Make a Mockup

Rocket scientists, after they are finished dreaming, go through three stages called design, build, and test. The design may start innocuously with a sketch on a paper napkin during lunch. Before actually building a spacecraft, more accurate drawings, namely blueprints, must be made.

Of course, a great deal of analysis and simulation must be done first so that the hardware depicted in the blueprint accurately reflects the capabilities the spacecraft must have to achieve its mission. Spacecraft accoutrements typically include thrusters, pro-pellant tanks, sun and star sensors, gyros, accelerometers, antennas, computers, solar arrays or nuclear batteries, and a host of other navigational, life-support, and scientific equipment. Sometimes, engineers get so involved with these details that they forget to look at the big picture (the blueprint) to see how it's all put together.

I have noticed this tendency in my senior design students. Students are reluctant to draw a picture or create a CAD (computer-aided design) drawing of their spacecraft. They become mired in a sea of calculations on orbital mechanics, material strength, power requirements, telecommunications, and so on. And yet it is the picture that makes the design credible (assuming that all the relevant hardware is depicted and that the calculations are correct). A picture with dimensions and locations of all the major subsystems demonstrates the feasibility of the design. Nearly every piece of equipment requires power, occupies volume, and adds to the total mass (or weight). And mass on a spacecraft means money. The problem rocket scientists face is: How do I fit all the stuff I need into this spacecraft—and within the weight limit?

Let's say you are a backpacker about to hike down to the bottom of the Grand Canyon and camp for a few days. You ask yourself three questions. How much stuff do I need? Will it all fit in my backpack? Will it be too heavy? The answers turn out: lots, no, and yes! Now you can start thinking like a rocket scientist by unpacking and repacking. You examine each piece of gear and eliminate the dispensable. You consider how one piece of equipment can serve multiple purposes. Do you really need to carry a fork, a knife, and a spoon? Or will a spoon serve all three functions in a pinch? These kinds of questions can lead to new inventions or ways of doing things—like the spork, a combination spoon and fork. (It sounds dopey, but it works.)

When you go through this process of packing and repacking your backpack, you are performing a type of simulation that rocket scientists call a mock-up. A set of blueprints is usually not enough to answer all the questions that come up in spacecraft design. Rocket scientists often build a three-dimensional mock-up. It may be a small-scale model at first, followed by a full-scale model. For piloted missions, full-scale mock-ups are requisite. In the movie Apollo 13, the need for a mock-up is dramatically demonstrated as astronauts on the ground test out emergency procedures before implementing them on the real spacecraft. Three-dimensional mock-ups tell us if all the equipment fits, if the instruments and controls are well placed, if the astronauts are able to perform their mission.

Artists and architects use scale models for similar reasons. The nineteen-foot statue of Abraham Lincoln that sits in the Lincoln Memorial was designed by Daniel Chester French first as a small-scale model, then a larger model, and finally the real thing. The 151-foot Statue of Liberty was scaled up from the original four-foot model designed by the French artist Bartholdi. The index finger on the actual statue is eight feet high, and the total weight of the statue is 225 tons. It is inconceivable that a sculpture of this magnitude could have been built without the use of scale models.

Not all mock-ups are sophisticated or precise. As mentioned before, rocket scientists have used Tinker Toys to build simple

Chapter 30 Make a Mock-up mock-ups of spacecraft so they could easily visualize the vehicle's configuration and motion in three dimensions.

So, after drawing pictures, rocket scientists often turn to three-dimensional representations. These mock-ups are used to simulate and solve design problems. Whether they are constructed out of virtual images, plywood, plaster, or Tinker Toys, mock-ups are a crucial thinking tool in the rocket scientist's arsenal.

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