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

186 HOPE (H-2 Orbital Plane)
instrumental in establishing Project Orbiter with von
Braun and others, resulting in the launch of Explorer 1,
the first American satellite.
HOPE (H-2 Orbital Plane)
A Japanese unmanned space plane that would be
launched by an H-2 booster and used to ferry materials to
and from the International Space Station. The project
has not yet progressed beyond the stage of flight-testing
subscale models.
Length: 16.5 m
Maximum diameter: 5.0 m
Mass
Total: 13,000 kg
Payload: 2,000 kg
Propellant: 1,000 kg
horizontal preflight checkout
A checkout accomplished with the vehicle in a horizontal
position, thereby reducing the requirements for
gantries, cranes, and similar items. Upon completion, the
vehicle is erected into vertical firing position. This kind
of testing is generally used with smaller vehicles and
spacecraft.
hot test
A propulsion system test that is carried out by actually
firing the propellants.
HOTOL (Horizontal Takeoff and Landing vehicle)
A British design, conceived by Alan Bond, for a singlestage-to-orbit
winged launch vehicle using a unique airbreathing
engine design. The RB545 air/liquid hydrogen/
liquid oxygen (LOX) engine was to be developed by Rolls-
Royce. Work on HOTOL began in 1982 by a Rolls-
Royce/British Aerospace team and had reached the stage
of detailed engine design and mockup when, in the mid-
1980s, the British government withdrew further funding.
HOTOL would have taken off horizontally with a rocketpropelled
trolley, switched to pure rocket propulsion at
Mach 5 or 6, ascended to orbit, and glided back to Earth
like the Space Shuttle to a runway landing. The HOTOL
airframe was derived from conventional vertical takeoff
rockets with the engines mounted at the rear of a blunt
based fuselage. Since such a vehicle’s empty center of
gravity is dominated by the location of the engine, the
wings and the tank for the dense LOX also had to be at the
rear. The payload bay and hydrogen tankage were placed
in a projecting forebody. The resulting configuration suffered
from a severe center of pressure/center of gravity
mismatch during the air breathing ascent. The center of
pressure shifted 10 m forward due to the wide Mach range,
the large fuselage cross-section-to-wing area ratio, and the
long overhang of the forward fuselage. Various design
changes were made to address these problems, all of which
eroded the payload. Conventional landing gear was
replaced by a specially designed takeoff trolley to improve
the marginal payload fraction. The final design had serious
operational disadvantages and a small payload, and the
only way the designers could continue to claim to put a
reasonable payload into orbit was by specifying untried
and speculative structural materials. HOTOL subsequently
evolved into Skylon, which is being developed by
Bond and his colleagues at Reaction Engines.
Length: 75.0 m
Core diameter: 7.0 m
Liftoff thrust (from 3 engines): 3,153,200 N
Mass: 250,000 kg (total), 50,000 kg (empty)
housekeeping
Routine tasks required to maintain spacecraft in habitable
and/or operational condition during flight.
Hubble Space Telescope (HST)
An orbiting observatory built and operated jointly by
NASA and ESA (European Space Agency), and named
for the American astronomer Edwin Hubble (1889–
1953). It has a 2.4-m-diameter main mirror and, following
upgrades and repairs since its launch, is equipped
with the Wide-Field and Planetary Camera 2 (WFPC-2),
the Near Infrared Camera and Multi-Object Spectrometer
(NICMOS), the Space Telescope Imaging Spectrograph
(STIS), and, most recently installed, the Advanced
Camera for Surveys (ACS).
During initial on-orbit checkout of Hubble’s systems, a
flaw in the telescope’s main reflective mirror was found
that prevented the proper focusing of incoming light—a
problem caused by the incorrect adjustment of a testing
device used while building the mirror. Fortunately, Hubble
was designed for regular on-orbit maintenance by the
Space Shuttle. The first servicing mission, STS-61 in December
1993, fully overcame the problem by installing a
corrective optics package and upgraded instruments. A second
servicing mission, STS-82 in February 1997, installed
two new instruments in the observatory, and a third, STS-
103 in December 1999, replaced Hubble’s six gyros. The
most recent Shuttle visit to Hubble, STS-109 in March
2002, was to install the ACS and refurbish the NICMOS.
The program includes significant participation by
ESA, which provided one of the science instruments, the