|
|
NOVA scienceNOW: Saving Hubble
|
|
|
|
Viewing Ideas
|
|
|
Before Watching
-
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 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.
-
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 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
-
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.
-
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.
-
A single spacesuit costs ___________.
- $1200
- $12,000
- $120,000
-
$12,000,000
-
Each spacesuit weighs about __________ pounds on Earth.
- 50
- 150
-
250
- 350
-
A spacesuit has _________ layers.
-
14
- 10
- 6
- 2
-
An spacesuit must protect an astronaut from ____________.
- extreme temperatures
- charged particles from the sun
- the low-pressure environment of space
-
all of the above
-
Which of the following materials is NOT found in a spacesuit?
- Kevlar®
-
Leather
- GORE-TEX®
- 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.
-
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.
- 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.
Web Sites
NOVA scienceNOW
www.pbs.org/nova/sciencenow/0303/01.html
Offers resources related to the Hubble servicing mission, including
additional activities, streamed video, and reports by experts.
Teachers' Domain—Hubble Telescope: Looking Deep
www.teachersdomain.org/resources/ess05/
sci/ess/eiu/lookdeep/index.html
Explains how the Hubble Space Telescope created the Hubble Deep
Field image of the early universe.
Teachers' Domain—Hubble's Expanding Universe
www.teachersdomain.org/resources/phy03/
sci/phys/fund/hubble2/index.html
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
www.pbs.org/wgbh/nova/rss/media/novasciencenow-20080603.mp3
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
www.teachersdomain.org/resources/phy03/
sci/phys/mfw/asrnt/index.html
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"
www.teachersdomain.org/resources/phy03/
sci/phys/mfw/freefall/index.html
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
dx12.jsc.nasa.gov/about/whatIsNB.shtml?link=2
Describes the pool facility used by NASA to simulate weightlessness
during astronaut training.
Hubble Site
hubblesite.org/
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
hubble.nasa.gov/
Official NASA Web site for the Hubble Space Telescope.
NASA—Suited for Spacewalking Educator Guide
nasa.gov/audience/foreducators/topnav/materials/listbytype/
Suited_for_Spacewalking_Educator_Guide.html
Provides background information and activities centered on the
history and technology of spacesuits.
Books
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.
|
|
