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

98 Dawn
preceded, in 2006, by SMART-2—a two-spacecraft array
to demonstrate the type of formation flying that is essential
to Darwin’s success. NASA is developing a similar
mission, the Terrestrial Planet Finder, and it is possible
that NASA and ESA will collaborate on a single mission
that they will launch and operate together.
Dawn
A future NASA mission to two of the largest asteroids in
the Solar System, Ceres and Vesta. Dawn, a Discovery
Program mission, is scheduled to launch in May 2006,
arrive at Vesta in 2010, orbit it for nine months, then
move on to Ceres in 2014 for a further nine-month
orbital stint. Dawn will be NASA’s first purely scientific
mission to use ion propulsion of the type known as XIPS
(xenon-ion propulsion system) that was flight-validated
by Deep Space 1. The probe’s suite of science instruments
will measure the exact mass, shape, and spin of
Vesta and Ceres from orbits 100 to 800 km high; record
their magnetization and composition; photograph their
surfaces; use gravity and magnetic data to determine the
size of any metallic core; and use infrared and gamma-ray
spectrometry to search for water-bearing minerals. Flybys
of more than a dozen other asteroids are planned along
the way. The overall goal of the mission is to learn more
about the early history of the Solar System and the mechanisms
by which the planets formed.
dawn rocket
A rocket launched into orbit in an easterly direction so
that Earth’s rotation augments the rocket’s velocity. Most
launches are of this type.
DE (Dynamics Explorer)
A NASA mission launched on August 3, 1981, involving
two spacecraft to study the interaction between the hot,
thin, convecting plasma of Earth’s magnetosphere and
the cooler, denser plasmas and gases in the ionosphere
and upper atmosphere. DE 1 and DE 2 were launched
together and placed in polar coplanar orbits to allow
simultaneous measurements at high and low altitudes in
the same field-line region. The spacecraft approximated a
short polygon 137 cm in diameter and 115 cm high. The
antennas in the x-y plane measured 200 m tip-to-tip, and
on the z-axis 9 m tip-to-tip. Two 6-m booms were provided
for remote measurements. Science operations continued
successfully over a nine-year period until they
were terminated on October 22, 1990. The spacecraft
were also known as Explorer 62 and 63.
De Laval, Gustav (1845–1913)
A Swedish engineer of French descent who, in trying to
develop a more efficient steam engine, designed a turbine
that was turned by jets of steam. The critical component—the
one in which heat energy of the hot highpressure
steam from the boiler was converted into kinetic
energy—was the nozzle from which the jet blew onto the
wheel. De Laval found that the most efficient conversion
occurred when the nozzle first narrowed, increasing the
speed of the jet to the speed of sound, and then
expanded again. Above the speed of sound (but not
below it), this expansion caused a further increase in the
speed of the jet and led to a very efficient conversion of
heat energy to motion. Nowadays, steam turbines are the
preferred power source of electric power stations and
large ships, although they usually have a different
design—to make best use of the fast steam jet, De Laval’s
turbine had to run at an impractically high speed. But for
rockets the De Laval nozzle was just what was needed.
De Laval nozzle
A device for efficiently converting the energy of a hot gas
to kinetic energy of motion, originally used in some
steam turbines and now used in practically all rockets. By
constricting the outflow of the gas until it reaches the
velocity of sound and then letting it expand again, an
extremely fast jet is produced.
Debus, Kurt H. (1908–1983)
An important member of Wernher von Braun’s V-2 (see
“V” weapons) development team who subsequently
supervised rocket launchings in the United States. Debus
earned a B.S. in mechanical engineering (1933), and an
M.S. (1935) and a Ph.D. (1939) in electrical engineering,
all from the Technical University of Darmstadt, before
being appointed an assistant professor there. During
World War II he became an experimental engineer at the
V-2 test stand at Peenemünde, rising to become superintendent
of the test stand and the test firing stand for the
rocket. In 1945, he came to the United States with a
group of engineers and scientists headed by von Braun.
From 1945 to 1950, the group worked at Fort Bliss, Texas,
and then moved to the Redstone Arsenal in Huntsville,
Alabama. From 1952 to 1960, Debus was chief of the
missile firing laboratory of the Army Ballistic Missile
Agency (ABMA). In this position, he was located at
Cape Canaveral, where he supervised the launching of
the first ballistic missile fired from there—an Army Redstone.
When ABMA became part of NASA, Debus continued
to supervise missile and space vehicle launchings,
first as director of the Launch Operations Center and
then of the Kennedy Space Center, as it was renamed in
December 1963. He retired from that position in 1974.
decay
See orbit decay.