The engineering design process is a set of steps that engineers go through when they want to design a solution to a problem. There are three main steps that you can remember to help you understand the engineering design process, and they are: design, build and test. We are going to talk a little bit about each one of these steps, and then you are going to get to try them out yourselves.

Design: Before engineers build anything, they first have to figure out exactly what they are going to build. They determine out how big it should be, how much it can weigh, what shape it should be, and how much money can be spent building it. Oftentimes, they talk to the people who are going to use their design, and they decide what special features they want it to have.

Build: Once the engineers have finished their design and are happy with it, they can begin to build a model or a prototype of their design. Models are usually smaller than the actual design, and there are many different types of models - some look just like the design, but in miniature, and others only exist on the computer. A prototype is another version of the design. A prototype generally works just as the final design will, and it is an opportunity to work out and fix some of the trouble spots that might ─ and usually do ─ arise before the final product is built.

Test: Once the engineers have the model or prototype ready, they run many different tests on it: strength, waterproof or not, weight, breakability, etc. They run many tests (sometimes over and over again) to ensure that the product can do what they designed it to do. If their device fails a test, or if the engineers discover some sort of problem with it, then they go through the cycle again - they re-design, re-build, and re-test until it is exactly how they want it to be.

Now that you understand the design process, we are going to design and build our own devices to help the astronauts eat in space. Unfortunately, we will not get to travel into outer space to test our designs, but we can still do a great job on the design and build parts of the process!

Figure 6. Rehydratable shrimp cocktail. click for copyright

The seven forms of food are: rehydratable, thermostabilized, intermediate moisture, natural form, irradiated, condiments and shelf-stable tortillas.

Rehydratable food is food or beverages that have had the water removed. To prepare, astronauts just add the water back in and heat the food up in their on-board oven. Breakfast cereals can be pre-packaged with dry milk and sugar, and can be eaten once water is added. These foods can include soups, casseroles and appetizers (see Figure 6).

Thermostabilized food has been heat processed to kill organisms. These packages are heated, opened with scissors and eaten. This type of food is generally packaged in cans, plastic cups or flexible pouches. Food choices include beef tips with mushrooms, tomatoes and eggplant, and ham.

Intermediate moisture foods have just the right amount of water in them: not too wet (to prevent microbes from growing in the package) and not too dry (to help cut down on the amount of preparation for the astronauts). Essentially, these foods are ready to eat right out of the package, and they include dried peaches, pears and apricots, and dried beef (see Figure 7).

Figure 7. A vacuum-sealed back of apricots, an intermediate moisture food for astronauts. click for copyright

Natural form foods are ready to eat. They come in clear, flexible pouches that are cut open with scissors, and they include granola bars, nuts and cookies (see Figure 8).

Irradiated foods are meat products that also come in flexible, foil-laminated pouches, and have been sterilized by radiation. There are twelve kinds of irradiated meat products that are used, including: beefsteak, sliced turkey, breakfast sausage and fajitas. The FDA only permits a few foods for the general public to be irradiated (at very low levels), so NASA has special permission to irradiate meat at higher levels so that the meats do not need to be refrigerated. (Note: meats that the general public eats that have been irradiated at the standard, low levels still need to be refrigerated.) As we have learned, there are no refrigerators on the space shuttle, so irradiation at higher levels is very important.

Condiments include ketchup, mustard, mayonnaise, hot sauce, salt and pepper.

Figure 8. Vacuum-sealed bags of M&Ms and dried fruit, natural form foods. click for copyright

Since bread is bad news on the space shuttle ─ because the crumbs can get into the machines and affect their functioning ─ shelf stable tortillas are used instead. NASA developed special packaging for these tortillas, so they will not mold. Pretty nifty stuff!

• Gather all necessary materials.
• Print out the Design Worksheet (one per team).

1. Go over the seven forms of food with the students (from the Background section). Explain that these forms of foods help with the problem of eating in microgravity and demonstrate some of the solutions NASA engineers have developed for food during space flight. Tell to students that today they will become engineers from NASA and design a form of food or device to help the astronauts eat in space.
2. Write the three main parts of the engineering design process on the board: design, build and test. (Note: See the Introduction section for more on the engineering design process.)
3. Break students into teams of 2-3 and pass out worksheets (one worksheet per team).
4. Give students 8-10 minutes to work on their design and complete the worksheet. Encourage students to focus on a particular food or a specific challenge of eating in space. (Note: This is an open-ended design, so encourage creativity.) Students may not begin building until their worksheet has been checked off.
5. Once their team's worksheet is checked off, encourage students to begin building a model of their design.
6. To encourage use of mathematics, establish constraints on some of the supplies and have students measure out a certain amount. For example: "you may only use 0.4 meters of masking tape, and 2.3 meters of string." Students should work together to measure out the allowed amounts.
7. Allow time before the end of class for each team to present their idea and design to their peers.
8. Instruct groups to clean up.

Discussion Question: Solicit, integrate and summarize student responses to the following questions:

• Have you ever seen a picture or a movie of astronauts eating in outer space? It looks pretty funny, right? Why do you think it is so hard for astronauts to eat in outer space? (Write student responses on the board; possible answers include: they are homesick, the shuttle is spinning, they do not have a refrigerator, they do not have an oven, there is hardly any gravity, their food is floating around…)

With the students, come up with a list of foods that would be easy and foods that would be hard for astronauts to eat in space. (Make two lists on the board. Hard foods could be: spaghetti, cereal with milk, salad, etc. Easy foods could be: tortillas, lollipops, M&Ms.)

Student Interviews: As the students are working in groups on their designs, visit each group and ask them what they are learning about engineers as they build. (Possible answers: engineers are creative, engineers help people, engineers work in teams, engineers help astronauts, engineers have a design process, etc.).

NASA Engineering Team Presentations: Allow students to choose one team member to present their team's idea to the rest of the class or have both/all team members present together. The students should explain which problem their team is trying to solve, why their team chose a particular design, and any challenges their team faced in the engineering design process.