The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

194 inertia
inertia
The property of an object to resist changes to its state of
motion. Being an inherent property of mass, it is present
even in the absence of gravity. For example, although a
spacecraft may be located well away from any gravitating
mass, its inertia must still be overcome in order for it to
speed up, slow down, or change direction. Inertia is a
familiar concept in physics, but its origin is poorly understood.
It is believed to be a property of bodies primarily
due to their interaction with masses at the edges of the
universe. Momentum (mass times velocity) is a measure
of inertia; changes in momentum, resulting from the
action of an unbalanced force, permit a measure of inertial
mass.
inertia wheel
A rotating mass used to absorb minor torques (twisting
forces) created during the stabilization and control of a
spacecraft.
inertial force
(1) The force produced by the reaction of a body to an
accelerating force, equal in magnitude and opposite in
direction to the accelerating force. An inertial force lasts
only as long as the accelerating force does. (2) A force that
must be added to the equations of motion when Newton’s
laws are used in a rotating or an otherwise accelerating
frame of reference. It is sometimes described as a fictional
force because when the same motion is solved in the frame
of the external world, the inertial force does not appear.
inertial guidance
A type of guidance for a missile or a space vehicle implemented
by mechanisms that automatically adjust the
vehicle after launch to follow a given flight path. The
mechanisms measure inertial forces during periods of
acceleration, integrate the data obtained with previously
known position and velocity data, and signal the controls
to bring about changes needed in direction, altitude, and
so forth.
inertial platform
A gyro-stabilized reference platform that forms part of a
guidance system.
inertial reference frame
A frame of reference in which the first of Newton’s laws
of motion is valid. According to the special theory of
relativity, it is impossible to distinguish between such
frames by means of any internal measurement. For example,
if someone were to make measurements using a stopwatch
or a ruler inside a spaceship traveling at constant
high speed (even close to the speed of light) relative to
Earth, they would get exactly the same results as if the
ship were at rest relative to Earth.
inertial stabilization
A type of stabilization in which a spacecraft maintains a
fixed attitude along one or more axes relative to the stars.
inertial upper stage (IUS)
A two-stage solid-rocket motor used to boost heavy satellites
out of low Earth orbit into a higher orbit. It can be
used in conjunction with both the Space Shuttle and
Titan.
Inflatable Antenna Experiment (IAE)
A large antenna that was carried aboard the Space Shuttle,
deployed on the Spartan 207 platform, then inflated
in orbit. This experiment laid the groundwork for future
inflatable structures in space such as telescopes and satellite
antennas. IAE was developed by L’Garde of Tustin,
California, a small aerospace firm, under contract to JPL
(Jet Propulsion Laboratory). Once in low Earth orbit, the
Spartan served as a platform for the antenna, which,
when inflated, was about the size of a tennis court. First,
the IAE struts were inflated, followed by the reflector
canopy. High-resolution video photography recorded the
shape and the smoothness of the reflector surface over a
single orbit. Finally, the antenna was jettisoned from the
Spartan platform and disintegrated as it fell through the
atmosphere.
Shuttle deployment
Date: May 20, 1996
Mission: STS-77
Orbit: 180 km × 201 km × 39.1°
infrared
Electromagnetic radiation lying between the regions of
visible light and microwave radiation with wavelengths
of 0.75 to 1,000 microns. Very little of the infrared spectrum
from space reaches to sea level, although more of it
can be observed by high-altitude aircraft, such as SOFIA
(Stratospheric Observatory for Infrared Astronomy), or
telescopes on high mountaintops, such as the peak of
Mauna Kea in Hawaii. Most cosmic infrared is best studied
by infrared astronomy satellites. The near infrared
spans the shorter infrared wavelengths from 0.75 (just beyond
visible red) to 1.5 microns, the intermediate infrared
from 1.5 to 20 microns, and the far infrared from 20 to
1,000 microns (the start of the submillimeter band).
infrared astronomy satellites
In launch order, these are: IRAS (January 1983), Hubble
Space Telescope (April 1990), IRTS (March 1995), ISO