The document discusses various types of satellite orbits. It explains that low Earth orbit ranges from 600-1000 km from the Earth's surface. Satellites in these orbits circle the Earth every 90 minutes. Their orbits can be either ascending, moving south to north, or descending, moving north to south, when crossing the equator. Many Earth observation satellites use a sun-synchronous polar orbit, which keeps the satellite in the same position relative to the sun as it circles the Earth 16 times per day.

1. Some Satellite Basics
Low Earth Orbit (LEO):
Orbiting at an altitude
of 600-1,000 km.
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Path of Satellite

2. NASA Earth-Observing Satellites
Ascending Orbit:
The satellite is
moving South to
North when that
portion of the orbit
track crosses the
equator.
Low Earth Orbit:
Orbiting at an
altitude of 600-
1,000 km.
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Path of Satellite
Ascending Orbit:
The satellite is moving South to
North when that portion
of the orbit track crosses the equator.

3. NASA Earth-Observing Satellites
Ascending Orbit:
The satellite is moving
South to North when
that portion of the orbit
track crosses the
equator.
Descending Orbit:
The satellite is
moving North to
South when that
portion of the orbit
track crosses the
equator.
Low Earth Orbit:
Orbiting at an
altitude of 600-
1,000 km.
33
Descending Orbit:
The satellite is
moving North to
South when that
portion of the orbit
track crosses the
equator.

4. NASA Earth-Observing Satellites
Ascending Orbit:
The satellite is moving
South to North when
that portion of the orbit
track crosses the
equator.
Descending Orbit:
The satellite is moving
North to South when
that portion of the orbit
track crosses the
equator.
Low Earth Orbit:
Orbiting at an
altitude of 600-
1,000 km.
44
Ascending vs.
descending
orbits are like
night and day!

5. NASA Earth-Observing Satellites
Sun-Synchronous:
The satellite is
always in the same
relative position
between the Earth
and Sun.
Ascending Orbit:
The satellite is moving
South to North when
that portion of the orbit
track crosses the
equator.
Descending Orbit:
The satellite is moving
North to South when
that portion of the orbit
track crosses the
equator.
Low Earth Orbit:
Orbiting at an
altitude of 600-
1,000 km.
55

6. NASA Earth-Observing Satellites
Sun-Synchronous:
The satellite is always in
the same relative
position between the
Earth and Sun.
Ascending Orbit:
The satellite is moving
South to North when
that portion of the orbit
track crosses the
equator.
Period:
A typical polar, Sun-synchronous
LEO
satellite takes about
90 minutes to
completely circle the
Earth. This gives it
about 16 orbits per
day.
Descending Orbit:
The satellite is moving
North to South when
that portion of the orbit
track crosses the
equator.
Low Earth Orbit:
Orbiting at an
altitude of 600-
1,000 km.
66
Period:
A typical polar, Sun-synchronous
LEO satellite takes
about 90 minutes to completely
circle the Earth. This gives it
about 16 orbits per day.

7. NASA Earth-Observing Satellites
Equatorial-Crossing
Time:
The local apparent solar
time when the satellite
crosses the equator.
Example: Terra has an
equatorial crossing time
of 10:30 am, and is
called an “AM” or
morning satellite.
Sun-Synchronous:
The satellite is always in
the same relative
position between the
Earth and Sun.
Ascending Orbit:
The satellite is moving
South to North when
that portion of the orbit
track crosses the
equator.
Period:
A typical polar, Sun-synchronous
LEO
satellite takes about 90
minutes to completely
circle the Earth. This
gives it about 16
orbits per day.
Descending Orbit:
The satellite is moving
North to South when
that portion of the orbit
track crosses the
equator.
Low Earth Orbit:
Orbiting at an
altitude of 600-
1,000 km.
77

8. Satellite Inclination
High Inclination
or Polar Orbit
(near 90º)
virtually
complete global
coverage
88
Low Inclination
Orbit (often
near 57º--
Space Shuttle)
no polar
coverage
Equator
Inclination:
The position of the orbital plane
relative to the equator. For near-polar
orbits, typically about 97º.

9. SSuunn--SSyynncchhrroonnoouuss OOrrbbiitt ooff TTeerrrraa

10. AAqquuaa’’ss OOrrbbiitt
• Near-polar, sun-synchronous, orbiting the Earth every 98.8
minutes, crossing the equator going north (daytime ascending)
at 1:30 p.m. and going south at 1:30 a.m.
• The orbit track changes every day but will repeat on a 16 day
cycle. This is true for both Aqua and Terra.

11. Polar-Orbiting Satellite iinn LLooww EEaarrtthh OOrrbbiitt ((LLEEOO))
Example from Aqua

12. Daytime Orbits
Terra - Descending Aqua - Ascending
When looking at an image of a piece of the orbit the two sensors
will have opposite ‘tilts’.