How Do You Protect Spacecraft from Space Debris?

Abstract

You might not think a chip of paint could cause a lot of damage, but what if it is traveling 18,000 miles per hour? That is the reality astronauts face on the International Space Station (ISS). Learn how engineers protect the ISS from space debris in this fun science project as you build your own model spacecraft shield and conduct your own impact tests!

Summary

Areas of Science

Space Exploration

Difficulty

Method

Scientific Method

Time Required

Short (2-5 days)

Prerequisites

None

Material Availability

Readily available

Cost

Low ($20 - $50)

Safety

Adult supervision required for using a saw

Credits

Ben Finio, PhD, Science Buddies

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https://www.youtube.com/watch?v=shrrwhTZ-kA

Objective

Build a model Whipple shield and test how its ability to absorb impacts changes with debris speed. 

Introduction

Space debris, also called space junk or orbital debris, can range in size from tiny chips of paint to pieces of broken rockets to entire defunct satellites. After decades of human spaceflight, lots of space debris has accumulated in orbit around Earth. Space debris poses a big hazard to spacecraft and astronauts because much of it is traveling at thousands of miles per hour. Even tiny particles can cause a catastrophic collision that can damage or destroy a spacecraft. Scientists can usually track larger objects in Earth's orbit and, when necessary, maneuver other spacecraft to avoid collisions. However, much space debris is too small to track, and there is a lot of it. Scientists estimate that there are over one hundred million pieces of space debris less than one centimeter wide! Micrometeoroids, small chunks of rock with a mass of less than one gram, pose a similar threat. 

So, how do you protect a spacecraft from collisions with debris that is too small to see or track? Engineers design shielding to protect spacecraft from impacts. While they cannot protect spacecraft from collisions with large debris, the shields can help absorb and break up the impact from smaller debris. The ISS has over 100 different shields! There is a problem designing shields for spacecraft, however. It takes a lot of energy to launch things into space. Therefore, launching heavy materials into space requires a lot of fuel and is very expensive. That means that you cannot just cover an entire spacecraft in thick, heavy metal plating or armor. Engineers have to design shields that are effective at stopping debris but are also lightweight.

One such type of shield is called a Whipple shield, named after astronomer Fred Whipple. A Whipple shield consists of one or more "bumper" layers spaced apart from the spacecraft's outer walls (Figure 1). The goal of a Whipple shield is not to completely stop debris. Instead, when a piece of space debris hits a layer of the Whipple shield at an extremely high speed, it shatters and breaks into smaller pieces that spread out (Figure 2). This spreads the impact over a larger area and makes it less likely that the debris will puncture a hole in the spacecraft's outer wall. Since space debris is so small and space is so big, the odds that another piece of debris will hit the exact same spot on the bumper layer are very low. However, astronauts may eventually replace the layers of shielding.

Image Credit: NASA / Public DomainN

Figure 1. The Whipple shield used on NASA's Stardust probe.

Image Credit: NASA / Public domain

Figure 2. Picture of a Whipple shield showing the initial small hole in the bumper layer (left) and the resulting spread-out debris pattern (right).

In this science project, you will build and test your own model Whipple shield. While you cannot make debris move thousands of miles per hour, you can still do an experiment to find out how variables like the size or speed of the debris affect the shield's performance. The project's procedure will show you how to build a Whipple shield with multiple layers and drop an object onto it from different heights to see how many layers the debris will penetrate. However, there are many other variables you can test. See the project's Variations section for more details. Do you think your shield can handle the impacts? Try it and find out!

Terms and Concepts

• Space debris
• Space junk
• Orbital debris
• Orbit
• Micrometeoroid
• Shielding
• Whipple shield

Questions

• What is space debris? Why is it dangerous?
• What are some approaches to dealing with space debris and keeping spacecraft safe?
• Do you think an object will penetrate more layers of a Whipple shield if it is moving faster?

Materials and Equipment

• Sheet of 3/4 inch thick plywood. Make sure the wood is flat and smooth, not warped or rough. You do not need a full 4×8 foot sheet of plywood. Many hardware stores sell smaller 2×2 foot sheets that will be sufficient. You can also ask if they have any pieces of scrap wood that you can have for free.
• Tape measure
• Sandpaper
• Aluminum foil
• Heavy weights like dumbbells or large rocks
• Small object to use as debris, such as a marble, ball bearing, or small rock
• Tape measure
• Large piece of scrap wood or another surface you can do the experiment on without worrying about damage to a floor or countertop

This project follows the Scientific Method. Review the steps before you begin.

1. Cut your plywood into at least 10 equally-sized squares.
   1. If you purchased a 2×2 foot sheet of plywood, you can cut it into 16 6×6 inch squares. If you have more plywood, larger squares up to 12 inches (the width of a roll of aluminum foil) will work well for the project. 
   2. Note that if you do not have access to a circular saw or table saw, many hardware stores will cut plywood for you.
   3. Sand any splinters or rough edges.
   4. Make sure the plywood squares stack neatly on top of each other and sit flat without any gaps.
   5. 10 plywood squares will allow you to make a Whipple shield with four layers, but you can add more.
2. Arrange the layers of your Whipple shield.
   1. Place two plywood squares side by side, with their edges parallel, leaving a gap equal to the side length of the squares (for example, if you cut squares with 6-inch sides, they should be 6 inches apart).
   2. Cut a rectangular piece of aluminum foil the same width as the gap but several inches longer than the gap.
   3. Place the piece of aluminum foil across the gap (Figure 4). Make sure it is pulled tight and not sagging.
   4. Place two more plywood squares on top of the aluminum foil to hold it in place. Make sure their edges line up with the squares below them.
   5. Cut another piece of aluminum foil and repeat the process until your Whipple shield has at least four layers of aluminum foil sandwiched between layers of plywood (Figure 5).

Image Credit: Ben Finio / Science Buddies

Figure 4. Initial setup for making the model Whipple shield.

Image Credit: Ben Finio / Science Buddies

Figure 5. A Whipple shield model with four layers of aluminum foil sandwiched in between plywood layers.

3. Carefully place a heavy weight, like a rock or dumbbell, on top of each stack of plywood (Figure 6).

Image Credit: Ben Finio / Science Buddies

Figure 6. Dumbbells placed on top of the Whipple shield to firmly clamp the layers in place.

4. Make a data table like Table 1.

Swipe left to see more

Drop height (cm)	Trial 1	Trial 2	Trial 3	Average
10
20
30
...

Table 1. Example data table to record the number of Whipple shield layers penetrated for each trial.

5. Set up a meter stick or tape measure to measure your drop height. It will be easiest to measure from the ground, so you can measure the height of the topmost layer of your Whipple shield and subtract it from the start height of your debris to calculate the drop height (Figure 7).

Image Credit: Ben Finio / Science Buddies

Figure 7. Meter stick set up to measure drop height. The top layer of the Whipple shield is at a height of 7 cm, and the marble is held at a height of 17 cm, so the drop height is 17 - 7 = 10 cm.

6. Start from a low height, for example, 10 cm, and drop your debris into the center of your Whipple shield.
7. How many layers of the Whipple shield did the debris break through (Figure 8)? Record your observations in your data table.

Image Credit: Ben Finio / Science Buddies

Figure 8. Close-up view of a marble that penetrated the first two layers of the Whipple shield and came to rest on the third layer.

8. Replace any damaged sheets of your Whipple shield and conduct two more trials from the same drop height. Even if your debris did not puncture any layers, you should replace the top layer for each new trial.
9. Increase your drop height by 10 cm and conduct three more trials. Remember to replace the top layer of aluminum foil, and any damaged layers, for each new trial.
10. Keep increasing your drop height until your debris breaks through all the layers of your Whipple shield. Add rows to your data table as needed.
11. Analyze your data.
    1. For each drop height, calculate the average number of layers that the debris broke through.
    2. Make a graph with drop height on the horizontal axis and the number of layers broken through on the vertical axis.
    3. What is the relationship between drop height and the number of punctured layers? 

Ask an Expert

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Global Goals

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.

This project explores topics key to Industry, Innovation and Infrastructure: Build resilient infrastructure, promote sustainable industrialization and foster innovation.

Variations

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