Firing the rocket engines at apogee then makes the orbit round. Satellites headed for GEO first go to an elliptical orbit with an apogee about 23,000 miles. These satellites orbit about 23,000 miles above the equator and complete one revolution around the Earth precisely every 24 hours. Satellites that seem to be attached to some location on Earth are in Geosynchronous Earth Orbit (GEO). One complete orbit in LEO takes about 90 minutes. This is where the Shuttle and ISS conduct their operations. LEO is the easiest orbit to get to and stay in. Low-Earth Orbit (LEO) is restricted to the first 100 to 200 miles of space. This is just a little less than full escape velocity. At an altitude of 242 kilometers (150 miles), this is about 17,000 miles per hour. Orbital velocity is the speed needed to stay in orbit. The escape velocity from the Earth is about 11.3 kilometers (7 miles) per second. The object's distance from the planet's center is also important. ![]() Each planet has a different escape velocity. Escape velocity depends on the mass of the planet. When these forces are balanced, the object is always falling into the planet, but because it's moving sideways fast enough, it never hits the planet.Įscape velocity is the speed an object must go to break free from a planet's gravity and enter into orbit. If momentum is too small, the object will be pulled into the other one and crash. If the forward momentum of one object is too great, it will speed past the other one and not enter into orbit. There is a constant tug-of-war between the satellites tendency to move in a straight line, or momentum, and the tug of gravity pulling it back.Īn object's momentum and the force of gravity have to be balanced for an orbit to happen. With gravity, it is pulled back toward the Earth. Without gravity, an Earth-orbiting satellite would go off into space along a straight line. This is Isaac Newton's First Law of Motion. The space station Skylab orbiting the Earth.Īn object in motion will stay in motion unless something pushes or pulls on it. The inclination is the angle the orbital plane makes when compared with the Earth's equator. The time it takes a satellite to make one full orbit is called its period. The closest point a satellite comes to the Earth is called its perigee. Sometimes they are closer, and at other times they are farther away. They are highly eccentric or "squashed." Satellites that orbit the Earth are not always the same distance from the Earth. The orbits of comets have a different shape. For the planets, the orbits are almost round. ![]() Orbits are elliptical in shape, this means they are similar to an oval. ![]() This imaginary surface is called the ecliptic plane. Most of the objects orbiting the Sun move along or close to an imaginary flat surface. In our solar system, the Earth and the eight other planets orbit the Sun. It can also be man-made, like the Space Shuttle or the ISS. A satellite can be natural, like the Earth or the Moon. An object in an orbit is called a satellite. And every time a rocket launches a payload, we hear the word "orbit." It's a widely used term, but do you know what an orbit really is?Īn orbit is a regular, repeating path that one object in space takes around another one. Every time the Space Shuttle meets up with the International Space Station (ISS), we hear it. Every time the Space Shuttle lifts off the launch pad, we hear it. Diagram of the planets and other heavenly bodies.
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