classes to analyze data and read graphs. For example, I had to look up a value off a chart that had logarithmic scales. Had I not learned what the LOG scale was in math, I would have been unable to read the graph!
Math and science are essential to being an engineer. I know many people shy away from engineering because of math and science. Like anything else in life, though, a little hard work now will pay off tenfold later. Focus on the theories behind the math and science and it will make all the word problems and homework easier and less frustrating.
Do you think getting a master's degree after earning a bachelor's degree in mechanical engineering would be beneficial? Or would a master's lead to a job in a different (maybe more-specific, somehow) area of science?
I think that getting a master's degree after a bachelor's degree is very beneficial. I think it depends on what works for you. Some of my colleagues stayed in school after getting their bachelor's degrees before entering into a career. Others, like myself, waited until after starting a job. Most companies that hire for this line of work will pay for all or most of your master's degree, as long as you make a grade of B or above. Then, they'll give you a pay raise for getting your master's!
My best advice is to take getting a Masters degree seriously regardless of whether you do it right after your bachelor's degree or after you've started working for a company. I have yet to complete my Masters degree; it's something I hope to finish in the next few years. I was on the right path towards a degree but was derailed due to my workload at my job at the time. I didn't think I could devote the time to both school and my job. Looking back, it was probably just an excuse and I should have pressed on to finish my degree. Get it done early so that your career and outside distractions don't deter you!