Sun Synchronous Polar Orbit



  1. Sun Synchronous Orbit Animation
  2. Sun Synchronous Polar Orbit Gif
  1. A polar orbit is one in which a satellite passes above or nearly above both poles of the body being orbited (usually a planet such as the Earth, but possibly another body such as the Moon or Sun) on each revolution. It therefore has an inclination of (or very close to) 90 degrees to the equator.
  2. A sun-synchronous orbit passes by any given point with the same local solar time, which is useful for consistent lighting and sun angle. Out of the three types of orbits (low, medium, and high Earth orbits), polar orbits often fall into low Earth orbits.
  3. A sun-synchronous orbit is an orbit around the Earth, where the movement of the satellite always looks the same when viewed from the Sun. A satellite in a sun-synchronous orbit still orbits the.
  4. Satellite Orbit Orbit Period 98.9 minutes Time of Day 10:30 am (Local) Example of a sun-synchronous polar orbit with an orbital altitude of 705 km above the Earth’s surface, an orbital peri-od of 98.9 minutes, resulting in 14.3 orbits per day, and an orbital inclination of 98.2° at the Equator.
Polar orbit and sun-synchronous orbit (sso)

With a suitable inclination, about 8 degrees off the polar orbit, that motion matches the slow motion of the Sun across the sky. If the satellite then starts near a noon-midnight orbit, it will always pass near noon and near midnight. A noon-midnight 'Sun-synchronous' orbit was actually used by some DMSP satellites.

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(Files in red–history)
Index
10a. Particle Drift
11. Explorers 1/3
11a. Geiger Counter
12. Rad. Belts
12H. Argus 1958
12a. Inner Belt
12b. Outer Belt
13. Fast Particles
14. Synch. Orbit
15. Energy
16. The Sun
16H. Schwabe, 1843
16a. Schwabe paper
16b. Carrington, 1859
17. The Corona
    The orbital period of a satellite increases as its mean distance from Earth grows. The space shuttle in a low altitude circular orbit, just above the atmosphere, completes one circuit in about 90 minutes. It orbits some 6700 km from the Earth's center, while the moon, at 380,000 km, completes one orbit in 27.3 days. Intermediate distances go with intermediate periods, and somewhere between those two extremes is a distance where the orbital period is 24 hours. It turns out to be at about 42,000 km or 26,000 miles, some 6.6 Earth radii.
      (More precisely, the period is 23 hours 56 minutes: 24 hours is the mean interval from noon to noon, but noon is determined by the Sun's position in the sky, and the Sun's position among the stars shifts slightly during that time.)

    [The formula for the period T of a satellite orbiting the Earth in a circle of radius R Earth radii can be derived from Kepler's 3rd law (see here for the details) and is (x here denotes multiplication)

    T = 84 minutesx Rx √R

    If you have a suitable calculator, you can easily check the value of T for R=6.6]

    A satellite orbiting above the equator at that distance keeps its position above the same spot on the ground; hence this is known as the synchronous orbit, from the Greek syn--same, chronos--time. Such an orbit is useful first and foremost for communication satellites, because a ground station linked to the satellite will always be in touch with it, as long as its antenna points to a fixed spot on the sky.

Sun Synchronous Polar OrbitPolar
Sun Synchronous Polar Orbit

The same holds for satellite dishes receiving TV broadcasts from such satellites, and of course, weather satellites designed to monitor (say) US weather will always have the proper view if parked in a synchronous orbit and facing the US. The NOAA agency of the US government ('National Oceanic and Atmospheric Administration') maintains in a set of GOES synchronous satellites to observe the weather and monitor the space environment. Images obtained by these satellites are available on the world wide web and are updated every 15 or 30 minutes.

NASA's tracking network, too, uses the TDRSS Satellites (Tracking, Data and Relay Satellite System) in synchronous orbit to collect data from near-Earth spacecraft. Currently more than 200 spacecraft share this orbit, most of them commercial communication satellites.

The synchronous orbit also happens to be the approximate boundary between the sheltered near-Earth magnetosphere and the outer portions where substorms and other active changes occur. For this reason many synchronous satellites have carried detectors for magnetic fields and for trapped or injected ions and electrons. Interest in that region is driven in part by the realization that the sudden arrival there of a large number of energetic particles, as happens now and then, can charge satellites to many hundreds of volts, can create false signals in their circuitry and can even, in extreme cases, cause serious damage.

(Above) The record of electrons intercepted by the synchronous satellite ATS 6 on 20 July 1974. The jagged peaks mark the arrival of electrons in substorms, and they gradually drift away again. The lower energies which persist belong to the plasma sheet of the magnetotail (described in a later section) in which the satellite is immersed for about half of its orbit.Questions from Users:
*** Synchronous satellites

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Sun Synchronous Orbit Animation

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    Author and Curator: Dr. David P. Stern
    Mail to Dr.Stern: education('at' symbol)phy6.org
    Co-author: Dr. Mauricio Peredo
    Spanish translation by J. Méndez

Sun Synchronous Polar Orbit Gif

Last updated 25 November 2001
Re-formatted 3-12-2006