Design
| Enviro |
Astro | Propulsion
| Power | Thermal
| Structures | AD&C
| CDHS |
Test
Spacecraft
are put in specific orbits
to meet mission requirements
that
vary from maximum altitudes for imagery sensors
to communication satellite coverage areas. Each
orbit has its own unique set of design considerations,
which are related to the space
environment.
Orbits
LEO
(Low Earth Orbit) altitudes range from 90-600 nm.
Remote Earth sensing satellites use this orbit for
close proximity to the surface, which enhances their
sensor resolution.
Polar
orbits are a type of LEO that
have a characteristic 90 degree inclination. They
provide satellite sensors complete coverage of the
Earth's surface at least once per day.
Sun-synchronous
orbits are a type of LEO that have a characteristic
98 degree inclination. They provide satellite sensors
complete coverage of the Earth's surface at least
once per day. Furthermore, satellites can view the
same location at the same sun time every day.
MEO
(Medium Earth Orbit) altitudes range from 600-19,000
nm. They have a 12-hour period and are commonly
called semi-synchronous orbits. GPS constellation
is in a 10,900 nm semi-synchronous orbit.
HEO
(Highly Elliptical Earth Orbit) has a characteristic
63 degree inclination with 12-hour period. The apogee
is much higher over the northern hemisphere than
the perigee over the south, lending "hang time"
to satellite sensors observing north latitudes.
GEO
(Geosynchronous Earth Orbit)
altitudes
are 19,300 nm or greater with 24-hour period. Communication
satellites use this orbit for wide transponder coverage
and to remain over a specific region of the Earth.
Geostationary
orbits are a type of GEO with an inclination of
0 degrees, keeping a satellite fixed over the exact
same spot on Earth.
