Difference between revisions of "Synchronous orbit"

Revision as of 08:59, 28 July 2013

A stationary orbit is an orbit with the same orbital period as the rotational period of the orbited body. The eccentricity is equal to 0 and the inclination is exactly 0°. A satellite on this orbit will stay in the sky at the same position at all times, making the communication easy as the ground based telescopes don't have to follow the satellite's relative motion. The surface velocity is zero.

A stationary orbit is a special kind of synchronous orbit, which all have the same orbital period but may differ in inclination or eccentricity. Satellites on a synchronous but not stationary orbit have a ground track forming an analemma. Because it is impossible to get all values exact for a stationary orbit, every satellite on a synchronous orbit form an analemma.

Some celestial bodies don't allow synchronous orbits, and thus also no stationary orbits, because the altitude lies outside the celestial bodies' sphere of influence. This is because of a very slow rotation requiring a very high altitude to allow such long orbital periods explaining why all tidally locked moons don't have a synchronous orbits.

Kerbin

For Kerbin the orbital altitude is 2 868.75 km at an orbital speed of 1009.0 m/s.

Maneuver Planning

The basic maneuver plan for reaching this orbit is to first achieve a low energy orbit (LEO) and then perform two maneuvers to execute a Hohmann transfer. The first one called the periapsis maneuver is raising the apoapsis to the required altitude for a synchronous orbit. This places the spacecraft on a kerbisynchronous transfer orbit (KTO). The second one is at the apoapsis.

Depending on the required orbit the second burn also includes nearly all of the plane change to reduce the equatorial inclination to zero. For stationary orbits the periapsis maneuver should be executed when crossing the equatorial plane. Since the Kerbal Space Center is on the equator, the timing and trigonometry may be skipped.

The following are instantaneous impulse calculations for equatorial low energy orbits, and therefore the real maneuvers will always be somewhat more than these values.

For direct launches, transfers from the lowest orbits will be more efficient because they require less delta-v to reach from the surface of Kerbin. Higher LEOs may be preferable if the spacecraft is visiting a tug or space station and requires altitude above the atmosphere to execute a rendezvous. These maneuver plans may also be useful for one who wishes to boost a large space station assembled on LEO to KEO.

See also

• Geostationary orbit on Wikipedia
• Geosynchronous orbit on Wikipedia
• Synchronous orbit on Wikipedia