## Classroom Activity

# Decoding Space Images With the DSN

### Overview

Students will learn how NASA communicates with faraway spacecraft using the Deep Space Network – including how data, such as images, are decoded. By decoding data themselves to reveal space images:

- Younger students will practice attention-to-detail and artistic expression.
- Middle-grades students will practice exponents.
- More technologically advanced students will practice spreadsheet skills.

### Materials

### Management

- Students can work individually or in small groups.
- Younger students will learn that in computer language, 1 means “on” and 0 means “off.” They will only need a pencil to complete worksheets I and II.
- Older students who understand exponents can complete worksheet III by hand using colored pencils or using spreadsheet software.

### Background

NASA’s Deep Space Network, or DSN, is a global network of antennae that we use to communicate with faraway spacecraft. With stations roughly every 120 degrees around the globe – near Goldstone, California; Canberra, Australia; and Madrid, Spain – the DSN provides a constant link to robotic explorers venturing beyond Earth’s Moon and to some Earth-orbiting missions. It's thanks to the DSN that we're able to receive never-before-seen images and scientific information captured by our missions. These data help us to better understand the universe, our solar system, and ultimately our place within it.

Data transmitted by a spacecraft via the DSN are encoded into binary code for transmission and then decoded on Earth. Binary is a base-2 number system that uses two states, 1 and 0, to represent a number. A bit is a single binary digit that is read by computers as on (1) or off (0). The number 10110100 is a sequence of 8 bits and is read as individual digits – one zero one one zero one zero zero – to distinguish from how we read decimal numbers. Standard notation for numerals in different base systems includes a subscript indicating the base, so sometimes a binary number will appear with a subscript of 2, such as 101101002. The subscript for decimal numbers is often omitted unless it is needed for context. Computers use billions of bit sequences to store complex information. These groups of 1s and 0s might not look like anything; however, in binary code, they translate to a message or image.

The reason that spacecraft and the DSN use binary code to communicate is that it's easier for computers to process than decimal notation or text, and it also takes up less memory. Binary transmissions can also better withstand errors from signal noise caused by interference. If a noisy transmission is received, as long as 1 and 0 can be differentiated, the message can be deciphered, cleaned, and restored to a pristine state of 1s and 0s.

In this lesson, students will work with bitmap images. Bitmap images are representations in which each item corresponds to one or more bits of information. Bitmap image files can store large images by breaking the image down into individual dots, called pixels, and assigning a binary number to describe how bright each pixel is. When a spacecraft camera captures an image, light passes through the camera’s filters to a detector chip, where the brightness of each pixel is recorded for each color filter (typically red, green, and blue, or RGB) to produce a color code for each pixel of the image. Separate bitmap images for each color are transmitted to Earth, converted back into RGB color codes, and then combined to create a single full-color image. In addition to colors, other filters can be used to pick out particular spectral lines that are of scientific interest.

In this lesson, students will encode and decode planetary images themselves, developing their academic skills while gaining an understanding of some of the complexities of obtaining information from faraway places. For simplicity, we skip the RGB codes used in real space image processing, which are in hexadecimal, or base 16, and instead provide students with suggested coloring schemes in binary code.

In this lesson, students will encode and decode planetary images themselves, developing their academic skills while gaining an understanding of some of the complexities of obtaining information from faraway places. For simplicity, we skip the RGB codes used in real space image processing, which are in hexadecimal, or base 16, and instead provide students with suggested coloring schemes in binary code.

### Procedures

This lesson can be leveled for various grades and skill levels. Separate steps for grade 4 and grades 5-9 are provided below.

#### Steps for Grade 4:

- Show students some images of Mars, Jupiter, and any other space objects of interest. Explain that these images are made up of thousands of square pixels, like pieces of a puzzle.
- Explain that faraway spacecraft send these images to Earth using “binary.” Binary means “two,” and the binary system uses 1s and 0s to tell computers whether a pixel is “on” (1) or “off” (0).
- Now, let’s transmit information! Hand out Binary Code Worksheet I. Explain to students that this worksheet shows sequences of binary digits, or bits, used by computers to create a white (1) and black (0) images.
- Have students decode the sequence, creating a bitmap image by coloring each square, or pixel, according to the binary code. Each line of code, or sequence, corresponds to a row on the bitmap. Do the first row together, and check student work by having them hold up their papers for visual examination. Explain to students that this is similar to how NASA's Deep Space Network decodes images sent by distant spacecraft.
- Continuing on Worksheet I, have students encode the provided bitmap by recording each sequence of bits, again using 1 for white and 0 for black.
- Now hand out Binary Code Worksheet II, and have students decode the larger bitmap.
- To check for understanding, have students describe what they are doing and how it applies to spacecraft communication.
- As an extension, have students create their own bitmaps and encode the data for their classmates to decode.

#### Steps for Grades 5-9:

- Based on your students’ knowledge of the Deep Space Network and binary code, follow the Steps for Grade 4 above that are most applicable to your students so they can gain an understanding of basic binary encoding and decoding. Have them complete the worksheets as necessary for practice.
- Explain to students that it's possible to decode the pixels for black and white images using 1s for "on" (white) and 0s for "off" (black), but to get color images, we need more information, so we use the binary number system.
- The number system students are used to is the decimal, or base 10, number system. Remind them that they are familiar with the ones place (10
^{0}), tens place (10^{1}), hundreds place (10^{2}), thousands place (10^{3}) and so on. In the binary, or base 2, number system, place value is similar, but instead of 10s we use 2s. Here are some examples to explain:

- In base 10, we can use the numerals 0-9 in any place value to represent a quantity. For example, the decimal number 5,672 = (5 x 1,000) + (6 x 100) + (7 x 10) + (2 x 1) = (5 x 10
^{3}) + (6 x 10^{2}) + (7 x 10^{1}) + (2 x 10^{0}) - In base 2, we can use the numerals 0-1 in any place value to represent a quantity. For example, the binary number 1101 = (1 x 2
^{3}) + (1 x 2^{2}) + (0 x 2^{1}) + (1 x 2^{0}) = 8 + 4 + 0 + 1 = 13 (in decimal, or base 10, notation)

- In base 10, we can use the numerals 0-9 in any place value to represent a quantity. For example, the decimal number 5,672 = (5 x 1,000) + (6 x 100) + (7 x 10) + (2 x 1) = (5 x 10
- Give students several examples of binary notation to decode into decimal notation (familiar quantities). Explain that standard notation for numerals in different base systems includes a subscript indicating the base. Here are some samples:

- 1000
_{2}= 8_{10} - 101
_{2}= 2^{2}+ 2^{0}= 5_{10} - 110011
_{2}= 2^{5}+ 2^{4}+ 2^{1}+ 2^{0}= 51_{10}

- 1000
- Provide students with Worksheet III, either electronically or in print. Explain that the numbers inside each pixel on the bitmap are in base 10, or decimal notation, but the color key is in base 2, or binary notation. Ask students which is easier to decode in this situation. Answer: It’s easier to decode the color key because there are fewer numerals to manage.
- Have students decode the color key, translating each color to decimal notation. Then, have them use the decoded color key to color in the first bitmap – either electronically or on the printout using colored pencils, markers, or crayons.
- Explain to students that the next two bitmaps are the same image as the first bitmap. Ask students what is different among the three bitmaps. Answer: The number of pixels is different. Ask what benefit more pixels provide. Answer: More pixels provide higher resolution and show more detail.
- Ask students what they expect the next two bitmaps will reveal. Accept all reasonable answers.
- Ask students to color in the next two bitmaps. If students are adept at spreadsheet software, have them use their skills to create a rule or script to color in the bitmaps. Alternatively, project each bitmap onto a blank classroom wall and have the class use different color sticky notes to create the image.
- Show students this image of Europa, one of Jupiter’s moons. Explain that it was compiled from many images captured by NASA’s Galileo spacecraft in the 1990s. Explain that the colored bitmaps the students created are lower-resolution versions of this same image. Ask students how higher resolution images might help scientists learn more about these worlds and explore them further.
- Have students research the Europa Clipper mission and discuss how early imagery of Europa set the stage for this new mission.

### Discussion

- Ask students why binary code is preferred to decimal or text transmissions.
- Ask students which role they found more difficult: encoding or decoding.
- Discuss the benefits of higher and lower resolution images. Better image quality leads to larger file sizes, which take longer to download. Similar file sizes with fewer bits are faster to download but do not provide as much detail.

### Assessment

- Students should be able to accurately encode and decode bitmaps. See answer keys below:

- Circulate and listen to evaluate students’ knowledge while working on Worksheet I and II. Scaffold as necessary for various learning levels.
- Attend to students’ discussions and observations to understand their knowledge.

### Extensions

- Have students create their own bitmaps for encoding by translating images to pixelated bitmaps and creating a binary code color chart. They can share these with peers to complete.
- If students are using spreadsheet software, have them experiment with various color keys to create their own “false color” version of the image.
- Have younger students try their hands at transmitting and decoding information with the Speaking in Phases lesson.
- Have older students learn about tracking spacecraft with the Tracking Spacecraft with Trilateration lesson.
- Have older students create their own three-color images of space objects using telescope images captured with red, blue, and green filters.

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