How Do Rockets Achieve Orbit?

Geosynchronous Orbit

• Geosynchronous orbit (GEO) is an orbit around Earth that is roughly one day in length. An object in geosynchronous orbit will appear to remain at the same longitude and to an earthbound observer will appear at the same point in the sky at the same time each day. In order to reach GEO, a rocket will need a speed of 26,400 miles per hour. Reaching this orbit is a two-step process. A rocket must first enter a geosynchronous transfer orbit (GTO), which is an elliptical orbit. The orbit is then circularized by the firing of the rocket's apogee motor.

Geostationary Orbit

• A geostationary orbit uses a GEO with an eccentricity of zero that is right on the equator or low enough that the craft can use propulsion to confine the movements of the craft. To an earthbound observer, an object in geostationary orbit appears to hang motionless in the sky. Any adjustments made or propulsion used to maintain the position is called station keeping.

Low Earth Orbit

• Low earth orbit (LEO) is an orbit that is only slightly above the planet. It can be 124 to 1,240 miles in altitude and can thought of as being about 1 percent of the distance to the moon. LEO is the lowest possible earth orbit, and to achieve it a rocket will need to travel 17,000 miles per hour. The orbit of a space shuttle is an example of LEO. It should be noted that because of the friction at this altitude these orbits decay rapidly and cannot be maintained for long periods of time.

Medium Earth Orbit

• A medium earth orbit or mid-earth orbit (MEO) is the orbit used most commonly by communication satellites and GPS nodes. In MEO it takes a craft half a day to orbit the planet. MEO falls between GEO and LEO.

Polar and Elliptical Orbits

• A polar orbit has a 90-degree inclination that is useful for mapping satellites as well as spy satellites. Achieving a polar orbit requires more energy because the rocket cannot take advantage of the free ride from Earth's rotation. Launches usually occur near the equator, where the rotational speed of Earth's surface is fastest. An elliptical orbit follows an elliptical as opposed to a circular pattern. The most common elliptical orbit is a sun-synchronous orbit, which is in line with a planet's own solar path. Maintaining such an orbit may require additional fuel as adjustments need to be made periodically to keep a craft in orbit.