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

184 high mass fraction
two Soft X-ray Imagers, which have 33-arcsecond resolution.
This gives astronomers precise locations of gammaray
bursts and allows detailed follow-up with optical
instruments on the ground. The Massachusetts Institute
of Technology operates the satellite, and the program is
managed by the Goddard Space Flight Center as an
Explorer Mission of Opportunity.
Launch
Date: October 9, 2000
Vehicle: Pegasus
Site: Kwajalein Missile Range, Marshall Islands
Orbit: 598 × 641 km × 1.9°
high mass fraction
A high value of the ratio of propellant mass to total
motor mass. Values of 0.9 and greater characterize highmass
fraction motors.
High Resolution X-ray Spectroscopy Mission
A mission that would provide an exciting new approach
to studying the origin of the chemical elements in stellar
nucleosynthesis as well as active galaxies and galaxy clusters.
It is identified in NASA’s Office of Space Science
Strategic Plan as a potential mission beyond 2007 but
remains in the early concept definition phase.
high-energy radiation
Penetrating particle or electromagnetic radiation with
energies of more than a few thousand electron volts. It
may include electrons, neutrons, protons, mesons, X-rays,
and gamma rays.
high-gain antenna (HGA)
A type of antenna used on board spacecraft to provide
high amplification of either transmitted or received radio
signals. HGAs typically consist of parabolic dishes and
must be accurately pointed to be useful.
Highwater
Two suborbital tests of the Saturn I launch vehicle that
resulted in the creation of massive ice clouds in the iono-
Highwater Missions
sphere. The second and third stages of the Saturn contained
87,000 liters of water to simulate the mass of fully
fueled stages. Following the successful launch of the first
stage, the rocket was detonated by explosives with a signal
from the ground. The released water formed a massive
cloud of ice particles several kilometers in diameter. By
this experiment, scientists had hoped to obtain data on
atmospheric physics, but poor telemetry made the results
questionable. Highwater 2 marked the third straight
launch success for the Saturn I and the first with maximum
mass on board. (See table, “Highwater Missions.”)
Himawari
See GMS (Geostationary Meteorological Satellite).
Hinotori
A Japanese satellite launched by ISAS (Institute of Space
and Astronautical Science) principally to investigate X-rays
from the Sun. It carried high-resolution soft (longer wavelength)
X-ray spectrometers and hard (shorter wavelength)
X-ray instruments that obtained the first images of solar
flares at energies above 25 keV and also observed celestial
X-ray bursts. Hinotori, whose name means “phoenix,” was
known before launch as Astro-A.
Launch
Date: February 21, 1981
Vehicle: M-3S
Site: Kagoshima
Orbit: 576 × 644 ×31°
Mass: 188 kg
Hipparcos
An ESA (European Space Agency) astrometry satellite for
measuring the position, brightness, and proper motion
(movement against the distant stellar background) of relatively
nearby stars to an unprecedented degree of accuracy.
Its name is an abbreviation of High Precision
Parallax Collecting Satellite and was chosen for its (somewhat
strained) similarity to that of the Greek astronomer
Hipparchus of Rhodes (190–120 B.C.). Although a faulty
launch put Hipparcos in a highly elliptical orbit instead of
Launch site: Cape Canaveral
Detonation
Spacecraft Date Altitude (km) Time after Launch Length of Experiment
Highwater 1 Apr. 25, 1962 105 2.5 min 1.62 days
Highwater 2 Nov. 16, 1962 167 4 min 53 sec 1.46 days