NOVA scienceNOW: Saving Hubble
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.
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
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
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.
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
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:
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
contributions to science are unique, and prolonging the life of this telescope
is worth risking human life.
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.
the future, we should send robots rather than humans into space to perform
tickets were available and affordable, I would take a ride on the space
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
- A single spacesuit costs
- Each spacesuit weighs about
__________ pounds on Earth.
- A spacesuit has _________
- An spacesuit must protect an
astronaut from ____________.
- extreme temperatures
- charged particles from the sun
- the low-pressure environment
- all of the above
- Which of the following
materials is NOT found in a spacesuit?
teachers: Kevlar® is commonly used to make body armor and bulletproof
vests, and GORE-TEX® is a waterproof/breathable fabric commonly found in
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.
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.
Deep Field/Hubble Ultra Deep Field
Refer students to
the following Web sites as starting points for their research:
search the "Picture Album" by object name. Once an image is chosen,
use the appropriate links provided to find additional information and images of
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.
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
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
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
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.
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
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
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.
Showcases spectacular images captured by Hubble during its
first 15 years in orbit.
Hubble: Imaging Space and
by David Devorkin and Robert
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
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
NASA and the End of the Space Shuttle Program
by Pat Duggins.
University Press of Florida, 2007.
25-year history of the space shuttle and looks forward to what NASA has planned
after the retirement of the space shuttle.
Space: Development of Space Walking Techniques
by David Shayler
Reviews spacewalking techniques, basic equipment
requirements, training methods, and steps to ensure crew safety during
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.