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NOVA scienceNOW: Saving Hubble

Viewing Ideas

Before Watching

  1. Explore the major discoveries of the Hubble Space Telescope. The Hubble Space Telescope (HST) was launched into low-Earth orbit (about 370 miles up) on April 24, 1990, aboard the Space Shuttle Discovery. In the next 18+ years, HST established itself as one of the most important telescopes ever, both for scientific discovery and public interest in astronomy. HST was designed to be maintained by shuttle astronauts and has been successfully serviced and repaired a total of four times to date. NASA is now preparing to send a fifth and final servicing mission to Hubble in the fall of 2008 before the space shuttle, and ultimately Hubble itself, is retired. Each upgrade and maintenance mission has improved the performance of the telescope—so much so that following the final scheduled repairs, Hubble is expected to be 90 times more powerful than it was at the time of its launch.

    To give students insight as to why the Hubble Space Telescope has been and continues to be such an essential contributor to scientific understanding of the universe, take them on a visual tour of Hubble's greatest accomplishments. Seeing some of Hubble's "greatest hits" before they view the segment will not only give students a clearer idea of what makes Hubble so valuable, it will bring the significance of the upcoming repair mission into focus. Project the images and descriptions of Hubble's Top Ten Discoveries. As a class, discuss the importance of each discovery. Have students take note of objects or phenomena they would like to learn more about.

  2. Simulate the difficulty of repairing instruments while wearing a space suit. During Hubble Servicing Mission 4 (SM4), scheduled for October 2008, astronauts will perform a series of spacewalks to install, repair, and replace several important instruments in an effort to improve the performance and prolong the lifetime of the Hubble Space Telescope. To complicate matters, repairs will be carried out while astronauts are "weightless" and wearing bulky spacesuits. The tasks the SM4 astronauts will attempt will require a great deal of dexterity, which can be extremely hard to achieve while wearing thick gloves.

    To help students understand the level of technical difficulty of these assignments in space, have them perform a series of tasks requiring increasing levels of dexterity while wearing multiple pairs of thick, stiff work or snow gloves. They can try to write their name, zip or button a jacket, or put together pieces of a jigsaw puzzle. Or have them try installing and/or removing small screws in an electronic device such as a radio or child's toy. Time how long it takes students to complete the task, first without gloves and then with them on. Were they successful? How much longer did it take them to complete the task while wearing the gloves? Did they drop anything? Remind students that dropping just one screw during an actual repair of the Hubble Space Telescope could have dire consequences. Worse even than just losing the item is the possibility that the "weightless" screw will drift into the telescope and cause severe damage.

  3. Demonstrate why astronauts experience the sensation of weightlessness in space. Many people mistakenly believe that the "weightlessness" experienced by shuttle astronauts is due to a lack of gravity in space. In reality, gravity is what holds the shuttle in orbit. Circling Earth at an altitude of about 320 km (200 miles), the shuttle and the astronauts inside it actually weigh around 90% of what they weigh on Earth. Even at the distance of the Hubble Space Telescope's orbit (600 km or 373 miles), gravity is still about 85% of what it is on Earth. So why then do astronauts float in space? The answer is that both the shuttle and the astronauts are in free fall, accelerating solely under the force of gravity. When two objects fall freely together (e.g., space shuttle and an astronaut), one can float, seemingly weightless, inside the other until they reach the ground. While in orbit, the space shuttle and HST are perpetually falling toward Earth—they have enough horizontal velocity that the curves of their paths are parallel to Earth's curvature , and thus they remain in orbit rather than crashing to the ground.

    Demonstrate the principle of free fall. You will need a cup made of paper or Styrofoam, and a bucket. Make a pencil-sized hole on either side of the cup near the bottom. Place your fingers over the holes and fill the cup with water, being careful not to let the water leak out. Hold the cup over the bucket, uncover the holes, and have students observe how the water pours out of the holes due to gravity. Have them predict what will happen to the streams of water if you drop the cup into the bucket. Next, refill the cup and hold it as high as you can above the bucket. Let the water begin to stream out. Then drop the cup into the bucket. Have students compare their observations to their predictions. While falling through the air, the water will stop coming out of the holes in the cup because both the cup and the water are in free fall, accelerating downward at exactly the same rate. Falling at the same rate balances the force that usually pushes the water through the holes—the hole has moved, getting out of the way of the water that is positioned to flow through the hole.

    To give students more time to observe what happens, you may want to stand in a stairwell, thereby increasing the height of the drop. If possible, you might also set up video recording equipment and watch the demonstration in slow motion.

    Explain to students that it is this same principle of free fall that is responsible for the sense of weightlessness experienced by shuttle astronauts. Emphasize that, though floating around may seem like a lot of fun, it can also be frustrating and increases the physical demands of an astronaut's work in space. Newton's Third Law of Motion (for every action there is an equal and opposite reaction) is every bit as valid in space as it is here on the ground. Whenever the astronaut pushes on an instrument or turns a screw, he/she experiences the same force pushing back on him/her. To simulate this, have students sit in a wheeled, swivel desk chair with their feet off the floor. Have them do different tasks, such as moving a stack of books from one place to another or opening a desk drawer or the classroom door. Use this to initiate a discussion about the importance of a tether and strong footholds and handholds for work in space—particularly for work conducted outside the confines of the shuttle.

  4. Demonstrate how astronauts are able to practice spacewalking on Earth. With so much at stake and only one chance to get things right, it is extremely important for astronauts to practice their work in a "weightless" environment before going into space. But, how are they able to escape gravity here on Earth? NASA uses two methods to simulate weightlessness. The first method is achieved with aircraft that follow the same steep parabolic flight paths that objects in free fall are exposed to. At the top of the arc, the contents of the aircraft (including the passengers) experience a brief period of weightlessness. However, at the bottom of the trajectory, passengers experience a force of about twice the normal force of gravity. The quick successive ups-and-downs often cause passengers to become sick, earning this type of plane the nickname "Vomit Comet." Not only does this method make people sick, it also allows passengers to experience weightlessness for just 20-30 seconds at a time—not nearly long enough to practice the intricate repairs shuttle astronauts will attempt when they visit the Hubble Space Telescope in October. The second way NASA simulates the sensation of weightlessness involves a giant swimming pool at Houston's Johnson Space Center known as the Neutral Buoyancy Lab (NBL). As students will see in the Hubble program segment, underwater training is the preferred method for spacewalk preparation.

    The NBL uses the principle of neutral buoyancy to generate the sensation of weightlessness. Neutral buoyancy occurs when the downward force of gravity on an object is exactly balanced by the upward buoyant force of the liquid in which the object is submerged. This means that the weight of the object is the same as the weight of the liquid it displaces. In a neutrally buoyant state, the object will neither sink nor float—it will hover. Scuba divers use this principle to maintain their depth under water by adjusting the amount of weight they carry and the amount of air in their life vests or buoyancy regulation jackets.

    While students cannot experience this directly for themselves in the classroom, you can demonstrate the principle of neutral buoyancy with a Cartesian Diver, which uses an eyedropper and a two-liter soda bottle. Fill the bottle with water. Partially fill the eyedropper with water and place it into the soda bottle so it hovers near the top of the bottle. Screw the cap onto the soda bottle to make it airtight. Squeeze the sides of the bottle. This will increase the pressure inside both the bottle and the dropper and will compress the air inside the eyedropper, causing it to sink. Carefully watch how the level of liquid inside the dropper changes. When you release the sides of the bottle, the eyedropper will move upward. Squeeze the bottle less firmly than before to get the eyedropper to hover near the middle of the bottle. When the eyedropper hovers in place, it is neutrally buoyant—gravity and the buoyant force are equal.

    For additional information about NASA's reduced-gravity training methods, have students explore the following NASA Web sites:

After Watching

  1. Take a stand on manned space missions. In the wake of the 2003 Space Shuttle Columbia disaster, former NASA administrator Sean O'Keefe announced that all future shuttle missions must be able to reach the International Space Station (ISS) in the event of an emergency that would prevent the shuttle from returning safely to Earth. Because the shuttle is not able to reach both the Hubble Space Telescope (HST) and the ISS during the same flight, the decision was made at that time to cancel Hubble's final servicing mission. However, it has since been reinstated under the condition that a second shuttle be prepared for launch should a rescue mission become necessary. NASA's concerns for astronaut safety are certainly well justified. Eighteen of the 430 people who have traveled in space have died during or as a result of a mission, which works out to a fatality rate of about 4%. For comparison, the National Safety Council has estimated that an American has about a 1.25% chance of dying in an automobile accident and about 0.02% chance of dying in a flying accident during his or her lifetime. When it comes to manned space flight, including the upcoming Hubble SM4, is the reward worth the risk? In the video segment, astronaut John Grunsfeld said "Going to upgrade and repair the Hubble Space Telescope, to serve science, to enable great science, and to enable great future discoveries—that's something that I believe is worth risking my life for." Find out if your students feel the same way.

    Have the students participate in a "Take a Stand" activity, in which they line up along an opinion continuum to compare and discuss their thoughts on various topics. Label one side of the room or board "Strongly Agree" and the opposite wall or end of the board "Strongly Disagree." Have students stand in the middle in the neutral or "undecided" zone to begin. Read a statement and ask students to line up between the two ends of the continuum in the location that they think best represents how strongly they agree or disagree with the statement. Students should discuss their opinions with one another and change their position on the continuum should they revise their opinions during the discussion. Use the suggested statements below, or develop your own:

    • Hubble's contributions to science are unique, and prolonging the life of this telescope is worth risking human life.

    • With the planned launch of the powerful James Webb Space Telescope in 2013, it would be a wiser decision to just wait and not service Hubble this one last time.

    • In the future, we should send robots rather than humans into space to perform space explorations.

    • If tickets were available and affordable, I would take a ride on the space shuttle.

  2. Test students' knowledge of astronaut attire. The extravehicular mobility units (also known as EMUs, or more commonly as spacesuits), worn by shuttle astronauts during a spacewalk, act as nearly complete spacecrafts built for one. They simultaneously provide astronauts with: protection from the harsh environment of space; oxygen to breathe; water to drink; and a communication line to the shuttle. There are many interesting yet little-known facts about these amazing garments. For example, in the video, astronaut Mike Massimino says that spacewalking astronauts wear their space suits for up to eight hours and that even though the suits are equipped with drink bags inside the helmets, they have no access to food. They also don't have access to a bathroom during a spacewalk, which is why an adult-sized diaper, called a Maximum Absorption Garment (MAG), is one of the 18 separate items that make up the modern EMU. Challenge students with the following multiple-choice questions about some of the most intriguing facts about spacesuits.

    1. A single spacesuit costs ___________.
      1. $1200
      2. $12,000
      3. $120,000
      4. $12,000,000

    2. Each spacesuit weighs about __________ pounds on Earth.
      1. 50
      2. 150
      3. 250
      4. 350

    3. A spacesuit has _________ layers.
      1. 14
      2. 10
      3. 6
      4. 2

    4. An spacesuit must protect an astronaut from ____________.
      1. extreme temperatures
      2. charged particles from the sun
      3. the low-pressure environment of space
      4. all of the above

    5. Which of the following materials is NOT found in a spacesuit?
      1. Kevlar®
      2. Leather
      3. GORE-TEX®
      4. Spandex®

    NOTE for teachers: Kevlar® is commonly used to make body armor and bulletproof vests, and GORE-TEX® is a waterproof/breathable fabric commonly found in outdoor clothing.

  3. Explore what NASA has planned beyond Hubble. Despite their successes and importance to space exploration, both the Hubble Space Telescope and the space shuttle are scheduled for retirement in the next few years. Have students explore what NASA has planned for the next phase of space exploration, specifically the James Webb Space Telescope (JWST) and the Orion spacecraft. Have students use the information provided in the Web sites listed below to compare HST and the space shuttle with their successors, and write a brief summary of how JWST and Orion are expected to advance space exploration.

  4. Investigate one of Hubble's major discoveries in more detail. Assign students one of the topics from the list that follows and have them research in more detail what Hubble learned about the object or phenomenon and the impact that it has had on scientific understanding. Each student or small group of students should prepare a poster, PowerPoint slide show, or some other type of presentation about their topic. The presentation should include at least one Hubble image related to the topic, a description of the object, details about the observations, information about where the object is located relative to Earth (if applicable), how scientific understanding was advanced by Hubble's observation(s) of the object or phenomenon, questions still remain about the object or phenomenon, and any other information the student(s) wish to include in their presentation.

    • Planetary nebula
    • Black hole
    • Hubble Deep Field/Hubble Ultra Deep Field
    • Supernova
    • Gamma ray burst
    • Quasar
    • Protoplanetary disk (proplyd)

    Refer students to the following Web sites as starting points for their research:

    Students can search the "Picture Album" by object name. Once an image is chosen, use the appropriate links provided to find additional information and images of the object.

    Students can search the archive by keyword. Using the keyword "Hubble" will bring up a list of images taken by HST, from which students can choose their object of interest.

Links and Books

Web Sites

NOVA scienceNOW
Offers resources related to the Hubble servicing mission, including additional activities, streamed video, and reports by experts.

Teachers' Domain—Hubble Telescope: Looking Deep

Explains how the Hubble Space Telescope created the Hubble Deep Field image of the early universe.

Teachers' Domain—Hubble's Expanding Universe

Describes astronomer Edwin Hubble's two most important discoveries—the existence of galaxies outside the Milky Way and the expansion of the universe—and explains the impact these discoveries had on scientists' understanding of the universe and its beginnings.

NOVA scienceNOW Pod Cast—Hands on Hubble
Interview with astronaut John Grunsfeld, explaining the difficulties involved with the upcoming Hubble Space Telescope servicing mission.

Teachers' Domain—Newton's Third Law of Motion: Astronauts in Outer Space

Explains how Newton's Third Law of Motion, combined with the sensation of weightlessness, increases the physical demands and dangers of working in space.

Teachers' Domain—Free-Falling and "Weightlessness"

Explains how the sensation of weightlessness can arise from free falling, and how the space shuttle and astronauts can be in free fall for long periods of time.

NASA—Neutral Buoyancy Lab
Describes the pool facility used by NASA to simulate weightlessness during astronaut training.

Hubble Site
Provides news, images, and educational information about the Hubble Space Telescope and its science. Also provides step-by-step instructions for creating a scale model of the Hubble Space Telescope with easy-to-find supplies.

NASA—The Hubble Space Telescope
Official NASA Web site for the Hubble Space Telescope.

NASA—Suited for Spacewalking Educator Guide

Provides background information and activities centered on the history and technology of spacesuits.


Hubble: The Mirror on the Universe, Revised Edition
by Robin Kerrod and Carole Stott.
Firefly Books, 2007.
Explains objects and phenomena observed by the Hubble Space Telescope and provides a history of telescope use in astronomy, focusing in particular on Hubble.

Hubble: 15 Years of Discovery
by Lars Lindberg Christensen and Robert A. Fosbury.
Springer, 2006.
Showcases spectacular images captured by Hubble during its first 15 years in orbit.

Hubble: Imaging Space and Time
by David Devorkin and Robert Smith.
National Geographic, 2008.
Recounts the struggles and successes of the Hubble Space Telescope from its earliest days through its final servicing mission scheduled for October, 2008 and sets the stage for Hubble's successor, the James Webb Space Telescope, due to launch in 2013.

The Universe in a Mirror: The Saga of the Hubble Space Telescope and the Visionaries Who Built It
by Robert Zimmerman.
Princeton University Press, 2008.
Tells the behind-the-scenes story of the Hubble Space Telescope and the persistence of the scientists devoted to its development and success.

Final Countdown: NASA and the End of the Space Shuttle Program
by Pat Duggins.
University Press of Florida, 2007.
Reviews the 25-year history of the space shuttle and looks forward to what NASA has planned after the retirement of the space shuttle.

Walking in Space: Development of Space Walking Techniques
by David Shayler (Editor).
Springer, 2004.
Reviews spacewalking techniques, basic equipment requirements, training methods, and steps to ensure crew safety during spacewalks.

Activity Author

Erin Bardar is a curriculum developer in Cambridge, MA. She has a bachelor's degree in Physics from Brown University and a doctorate in Astronomy from Boston University. In addition to writing physics, astronomy, and Earth science curriculum for a number of projects, Erin also created the Light and Spectroscopy Concept Inventory for evaluating college astronomy students' understanding of light and spectroscopy, and she has a U.S. patent for a binocular spectrometer.

Teacher's Guide
NOVA scienceNOW: Saving Hubble

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