Some Major Orbit Types
Steven Dutch, Natural and Applied Sciences,University
of Wisconsin - Green Bay
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Latitude of View
Longitude of View
Time Step (min)
Show Ground Tracks
Show Satellite Motion
Types of Orbit
- Geostationary: Equatorial circular orbit. A satellite in this orbit keeps pace with Earth's rotation
and appears to remain stationary in the sky. An interesting factoid is that at the equinoxes, these satellites
have brief blackout periods when they are in line with the Sun.
- Molniya: From the Russian word for "lightning." 12-hour highly elliptical and inclined orbit. Because of the Earth's
size, geostationary satellites are not visible north of 55 degrees, which includes much of Russia. Molniya orbits fill
the gap. Their great eccentricity means they travel slowly at apogee, allowing long periods of contact. Three Molniya
satellites allow continuous coverage. The 12 hour period means there is one apogee period over Russia, another over
North America, making them also useful as spy satellites for both sides. The orbital inclination is 63.4 degrees, which
results in zero precession of the major axis of the orbit, so the apogee remains fixed above the northern hemisphere.
- Navstar: Navigation satellites travel in circular 12-hour orbits with 55 degree inclinations. There are
six orbital planes in use.
- Tundra: More interesting theoretically than practically. A highly eccentric 24 hour orbit with the magic 63.4 degree inclination
to prevent precession of the major axis of the orbit. Sirius satellite radio is the only current user of Tundra orbits
since Molniya orbits are nearly as practical and closer to Earth.
- Inclined Geosynchronous: Allows the user to experiment with other geosynchronous orbits. Details
like precession of the orbit plane and perigee are not shown.
- Sun - Synchronous: Circular, near polar and slightly retrograde orbits with inclinations of 90+ degrees.
Orbits are chosen so precession of the orbital plane matches the Earth's motion around the Sun. When a sun-synchronous
satellite passes southbound over the daylight side of the Earth, it is always late morning, optimum time for photography.
Early morning haze has typically burned off and afternoon cumulus has not built up. Orbits are also chosen to pass
over the same tracks at regular intervals, generally 2-3 weeks. Sun-Synchronous orbits are used by most Earth observation
systems like Landsat.
- ISS (Space Station): Circular orbit with 51.6 degree inclination. Nominally the altitude is 350 kilometers,
but the station is a big sucker and
atmospheric drag causes the station to spiral in and require periodic boosts to maintain altitude. Actual altitude
is 300 to 400 kilometers.
- User-Defined Orbits: Up to three orbits can be custom designed. If
you want to show multiple Molniya or Navstar orbits, for example, you can create
- Latitude of View: Input the latitude of your
viewpoint. 90 is north polar, 0 is equatorial, -90 is south polar.
- Longitude of View: Input the longitude of your
viewpoint. West longitude is negative, east is positive. Applies to
drawing static views, although the box will display the current
longitude when the earth is rotating.
- Auto-Scale: Selects optimum scale for the selected orbits. Note, this doesn't
take viewing angle into account, only the maximum size of the orbit. So if, for example, you look
at a Molniya orbit from a latitude of 63.4 degrees (end-on), this option will probably not give
the best scale.
- Scale (km/px): Input the scale in kilometers per pixel. For low orbits
a scale of 25 km per pixel is suitable, for geosyncronous orbits a scale
of 200 is necessary to show the entire orbit.
- Time Step (min): Input the time step in minutes for
animations. For low orbits a step of 2-5 minutes is best, otherwise
satellites flick by too quickly to see. For geosynchronous orbits, 15-20
minutes is acceptable.
- Show Ground Tracks: Shows the sub-satellite point on
the ground as well as the radius to the satellite.
- Show Satellite Motion: Shows the actual motion of a
- Draw: Draws a static picture of the earth centered
on the chosen latitude and longitude, with selected orbits, satellites
and ground positions. No motion.
- Animate: Shows a moving view, with earth
rotation and satellite motions.
- Halt: Stop the animation temporarily. Pressing
Animate will restart it.
- ClearFigure: Erase the picture.
- Orbit: Check the box to select the desired orbit.
- Perigee-Apogee: Perigee is the closest point, apogee
is the most distant. Distances are km above the Earth's surface. Perigee
= (Mean Radius)(1-Eccentricity)-6371. Apogee = (Mean
- Mean Radius km: Average distance in kilometers from
the center of the earth. Also equal to half the length of the long axis
of the orbit (semi-major axis). Equal to 6371 + (Apogee+Perigee)/2
- Inclination: Inclination of the orbit plane with
resect to the equator. 0 is equatorial, 90 is polar, inclinations
greater than 90 are retrograde (opposite the earth's rotation). For a
true view of an orbit, select a latitude equal to 90-Inclination (26.6
- Node: Where the orbit crosses the earth's equatorial
plane. On this page, it defines the orientation of the orbit relative to
the line of sight. A node of zero means we are looking at the orbit
straight on, and 90 means we are looking at the orbit edge on.
- Eccentricity: How elliptical the orbit is. Most
orbits are nearly circular but Molniya and Tundra orbits are highly
elliptical. The eccentricity of the Molniya orbit, 0.741, means the
center of the earth is 0.741 of the way along the major axis from the
center of the ellipse to the end.
- Perigee Angle: The azimuth of the perigee measured
in the plane of the orbit. 0 means the perigee is at the equator. The
-90 values for the Tundra and Molniya orbits mean the perigee is in the
Southern Hemisphere, so the out of view period is short.
- User-Defined Orbits: Users can input their own
values for orbital parameters. If Perigee and Apogee are input, the
values for Mean Radius and Eccentricity will be adjusted. If Mean Radius
and Eccentricity are selected, the values for Perigee and Apogee will be
adjusted. Perigees below 200 km will result in short-lived satellites
due to atmospheric friction and of course perigees below zero will
intersect the earth.
Some Things to Do
- Show the sub-satellite position of a geostationary satellite. Note that it does remain fixed on the earth.
- Compare the motions of Geostationary, Tundra, and Inclined Geosynchronous orbits.
- Compare the motions of Geostationary, Molniya, and Navstar orbits.
- Create three user-defined orbits differing by a couple of hundred kilometers in radius. Note how the inner
satellite moves fastest.
- View Molniya and Tundra orbits from latitude 63 degrees (end-on). Note that auto-scale gives poor results here
because you only see the narrow axis of the orbits. Note how the sub-satellite point travels slowly across the
Northern hemisphere. Note how quickly the satellite whips through perigee in the Southern Hemisphere.
Return to Professor Dutch's Home Page
Created 14 February 2012, Last Update
02 April 2012
Not an official UW Green Bay site