Dear Caroline,

Thanks for your letter. You clearly already have the first attribute required to be a rocket scientist: a love of space. We did some research and were surprised to discover that of all the animals launched into space, only two have been cats. In 1963, the French launched Félicette on a successful fifteen minute suborbital flight. Later that year, they launched another cat (which they didn’t bother to name), but this time, the rocket malfunctioned. Unfortunately, the sacrifice of these two brave cats was for naught because since then, not another cat has gone into space. Based on this, your decision to become a rocket scientist makes a great deal of sense.

Now to your question about rocket science. We contacted Natasha McKatt, who lives at NASA’s Kennedy Space Center. She’s spent many an hour napping in meeting rooms, on computers, and under desks so she has learned a great deal about rocket science. In fact, she recently had an article on rocket science published in Cat Physics Quarterly. She has graciously allowed us to reprint it here.

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CAT PHYSICS QUARTERLY, VOL. 42

It’s not rocket science.

He’s no rocket scientist.

I’m sure most of us have heard these expressions at one time or another. But is rocket science truly as difficult as these and other similar phrases imply? The answer to that is a resounding yes. For a rocket launch to be successful, hundreds of components and systems must operate properly. Even a single failure can result in an exploding fireball or a satellite crashing back to Earth.

So what exactly is rocket science? To answer that, let’s see what goes into building a rocket.

STEP 1. DESIGNING A ROCKET.

Designing a rocket isn’t as simple as drawing a tall pointy thing with a motor on the back. The design has to account for the type of rocket motors being used, the size of the satellite is being launched, as well as the rocket’s trajectory (its path to space). The design must also be strong enough to handle the forces the rocket will see during flight. Thermal protection on the rocket’s exterior surface must also be included in the design to protect the rocket from the high temperatures which are generated while traveling through the atmosphere at high speeds. Design Engineers are primarily responsible for coming up with the design, but they work with engineers from many other disciplines as well.

STEP 2. ANALYZING THE DESIGN

The design must be analyzed to ensure it will meet the necessary launch requirements. Three sets of data are required to do this analysis

* Rocket motor thrust. Propulsion Engineers calculate the expected rocket thrust based on either previous motor firings or mathematical models of motor performance.

* Aerodynamic forces acting on the rocket. This information is generated by Aerodynamicists using a combination of computer simulations, wind tunnel test data, and measured flight data.

* The rocket trajectory. Guidance Engineers use the thrust and aerodynamic force data to determine the rocket trajectory that will achieve the desired orbit.

With this information, the loads and heating the rocket will see in flight can be determined.

A. THERMAL ANALYSIS

Thermal Engineers use this data to determine the heating the rocket will see in flight and determine if the thermal protection included in the design will keep the temperature of the rocket below acceptable levels. Specialized computer software is used to calculate how hot the rocket gets as it flies through the atmosphere.

B. MECHANICAL ANALYSIS

Mechanical Engineers develop computer models of the rocket design to perform structural and dynamics analyses. Using computer simulations, the forces the rocket will see in flight are applied to these models to determine if the rocket will survive.

If the temperatures or loads are found to be too high, the rocket design is modified to fix the issue. Thus, the design/analysis cycle is an iterative process which continues until the design is shown to survive expected flight loads and heating.

STEP 3. BUILDING THE ROCKET

Because they contain thousands of pounds of explosive material, rocket motors are built at specialized facilities. Other structures such as those which connect the motors (called interstages), the fairing (protects the payload during flight), and structures for mounting components and the payload to the rocket are either built by the rocket manufacturer or a subcontractor. Electrical components and wiring also need to be built. This doesn’t even include the work required to build the satellite the rocket will be launching.

4. TESTING

Even though extreme care is taken during the manufacturing process, the possibility of defects always exists. To ensure the rocket will not fail, structural, dynamic, thermal, electrical, vibration, and shock testing is performed on the rocket structures and components.

STRUCTURAL TESTING

In a structural test, the loads the rocket is expected to see in flight are applied to the motors, interstages, and fairing. Because of the high loads involved and the potential danger if a structural failure were to occur, no one is allowed in the load bay (a specially designed room where the test is run) while the test is in progress. Special gauges measure the displacement and strains in the structure during the test. Strain provides a measure of the loads in the structure. The applied loads are computer controlled to follow a defined profile which slowly increases the loads and holds them constant at different load levels.

Each time the load is held constant, the test measurements are compared against the predicted analytical results. If the test results are at or below the analysis values, the test is continued. However, if the test deflections or strains exceed the analysis results, the test is stopped to prevent a possible failure. If this happens, the structure is closely examined to determine if it was built correctly and additional analysis is performed to understand the reasons for the test anomaly. If no suitable answer can be found, it may be necessary to scrap the structure and start over. Because this can cause significant delays and cost a lot of money, every effort is made to correct whatever caused the testing issue.

DYNAMIC TESTING

Dynamic testing is primarily performed to verify that the models generated to support the analysis of the vehicle are accurate. The most common form of dynamic testing is what’s called modal testing. In this type of test, low level loads are applied to the structure. Unlike in a structural test, these loads are designed to oscillate at different frequencies in order to see which frequencies cause the structure to resonate.

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This is the same effect you see in a car which starts to shake at certain speeds. The motion of the tires on the road produce an oscillating force on the car and the frequency of this force is related to the car’s speed. The shaking of the car occurs when the frequency of the force produced by the tires matches what is called the resonance frequency of the car. So in a modal test, we’re trying to find the resonant frequency of the structure to see if is matches what the analysis predicted.

Because the loads used in this type of test are small, there is no risk of damaging the structure. If the test and analysis results don’t agree, the analysis models are reviewed and revised to provide an accurate representation of what was measured in the testing. If significant changes need to be made to the model, it may be necessary to rerun some of the analyses to ensure the structure will survive flight.

ELECTRICAL TESTING

Prior to testing, each electrical component which be used on the rocket must be verified to operate properly. Each component is checked in as flight-like a manner as possible. Thus, it is hooked up to the same type of wiring and power supply that will be used in flight. Electrical Engineers then command the component to go through each of its functions while they monitor its voltage and operation. If the component passes, it gets tested. If it fails, it must be repaired and checked again.

THERMAL TESTING

In a thermal test, the component is heated and cooled to the maximum and minimum expected temperatures it will see in flight based on the analysis done by the Thermal Engineers. This testing is done in what’s called a thermal chamber which can accurately control the temperature inside it. The component is heated and cooled multiple times to ensure it will survive the temperature extremes during flight. The temperatures are cycled in this manner because metal expands and contracts as it heats and cools. Just as a wire will eventually break if you keep bending it back and forth, the expansion and contraction of the solder joints in the component can cause them to break, rendering the unit inoperable. After the thermal testing is complete, the component is operated to verify it is still working properly.

VIBRATION TESTING

Vibration testing is designed to make sure a component will survive the high frequency force oscillations it will experience during flight. The frequency and magnitude of the force oscillations for each component are calculated by Environmental Engineers using a combination of measured flight data, analytical tools, and scaling methods.

During flight, the combustion of the rocket motors and aerodynamic loads (aeroacoustics) on the rocket generate high frequency force oscillations which have the potential to damage the rocket’s components. This high frequency oscillation, called random vibration, causes the circuit boards inside a component to move back and forth which can break solder or wire connections. Using a vibration table, the derived vibration levels are applied to the component to make sure it will survive during flight. After the vibration testing is completed, the components are once again checked by the Electrical Engineers to make sure they’re still operating properly.

SHOCK TESTING

Shock represents a high force on an object which happens very quickly. In physics, this is called an impulsive load. If you were to drop your cell phone on the floor, it would experience a high force for less than a tenth of a second, experiencing what’s known as a shock event. In flight, there are two primary causes of shock: motor ignition and stage separation. Environmental Engineers calculate the shock levels these events will produce on the rocket’s components.

For a rocket motor to begin firing, a small explosive charge located at the forward end of the motor is fired. This device, called an igniter, shoots hot gases into the motor cavity igniting the motor propellant. The activation of the igniter and initial combustion of the propellant causes a shock event. Stage separation occurs after each motor has finished firing and requires that the interstages be split apart. To do this, a length of explosive charge contained in a metal tube is mounted around the interstage’s circumference. This device, called a linear shaped charge, produces a hot plasma jet which cuts through the interstage skin causing the motor to fall away. As is the case with the motor igniter, the linear shaped charge produces a shock when it’s fired.

The shock loads have the potential to physically break items mounted to circuit boards. Due to the nature of shock, it is necessary to use a shock hammer to develop the shock levels for a component during testing. A shock hammer is essentially a large pendulum (6 to 8 feet tall) with a heavy metal hammer mounted to the end. At the base of the pendulum is a thick metal plate that the component mounts to. The hammer is lifted into the air and released. When it hits the plate, a shock is transmitted to the component. Once the shock testing is finished, the components, there’re operation is once again checked by the Electrical Engineers.

5. ROCKET CONTROL SYSTEM DEVELOPMENT

One other thing we need to consider: how do we control where the rocket’s going? After all, a rocket isn’t like a drone you fly with a remote control. It’s moving too fast and you don’t have continual radio contact. Therefore a rocket must control itself, which requires an onboard computer and programming.

A rocket controls its direction by pivoting its motor nozzle. This produces a side component to the motor thrust which steers the rocket. The nozzle is moved by powerful hydraulic jacks (called actuators) which are part of the Thrust Vector Control system. This system is controlled by the rocket’s flight computer based on measurements of the rocket’s speed, location, and orientation. These measurements are made by a device called the Inertial Measurement Unit, which feeds its data directly to the computer.

Now the software in the flight computer isn’t just something you can buy at an electronics store. It has to be developed by Software Engineers for each rocket. The software has to understand the data it is seeing and calculate how to move the nozzle to keep the rocket on its programmed trajectory. Guidance Engineers provide the calculations used to command the movement of the nozzle. This work begins during the rocket design process and continues right up until days before launch when the final version of the software is transmitted to the flight computer.

6. SYSTEMS ENGINEERING

Considering all the different types of engineers involved, miscommunication of the information being shared between them is always a concern. Fortunately, there’s a type of engineer whose job it is to coordinate interaction between the groups. Systems engineers keep track of all the rocket’s requirements and determine the information needed from each group of engineers. They make sure the data is communicated properly and meets the needs of those using it.

7. ROCKET ASSEMBLY

When ready for launch, the rocket is assembled at the launch site in special clean rooms. Due to their height, most rockets are assembled on their sides. Once all the components are installed, the motors connected, and the payload placed inside the fairing, the rocket is slowly driven to the launch stand on an erector. At the launch stand, the erector rotates the rocket until it is vertical and sitting on the launch stand where it is bolted in place.

The people responsible for assembling the rocket, called field crews, receive special training because working in close proximity to a rocket can be extremely dangerous. Even after the rocket is on the launch pad, they continually monitor the rockets systems and perform final checks on all the components. Often field crews are at the launch site for over a month prior to launch.

STEP 8. AND THEN FINALLY: LAUNCH!

Look at all the different skills required to bring a rocket from the drawing board to the launch stand. Rocket science is no one thing, but a symphony of specialties working together to create a thing of beauty: a successful flight to orbit. Yes it’s difficult to launch a rocket, but because of the shared commitment of those involved, rocket launches succeed over 90% of the time.

So next time you hear someone say, “it’s not rocket science,” consider the teamwork and attention to detail that goes into launching a rocket. I suspect many things could be improved if they were just a bit more like rocket science.