Liftoff to Learning: Space Basics
Table of Contents
|Video Title: Space Basics
Video Length: 20:55
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The Space Basics program tries to answer four basic questions
about spaceflight. How do spacecraft travel into space? How do spacecraft
remain in orbit? Why do astronauts float in space? How do spacecraft
return to Earth?
Subjects: The science and technology of orbits and microgravity.
Science as Inquiry
- Position and motion of objects
- Properties of objects and materials
Unifying Concepts and Processes
-Change, constancy, and measurement
- Evidence, models, and exploration
Science Process Skills:
Orbits and Microgravity
Although words like "satellite" and "orbit" are fairly
common terms in modern English, many people have little understanding
of the scientific concepts that make it possible for satellites to orbit
the Earth. When asked what keeps a satellite up, both children and adults
typically answer that satellites are beyond the pull of Earth's gravity.
If this were so, then why do satellites keep circling Earth? What keeps
them from shooting off into deep space?
| Satellites actually remain in orbit about Earth
because of gravity. More than 300 years ago the scientific foundations
for satellites were laid when Isaac Newton discovered the Universal
Law of Gravitation. He reasoned that the pull of the Earth that causes
an apple to fall to the ground also extends out into space to pull
on the Moon as well. Newton expanded on this discovery and hypothesized
how an artificial satellite could be made to orbit the Earth. He envisioned
a very tall mountain extending above Earth's atmosphere so that friction
with the air would not be a factor. He then imagined a cannon at the
top of that mountain that fired cannonballs parallel to the ground.
As each cannonball was fired, it was acted upon by two forces. One
force propelled the cannonball straight outward, and the second force,
gravity, pulled the cannonball down towards the Earth. The two forces
combined to bend the path of the cannonball into an arc ending at
the Earth's surface.
|| Isaac Newton's System of the World
Newton demonstrated how additional cannonballs would travel farther from
the mountain if the cannon were loaded with more gunpowder each time it
was fired. Eventually, a cannonball was fired so fast, in Newton's imagination,
that it fell entirely around Earth and came back to its starting point.
This became an orbit of Earth.
Without gravity to bend the cannonball's path, the cannonball would not
orbit Earth and would instead shoot straight out into space. The same condition
applies to Space Shuttles. The Space Shuttle is launched high above Earth
and aimed so that it travels parallel to the ground. If it climbs to a 200-mile-high
orbit, the Shuttle must travel at a speed of about 17,240 miles per hour
to circle the Earth. At this speed and altitude, the curvature of the Shuttle's
falling path will exactly match the curvature of the Earth.
Knowing that gravity is responsible for keeping satellites in orbit leads
us to the next question. Why do astronauts float in space? The answer
is simple. The Space Shuttle orbiter falls in a circular path about Earth.
Because the orbiter, astronauts, and all the contents of the orbiter (food,
tools, cameras, etc.) are falling together, they seem to float in relation
to each other. This is comparable to the imaginary situation that would
take place if the cables supporting a very high elevator would break,
causing the car and its passengers to fall to the ground. (In such an
example, we have to discount the effects of air friction on the falling
car.) Since the motion of the falling car and the passengers are relative
to each other, the people inside seem to float.
One of the common questions children and adult visitors to the NASA Johnson
Space Center in Houston, Texas ask is, "Where is the room where a
button is pushed and gravity goes away so that astronauts float?"
No such room exists because gravity can never be made to go away. The
misconception comes from the television pictures that NASA takes of astronauts
training in a special aircraft. The aircraft is flown to about 40,000
feet above sea level and then put into a steep dive. The pilot attempts
to exactly match the speed of a falling object. Inside the cargo section
of the airplane, astronauts and researchers float about and perform brief
experiments and training activities before the pilot pulls the airplane
out of the dive. Indeed, for approximately 30 seconds during each dive
the airplane acts like the Space Shuttle in orbit or like the imaginary
The floating effect of Space Shuttles and astronauts in orbit is called
by many names. It is referred to as "freefall," "weightlessness,"
"zero-G" (zero-gravity), or "microgravity." Space
researchers prefer to use the term "microgravity" because it
better represents the actual conditions of Earth orbit. Thus, even though
freefall simulates the absence of gravity, very small (micro) gravitational
forces are still detectable.
Rockets are able to travel into space because of the action-reaction principle
described by Isaac Newton in his third law of motion. In modern terms,
the law is stated:
For every action, there is an equal and opposite reaction.
In other words, for an object (person, automobile, rocket) to move in
one direction, the object must push in the opposite direction. In walking,
for example, when a person pushes (exerts a force) rearward on the ground
with foot and leg muscles, the person's body moves in the opposite direction.
To travel to space, the Space Shuttle exerts a downward force with the
exhaust of its rocket engines (action) and moves upward in the opposite
direction (reaction). The force of the downward push and the upward force
on the Shuttle are equal.
Balloon rocket demonstrates Action/Reaction
To return from space, the Space Shuttle orbiter also takes advantage
of the action-reaction principle. Remember, a spacecraft in orbit is traveling
at the right velocity so that the curvature of the path in which it is
falling matches the curvature of the Earth. If the spacecraft slows down
slightly, the path it follows changes from a circular shape to a long
arc ending at the Earth's surface. To slow the orbiter, astronauts fire
rocket engines in the direction the orbiter is moving to apply a braking
force. Then the long fall to Earth's surface begins.
Altimeter - Device for measuring altitudes.
Apollo - Name of the NASA project to land astronauts on the
Barometric pressure - The weight of the atmosphere pressing
at any point above Earth's surface.
External Tank - The large brown tank that holds the liquid
propellants for the Space Shuttle's main engines.
Freedom 7 - The name of the Mercury spacecraft that Alan Shepard
rode for his historic suborbital flight on May 5, 1961.
Gemini - Name of the NASA project that orbited teams of two
astronauts above Earth.
Gravity - The attraction of all objects to one another due
to their mass.
Jupiter C - The name of the rocket that launched the United
States' first satellite, Explorer 1, on January 31, 1958.
Mercury - Name of the first NASA project that orbited astronauts
Microgravity - An environment, produced by freefall, that alters
the local effects of gravity and makes objects seem weightless.
Orbit - The periodic path taken by a satellite (spacecraft,
moon, or planet) as it revolves around another body.
Orbiter - The winged spacecraft portion of the Space Shuttle
that orbits about Earth.
Propellant - The combination of fuel and oxidizer burned in
Relative humidity - A measure of the amount of moisture in
the air compared with what it could hold at that temperature. (A relative
humidity of 50% means that the air is holding 50% of the water it
could hold at its current temperature.)
Robert H. Goddard - American rocket pioneer who invented the
Satellite - A smaller body (spacecraft, moon, etc) revolving
about a larger body.
Solid Rocket Boosters - The white, solid-propellant rockets
attached to the side of the external tank of the Space Shuttle.
Space Shuttle - NASA's manned space vehicle consisting of an
orbiter, external tank, and two solid rocket boosters.
Stack - The term for a complete rocket (all pieces joined together)
on the launch pad.
Werner von Braun - German-American rocket pioneer and leader
in the development of the Saturn V rocket.
The following hands-on activities can be used to demonstrate some of the
concepts presented in this videotape.
Instructions To illustrate what an orbit looks like, attach the string
to the small ball and hang it from the ceiling. The ball should hang just
below the middle point of the volleyball (the equator on a world globe).
In this model, the small ball is a satellite and the larger ball is Earth.
Try to make the satellite orbit about Earth. Begin with the satellite resting
next to Earth. Which direction should the satellite be pushed to make it
orbit? What would happen to the orbiting satellite if the string were cut?
Satellite Orbit Model
Volleyball or basketball
Note: A world globe with a stand can be substituted for the ball
and flower pot.
Instructions To show what would happen to a satellite if gravity
did not hold it, make a slit in the side of the tennis ball. Tie a knot
in one end of the ribbon, and stuff the knot through the slit. Hold the
ribbon in one hand and twirl the ball in a horizontal circle. What will
happen if you release the ribbon? Will the ball fly straight away from you?
(The ribbon makes it easier to see the path the ball travels.) Compare this
activity to the demonstration of the apple and the string in the video tape.
Ball and Ribbon
Cloth ribbon (1 m)
Museum Gravity Well
Take your class to a hands-on science museum. Many of these museums
have gravity well exhibits that permit experiments with orbits.
Small versions of gravity wells are also available at some toy and
novelty stores. Use small marbles or coins to represent orbiting
objects and roll them around the well. Observe the relative speeds
of rolling objects that are far from the center with those close
Instructions: Investigate the shape of orbits by drawing ellipses.
Set up the materials as shown above, with the pencil inside the loop. Hold
the string taut while drawing a line completely around the push pins. What
will happen to the figure if the pins are brought closer together? What
will happen to the figure if the pins are moved farther apart? Look up Kepler's
Laws in any astronomy text book or encyclopedia. The laws describe the orbits
of planets as ellipses. The same laws apply to the orbits of spacecraft
Drawing Ellipses I
2 push pins
Square of cardboard
Sheet of paper
Drawing Ellipses II
Sheet of paper
Instructions: As an alternative to the first ellipse investigation,
make ellipses by casting a shadow from a ball on a flat surface. Alter the
shape of the shadow by moving the spot lamp. How are ellipses and circles
Falling Coffee Cup
What do you think will happen if you drop it? Drop the cup from a height
of several feet into the catch basin or bucket. Does the water pour from
the hole as the cup falls? Why or why not?
Styrofoam coffee cup
Catch basin or bucket
Demonstrate the principle of weightlessness by filling the coffee
cup with water. With a pencil, punch a hole near the bottom of the
cup. Be sure to hold the cup over the catch basin as you do this.
Observe how gravity causes the water to pour through the hole and
into the basin. Next, place a finger over the hole. Refill the cup
The following books will provide additional information.
Allen, J.P. with Martin, M., Entering Space, An Astronaut's Odyssey,
Stewart, Tabori & Chang, 1984.Joels, K. M. & Kennedy, G. P., The
Space Shuttle Operator's Manual, Ballantine Books, 1982.Ride, S.,
Okie, S., To Space & Back, Lothrop, Lee & Shepard Books,
STS-41 Crew Roster
Commander: Richard N. Richards
D. Cabana (Lt. Col., USMC).
Mission Specialist: Thomas D. Akers (Maj.,
Mission Specialist: Bruce E. Melnik (Cmdr., USCG).
Mission Specialist: William M. Shepherd
To obtain biographic information, click on highlighted names