Satellite fundamentals

1. Some Satellite Basics
Low Earth Orbit (LEO):
Orbiting at an altitude
of 600-1,000 km.
11
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.
22
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’.