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

410 speed of sound
speed of sound
The speed at which small disturbances travel through a
medium. In the case of a gas, such as air, the speed of
sound is independent of pressure but varies with the
square root of temperature. Since temperature decreases
with increasing altitude in the atmosphere, so too does
the speed of sound; in air at 0°C, it is about 1,220 km/hr
(760 mph), though it also varies slightly with humidity.
The various regimes of flight are subsonic (well below the
speed of sound), transonic (near sonic speed), supersonic
(up to 5 times sonic speed), and hypersonic (above 5 times
sonic speed). Compressibility effects start to become
important in the transonic regime and very significant at
supersonic speeds, when shock waves are present. In the
hypersonic regime, the high energies involved have significant
effects on the air itself. The important parameter
in each of these situations is the Mach number—the
ratio of the speed of the object to the local speed of
sound.
Spektr
See Mir.
SPIDR (Spectroscopy and Photometry of the
Intergalactic Medium’s Diffuse Radiation)
A mission to map the web of hot gas that spans the universe.
Half of the normal matter in the nearby universe is
in filaments of hot gas, and SPIDR would observe it for
the first time. SPIDR’s data would answer fundamental
questions concerning the formation and evolution of
galaxies, clusters of galaxies, and other large structures in
Some Space Spin-offs
the universe. SPIDR has been selected by NASA for
study as a Small Explorer mission.
spin-off
A commercial or other non-space benefit derived from
space research. Some of the numerous devices and technologies
developed originally for use in spaceflight or
space science are listed in the table (“Some Space Spinoffs”).
spin stabilization
A simple and effective method of keeping a spacecraft
pointed in a certain direction. A spinning spacecraft
resists perturbing forces in the same way that a spinning
gyroscope or a top does. Also, because, in space, forces
that slow the rate of spin are negligible, once a spacecraft
is set spinning, the rate of rotation stays the same. With
a spinner, there are inherent inefficiencies because only
some of the solar cells are illuminated at any one instant
and because most of the radio wave energy, radiating
from the nondirectional antennas in all directions, is not
directed at Earth. Thrusters are fired to make desired
changes in the spin-stabilized attitude. They may require
complicated systems to de-spin antennas or optical
instruments that must be pointed at targets.
SPIRIT (Space Infrared Interferometric Telescope)
A highly sensitive orbiting observatory that would allow
the far infrared background to be resolved almost completely
into individual sources. SPIRIT is identified in
NASA’s Office of Space Science Strategic Plan as a poten-
Device/Technique Origin
Medical imaging Signal-processing techniques to clarify images from spacecraft
Bar coding NASA tracking system for spacecraft parts
Firefighter suits Fire-resistant fabric for use in spacesuits
Smoke detector Toxic vapor detectors aboard the Skylab space station
Sun tiger glasses Protective lenses for welders working on spacecraft
Car design software NASA software for use in spacecraft and airplane design
Cordless tools Portable, self-contained drills to enable Apollo astronauts to obtain moon samples
Fisher space pen Developed for use in space. Pressurized gas pushes the ink toward the ballpoint even in zero
gravity, while special ink works at temperature extremes
Invisible braces Translucent ceramic developed for use in spacecraft and aircraft
Joystick controller Control stick for the Apollo Lunar Rover
Scratch-resistant lenses Dual ion-beam bonding, in which a diamondlike coat is applied to plastic
Freeze-dried food Meals for early astronauts