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

HEAO-1
An X-ray astronomy satellite that surveyed the sky in the
0.2 keV to 10 MeV energy band, providing nearly constant
monitoring of X-ray sources near the ecliptic poles.
More detailed studies of a number of objects were made
through pointed observations lasting typically three to
six hours. The spacecraft remained active until January 9,
1979.
HEAO-2
The first fully imaging X-ray telescope to be placed in
orbit; later renamed the Einstein Observatory to honor
the centenary of the great physicist’s birth. Its angular resolution
of a few arcseconds, field-of-view of tens of
arcminutes, and sensitivity several hundred times greater
than any previous mission provided, for the first time,
the capability to create images of extended objects and
diffuse emission and to detect faint sources at such high
energies (0.2–4.5 keV). It revolutionized astronomers’
view of the X-ray sky. Observations ceased in April 1981.
HEAO-3
Like its predecessor HEAO-1, a survey mission operating
in the hard X-ray and gamma-ray (50 keV–10 MeV) band.
Its High Resolution Gamma-Ray Spectrometer Experiment,
built by JPL (Jet Propulsion Laboratory), was the
largest germanium spectrometer placed in orbit at that
time. The mission effectively ended when the cryogenic
coolant for the germanium detectors ran out in May
1981.
Launch
Vehicle: Atlas Centaur SLV-3D
Site: Cape Canaveral
heat barrier
The speed above which friction with an atmosphere may
damage a spacecraft. The heat barrier is of particular
importance during reentry. Special systems are needed to
cool the spacecraft when it goes beyond the heat-barrier
speed.
heat-shield
See reentry thermal protection.
HEAO Missions
Spacecraft Launch Date Orbit Mass (kg)
HEAO-1 Aug. 12, 1977 429 × 447 × 22.7° 2,720
HEAO-2 Nov. 12, 1978 526 × 548 × 23.5° 3,150
HEAO-3 Sep. 20, 1979 487 × 503 × 22.7° 3,150
heliopause 181
heavy-lift launch vehicle (HLV)
The most powerful type of space launch vehicle, sometimes
defined as one having the capacity to place payloads
of at least 10,000 kg into low Earth orbit or
payloads of 5,000 kg into geostationary transfer orbit.
Examples include the Space Shuttle, Atlas V, and Ariane
5.
helicon thruster
A device that works in a similar way to the pulsedplasma
thruster but with one important difference: a
traveling electromagnetic wave interacts with a current
sheet to maintain a strong force on a plasma moving
along an axis. This circumvents the pulsed-plasma
thruster’s problem of the force falling off as the current
loop gets larger. The traveling wave can be created in a
variety of ways, and a helical coil is often used.
heliocentric
Related to or having the Sun as its center.
heliopause
The boundary of the heliosphere, where the pressure
at the outer part of the heliosphere equals that of the
heliopause The heliopause and other structures shown
together with the exit trajectories of the twin Voyager and Pioneer
probes. NASA