The semi-synchronous orbit is a near-circular orbit low eccentricity 26, kilometers from the center of the Earth about 20, kilometers above the surface. A satellite at this height takes 12 hours to complete an orbit.
As the satellite moves, the Earth rotates underneath it. In hours, the satellite crosses over the same two spots on the equator every day. This orbit is consistent and highly predictable. The second common medium Earth orbit is the Molniya orbit.
Invented by the Russians, the Molniya orbit works well for observing high latitudes. The Molniya orbit offers a useful alternative. The Molniya orbit is highly eccentric: the satellite moves in an extreme ellipse with the Earth close to one edge. As it moves away, its speed slows, so it spends more time at the top of its orbit farthest from the Earth. A satellite in a Molniya orbit takes 12 hours to complete its orbit, but it spends about two-thirds of that time over one hemisphere.
Like a semi-synchronous orbit, a satellite in the Molniya orbit passes over the same path every 24 hours. This type of orbit is useful for communications in the far north or south. Most scientific satellites and many weather satellites are in a nearly circular, low Earth orbit. Therefore, it has a relatively low inclination 35 degrees , staying near the equator.
In this highly inclined orbit, the satellite moves around the Earth from pole to pole, taking about 99 minutes to complete an orbit. During one half of the orbit, the satellite views the daytime side of the Earth. At the pole, satellite crosses over to the nighttime side of Earth. As the satellites orbit, the Earth turns underneath. By the time the satellite crosses back into daylight, it is over the region adjacent to the area seen in its last orbit.
In a hour period, polar orbiting satellites will view most of the Earth twice: once in daylight and once in darkness.
Just as the geosynchronous satellites have a sweet spot over the equator that lets them stay over one spot on Earth, the polar-orbiting satellites have a sweet spot that allows them to stay in one time. This orbit is a Sun-synchronous orbit, which means that whenever and wherever the satellite crosses the equator, the local solar time on the ground is always the same.
When the satellite comes around the Earth in its next overpass about 99 minutes later, it crosses over the equator in Ecuador or Colombia at about local time. Appears in these Collections Thinking About Teaching Collection Orbits and satellites - Physics narrative A Physics Narrative presents a storyline, showing a coherent path through a topic Other resources on Orbits Orbits Earth and Space. Demonstration: drawing diagrams of eclipses of the Sun and the Moon.
Orbits Earth and Space. Orbits can be explained by the Heliocentric Model of the Solar System. We've won an award! Learn more. Close Physics Links Explorer Explore the links between different physics concepts.
This has led to conflict between different countries wishing access to the same orbital slots countries near the same longitude but differing latitudes and radio frequencies. Limitations to usable life of geostationary satellites [1] When they run out of thruster fuel, the satellites are at the end of their service life as they are no longer able to keep in their allocated orbital position.
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