Transcript A closed path around which a planet or satellite travels.

AGI’s Introduction to Orbits
What Is an Orbit?
A closed path around which a planet or satellite travels.
Johannes Kepler
discovered (in 1600s)
that planets orbit in
ellipses, not circles.
Satellites (natural or
human-made) also orbit
Earth in elliptical
pattern.
-Elliptical orbits
remain fixed in
space and Earth
spins under a fixed
satellite orbit.
All Sorts of Orbits!
• Low Earth Orbit
(LEO)
• Polar Orbit
• Medium Earth Orbit
(MEO)
• Highly Elliptical Orbit
(HEO)
• Geostationary (GEO)
• Molniya Orbit (Moly)
Low Earth Orbit (LEO)
•LEOs orbit relatively close to the Earth (e.g., several
hundred kilometers, km) with no minimum altitude.
•LEO orbits are characterized by short orbital
periods.
•Roughly 90 minutes
•Many revolutions per day and limited swath
areas (area that a satellite can see)
• All staffed space missions except lunar missions
have been LEO.
•Many Earth-observing satellites are LEO orbits.
Geostationary (GEO)
What’s in a name?
A geostationary satellite stays in one spot with respect to the
Earth.
Achieved by placing
satellite at altitude
where orbital period
exactly equals one
day.
Orbit is about
22,300 miles above
Earth and inclination
is exactly zero
degrees.
GEO
There is only one
altitude above Earth
with an orbital
period of 24 hours
All geostationary
orbits are in a ring
around Earth
Ring is called the
geostationary belt
Geostationary belt
is a limited resource
GEO
A short lesson on Urban navigation
Q. How can you tell what direction is south if
you’re lost in the middle of urban United
States with no compass or GPS receiver?
A. Look for a building or house with a TV
satellite dish. Geostationary satellites can only
hover above the equator, therefore all
northern hemisphere dishes are
communicating with geostationary satellites
toward the south.
Molniya (“Moly”)
Geostationary satellites for Russian communications pose severe
challenges since a majority of its land mass is too far north for
geostationary belt satellites to see.
The solution was to create a type of orbit called a Molniya orbit.
It allows long-term communications over northern Russian land mass.
Molniya
Molniya ground trace differs from most conventional ground traces.
The image below clearly illustrates the satellite hang time over Russia.
Click to begin animation
Polar
Polar orbit has a 90
degree inclination
Satellite will eventually
pass over all of Earth
Polar orbit satellites can
gather information
about the entire Earth
E.g., weather satellites
Constellations
Single satellites are often
insufficient to perform a
mission
Groups of satellites in
various orbits work
together to accomplish
the mission
This grouping of
satellites is called a
constellation
E.g., GPS system
Orbital Pattern Animation
Now That You Know the Basics
Use your new understanding of orbits to answer these
questions.
• If Norway wanted to obtain satellite imagery for all
of its major urban areas, what type of orbit would
be appropriate?
• Could researchers at McMurdo Station in
Antarctica use geostationary satellites for
communications?
Answer These Questions
1. Planets orbit in circles. T / F
2. Name three types of orbits.
3. A geostationary satellite can orbit around the
moon. T / F
4. How long is the orbit period of a geostationary
satellite?
5. Molniya orbits are commonly used to view Russia.
T/F
6. A satellite in an equatorial orbit (inclination = 0)
will eventually pass over the entire Earth. T / F
Answer Key
1. Planets orbit in circles. T / F
2. Name three types of orbits.
Low Earth Orbit (LEO); Polar Orbit; Medium Earth Orbit (MEO);
Highly Elliptical Orbit (HEO); Geostationary (GEO); and Molniya Orbit (Moly)
3. A geostationary satellite can orbit around the
moon. T / F
4. How long is the orbit period of a geostationary
satellite 24 hours
5. Molniya orbits are commonly used to view Russia.
T/F
6. A satellite in an equatorial orbit (inclination = 0)
will eventually pass over the entire Earth. T / F