The Space Shuttle is a Lifting Body
On August 12, 1977 a specially modified Boeing 747 jetliner was giving
another aircraft a piggyback ride. Approximately 24,000 feet above
the Mojave Desert a high-tech glider was released from its flying
perch. It glided effortlessly without engine power to a smooth landing
on the desert floor. A new era in space transportation had begun.
That high-tech glider was the space shuttle. The space shuttle is
designed to simply ferry or "shuttle" people, satellites and other
cargo between earth and space. It is a reusable spacecraft unlike
any other that had come before it. It is a more efficient and economical
vehicle as compared to its predecessors: capsules and rockets. The
space shuttle, with a shape like a bulky glider, is actually a lifting
body. A lifting body is a specially constructed spacecraft that
cannot launch under its own power, but needs additional rocket engines
for thrust. The space shuttle is a unique lifting body in that it
is a high-tech glider.
Basic Structure
The space shuttle is made up of four parts: an orbiter (the shuttle
itself), two solid rocket boosters (both reusable) and one external
fuel tank (which is not reusable). This space craft is launched
in an upright position attached to the 2 solid rocket boosters and
the external fuel tank. At launch, the orbiter's 3 main engines
are fired (fueled by the external fuel tank) as well as the solid
rocket boosters. Together they provide the shuttle with the millions
of pounds of thrust to overcome the earth's gravitational pull.
The Orbiter as a High-Tech Glider
The orbiter is shaped much like an airplane. It has many of the
same parts as an airplane except for its engine configurations.
The orbiter has wings that create lift. It uses a double-delta wing
configuration to achieve the most efficient flight during hypersonic
speed as well as providing a good lift-to-drag ratio during landing.
For control, each wing has an "elevon". An elevon is a combination
of an elevator and an aileron. On an airplane, the
elevator controls the motion of pitch (nose up, nose down). On most
airplanes, the elevator is located on the horizontal stabilizer
as part of the tail section. The ailerons are found on most airplanes
at the trailing edge of each wing. Ailerons control an airplane's
roll motion. Because of the orbiter's delta wing configuration,
the elevators and ailerons are combined as elevons and placed at
the trailing edge of each wing. The orbiter's vertical stabilizer
(fin) has the rudder which controls its yaw (nose left, nose right).
The split-rudder on the orbiter works as a rudder and also a speed
brake (found on most airplanes as a spoiler located on the wing).
It does this by splitting in half vertically and opening like a
book. This deflects the airflow, increases drag and decreases the
orbiter's speed as it rolls along the runway upon landing.
The airplane-like control surfaces on the orbiter are useless
in the vacuum of space. However, once the orbiter re-enters the
earth's atmosphere, these control surfaces interact with the air
molecules and their airflow to control the orbiter's flight path.
The engines are the major difference between this high-tech glider
and airplanes. The orbiter has the OMS (orbital maneuvering system)
engines as well as the RCS (reaction control system) engines. The
shuttle maneuvers into orbit using its orbital maneuvering system
(OMS). The OMS has 2 rocket engines located on the outside of the
orbiter, one on each side of the rear fuselage. These rockets give
the orbiter the thrust it needs to get into orbit, change its orbit,
and to rendezvous with a space station or another space vehicle.
The OMS is also used to exit orbit for re-entry into the earth's
atmosphere.
The second set of small engines includes one set of engines near
the orbiter's nose and two other sets in the rear on the pods. These
reaction control system (RCS) engines allow the commander to perform
the motions of roll, pitch and yaw while the orbiter is maneuvering
out of orbit and into re-entry of the earth's atmosphere. The RCS
engines are also used while the orbiter is maneuvering in the upper
atmosphere.
Re-entry and Landing
The commander begins the de-orbit burn by firing the orbiter's engines
to slow its speed and take it out of orbit. Using the RCS engines,
the orbiter is turned around so that it is moving backwards at a
slower speed. To maneuver the orbiter while it is in this position,
the commander uses the RCS engines to control roll, pitch and yaw
motions. The OMS engines (space engines) are then fired, taking
the orbiter out of orbit and thrusting it into the earth's upper
atmosphere. The RCS engines are used one last time to turn the orbiter
around so that it is moving nose forward and pitched up slightly.
In the upper reaches of the atmosphere the vehicle's motions of
yaw, pitch and roll are controlled by the RCS engines. As the atmosphere
thickens, the airplane control surfaces become usable. The orbiter
re-enters the atmosphere at a high angle of attack (about 30 degrees).
This high angle of attack is used to direct most of the aerodynamic
heating to the underside of the vehicle where the heat resistant
tiles give the greatest amount of protection.
At an altitude of approximately 30 miles, the orbiter makes a
series of maneuvers and S-turns to slow its speed. At 9.5 miles
in altitude and at a speed of Mach 1, the orbiter can be steered
using its rudder. The on-board computers fly the orbiter until it
goes subsonic (slower than the speed of sound: Mach 1). This happens
about 4 minutes before landing. At this time the commander takes
manual control of the orbiter and flies a wide arc approach. At
7.5 miles from the runway, the orbiter is flying about 424 miles
per hour at an altitude of 13,365 feet. About 2 miles from the runway,
the orbiter is flying at nearly 360 miles per hour on a glide slope
of 22 degrees.
Once lined up with the runway on approach, the orbiter continues
its steep glide slope of 18 - 20 degrees. The commander levels the
descent angle at a final glide slope of 1.5 degrees by performing
a "flare maneuver". The nose of the orbiter increases its pitch
(noses up) which slows its speed. The orbiter touches down at a
speed between 215-226 miles per hour. It is slowed and eventually
brought to a stop by the speed brake, wheel brakes and a drag chute.
It is this unique aerospace vehicle, a lifting body, that launches
like a rocket, orbits like a spacecraft and lands like a glider
that continues to link earth and space.
Student Worksheet
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