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

Thagard, Norman E. (1943–)
An American astronaut and a veteran of five spaceflights
(including the first by an American on Soyuz) who, in
1994–1995, set a new U.S. space endurance record of 115
days during his stay aboard Mir (the previous record of
84 days having been held by the crew of Skylab 4). Thagard
received a B.S. (1965) and an M.S. (1966) in engineering
science from Florida State University and a
doctor of medicine degree from the University of Texas
Southwestern Medical School in 1977 and was on active
duty with the Marine Corps Reserve from 1966 to 1971,
rising to the rank of captain. Selected as an astronaut candidate
by NASA in 1978, he served as a mission specialist
on Shuttle flights STS-7 (1983), STS-51B (1985), and
STS-30 (1989), the payload commander on STS-42
(1992), and the cosmonaut/researcher on the Russian Mir
18 mission (1995).
THEMIS (Time History of Events and Macroscale
Interaction during Substorms)
A proposed mission to study the onset of magnetic
storms within the tail of Earth’s magnetosphere. It
would fly five microsatellite probes through different
regions of the magnetosphere and observe the origin and
evolution of storms. Led by Vassilis Angelopoulos of the
University of California, Berkeley, THEMIS is one of
four MIDEX (Medium-class Explorer) missions selected
by NASA in April 2002 for further development, two of
which will be selected for launch in 2007 and 2008.
thermal barrier
The speed at which frictional heat, generated by the rapid
passage of an object through the atmosphere, exceeds
endurance compatible with the function of the object.
thermal load
Stresses imposed upon a spacecraft or launch vehicle due
to expansion or contraction (or both) of certain structural
elements when exposed to a wide range of temperatures.
thermionic
Operating by means of electrically charged particles emitted
by an incandescent material.
thermodynamics
The study of the relationship between heat and mechanical
energy.
thermosphere
An upper part of Earth’s atmosphere that includes the
ionosphere and extends from an altitude of 85 km
(above the mesopause), where the temperature is about
−33°C, to the lower level of the exosphere at 500 km,
Thor 433
where the temperature is about 1,500°C. The thermosphere
is known to be very active with waves and vertical
tides of thin air far above the highest clouds and storms
of charged particles. However, it is still poorly understood
and is difficult to explore. Weather balloons and
research aircraft cannot reach it. Sounding rockets do
travel through the upper atmosphere—however, they can
at best take short snapshots of a specific region, and they
do not provide global mapping. Furthermore, the Space
Shuttle orbits in a region well above the lower thermosphere
and passes through it only briefly during reentry.
A promising alternative approach is to tether a probe
from a larger orbiting platform and then lower the probe
into the region of the thermosphere (see space tether).
The feasibility of this technique has already been demonstrated
by NASA’s SEDS experiments.
Thiel, Walter (1910–1943)
A German engineer who directed the development of the
V-2 (A-4) rocket motors (see “V” weapons). His designs
resulted in a leap from engines that developed a few
thousand kilograms of thrust to engines that were more
than ten times as powerful. Thiel and his family were
killed during the Allied attack on Peenemünde when
their shelter took a direct hit from a falling bomb.
Thor
An intermediate-range ballistic missile (IRBM) that was
adapted for use as a space launch vehicle and is the direct
ancestor of the Delta rocket family.
Development of the Thor was authorized in November
1955 to give the U.S. Air Force an independent
IRBM capability. At the time, the Army Ballistic Missile
Agency (ABMA) was already developing the Redstone
medium-range ballistic missile and the Jupiter IRBM.
Since the Air Force was now free to compete with the
Army in creating a similar weapon, an intense rivalry
broke out between the two services. The Air Force
requested proposals for a missile capable of carrying a
nuclear warhead at least 2,400 km—the distance from
England to Moscow. The Douglas Aircraft Company
came up with a design that used the warhead and guidance
system already being developed for the Atlas and
the engine from the Navaho. The resulting missile could
fit inside a Douglas C-124 Globemaster II for easy transportation
to a launch site. The first Thor was ready to fly
in August 1956, and the first operational Thors were
deployed in England by the end of 1958.
Two-thirds of the Thor’s body held the liquid propellants—liquid
oxygen and RP-1—for the missile’s singlestage
engine, whose thrust capability was similar to that
of both the Jupiter IRBM engine and each individual
Atlas ICBM booster stage engine. Two vernier engines,