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

the intended geosynchronous one, its mission was ultimately
a triumph and resulted in two catalogues: the
Hipparcos catalogue of 118,000 stars with positions, parallaxes,
and proper motions measured to an unprecedented
accuracy of 2 milliarcseconds (see arcseconds),
and the Tycho catalogue of over a million stars with measurements
of somewhat lower accuracy. Its mission ended
in 1993 and its final catalogue was published in 1997.
Launch
Date: August 8, 1989
Vehicle: Ariane 44
Site: Kourou
Orbit: 542 × 35,836 km × 6.7°
Mass: 1,130 kg
Hiten
A Japanese lunar probe, launched by ISAS (Institute of
Space and Astronautical Science), that made multiple flybys
of the Moon from an extremely elliptical Earth orbit
and released Hagoromo, a smaller satellite, into lunar
orbit. Hiten itself was put into lunar orbit in February
1992 and crashed into the Moon on April 10, 1993. It
was the first lunar probe not launched by the United
States or Russia. Hiten, whose name means “celestial
maiden,” was known before launch as MUSES-A.
Launch
Date: January 24, 1990
Vehicle: M-3S
Site: Kagoshima
Orbit: 262 × 286,183 km × 30.6°
Mass: 185 kg
HNX (Heavy Nuclei Explorer)
A space laboratory for determining the properties of cosmic
rays. HNX would directly sample and measure the
properties of these high-speed subatomic particles using
silicon and glass detectors. It would be launched by the
Space Shuttle and be retrieved three years later. HNX has
been selected by NASA for study as a possible SMEX
(Small Explorer) mission.
Hohmann orbit
An elliptical trajectory, named after Walter Hohmann,
along which a spacecraft may move from one orbit to
another with the minimum expenditure of energy. Such
an orbit just touches the original and destination orbits,
and may be used for changing the orbit of an Earth satellite
or for sending a probe to another planet. It involves
two firings of the spacecraft’s engine: one to break out of
the original orbit and another to enter the destination
Hoover, George W. 185
orbit. Its chief disadvantage is that it requires relatively
long flight times. This can be overcome by judicious use
of gravity-assists.
Hohmann, Walter (1880–1945)
A German rocket engineer who was a prominent member
of the Verein für Raumschiffahrt (Society for Space
Travel) in the late 1920s. His book, Die Erreichbarkeit der
Himmelskörper (The Attainability of Celestial Bodies),
published in 1925, was so technically advanced that it
was consulted decades later by NASA when planning its
first interplanetary probes. In it, he describes his “power
tower” spacecraft, a huge cone-shaped rocket with an eggshaped
manned capsule at the top, and, more important,
the interplanetary transfer orbits that have been named
after him (see Hohmann orbit). He also wrote popular
works in the field of rocketry, as did his contemporaries
Willy Ley and Max Valier.
hold
A scheduled pause or unscheduled delay in the launching
sequence or countdown of a space vehicle or missile.
hold-down test
The testing of a system or subsystem in a launch vehicle
while the vehicle is restrained in a stand.
holding fixture
A device or equipment used to support and position the
upper launch vehicle stages and the spacecraft modules
during test, checkout, and handling operations.
holding pond
Also known as a skimming basin, a human-made basin
into which spilled propellants, deluge water, and washdown
water are drained from the launch pad, launcher
area, and launcher platform. The pond is so constructed
that the water can be drained and the propellants
skimmed for disposal.
Hoover, George W.
An early advocate of American satellite launches and an
instigator of Project Orbiter. Hoover entered the Navy in
1944 and became a pilot before moving to the Office of
Naval Research to conduct a program in all-weather flight
instrumentation. Later he helped develop the idea of
high-altitude balloons for use in a variety of projects.
These included Skyhook, which supported cosmic-ray
research and served as a research vehicle for obtaining
environmental data relevant to supersonic flight. In
1954, Hoover was project officer in the field of highspeed,
high-altitude flight, with involvement in the
Douglas D558 project leading to the X-15. He was also