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

ERM ended in January 1990 (due to failures of both
onboard tape recorders), more than three years of precise
altimetry data were available to the scientific community.
Launch
Date: March 13, 1985
Vehicle: Atlas E
Site: Vandenberg Air Force Base
Orbit: 775 × 779 km × 108.1°
Mass: 635 kg
geospace
The domain of Sun-Earth interactions, also known as the
solar-terrestrial environment. It consists of the particles,
fields, and radiation environment from the Sun to
Earth’s space plasma environment and upper atmosphere.
Geospace is considered to be the fourth physical
geosphere, after solid earth, oceans, and atmosphere.
geostationary orbit (GSO)
A direct, circular geosynchronous orbit at an altitude of
35,784 km that lies in the plane of Earth’s equator. A
satellite in this orbit always appears at the same position
in the sky, and its ground-track is a point. Such an
arrangement is ideal for some communication satellites
andmeteorological satellites, since it allows one satellite
to provide continuous coverage of a given area of Earth’s
surface.
geosynchronous orbit
A direct, circular, low-inclination orbit around Earth
having a period of 23 hours 56 minutes 4 seconds and a
corresponding altitude of 35,784 km (22,240 miles, or 6.6
Earth-radii). In such an orbit, a satellite maintains a position
above Earth that has the same longitude. However,
if the orbit’s inclination is not exactly zero, the satellite’s
ground-track describes a figure eight. In most cases, the
orbit is chosen to have a zero inclination, and stationkeeping
procedures are carried out so that the spacecraft
hangs motionless with respect to a point on the planet
GEOS Missions
geosynchronous/geostationary transfer orbit (GTO) 159
Spacecraft Date
Launch
Vehicle Site Orbit Mass (kg)
GEOS 1 Nov. 6, 1965 Delta E Cape Canaveral 1,114 × 2,273 km × 59.4° 175
GEOS 2 Jan. 11, 1968 Delta E Vandenberg 1,079 × 1,572 km × 105.8° 209
GEOS 3 Apr. 9, 1975 Delta 2918 Vandenberg 816 × 850 km × 115.0° 341
below. In this case, the orbit is said to be a geostationary
orbit.
geosynchronous/geostationary
transfer orbit (GTO)
An elliptical orbit, with an apogee(high point) of 35,784
km, a perigee (low point) of a few hundred kilometers,
and an inclination roughly equal to the latitude of the
launch site, into which a spacecraft is initially placed
before being transferred to a geosynchronous orbit
(GSO). After attaining GTO, the spacecraft’s apogee
kick motor is fired to circularize the orbit and thereby
achieve the desired final orbit. Typically, this burn will
also reduce the orbital inclination to 0° so that the final
orbit is not only geosynchronous but also geostationary.
Because the greater the initial inclination, the greater the
velocity change (delta ν) needed to remove this inclination,
it is important that launches of GSO satellites take
place as close to the equator as possible. For example, in
a Delta or an Atlas launch from Cape Canaveral, the
transfer orbit is inclined at 28.5° and the required delta
νincrement at apogee is 1,831 m/s; for an Ariane launch
from Guiana Space Centre, the inclination is 7° and the
deltaνis 1,502 m/s; while for a Zenit flight from the Sea
Launch platform on the equator, the delta ν is 1,478
m/s. By the rocket equation, assuming a (typical) specific
impulse of 300 seconds, the fraction of the separated
mass consumed by the propellant for the apogee
maneuver is 46% from Cape Canaveral, 40% from
Kourou, and 39% from the equator. As a rough guide,
the mass of a geostationary satellite at the start of its
operational life (in GSO) is about half its initial on-orbit
mass when separated from the launch vehicle (in GTO).
Before carrying out the apogee maneuver, the spacecraft
must be reoriented in the transfer orbit to face in the
proper direction for the thrust. This reorientation is
sometimes done by the launch vehicle at spacecraft separation;
otherwise, it must be carried out in a separate
maneuver by the spacecraft itself. In a launch from Cape
Canaveral, the angle through which the satellite must be
reoriented is about 132°.