Even at apogee, the fuel needed to reduce inclination to zero can be significant, giving equatorial launch sites a substantial advantage over those at higher latitudes.
Russia's
Baikonur Cosmodrome in
Kazakhstan is at 46° north latitude.
Kennedy Space Center in the
United States is at 28.5° north.
China's
Wenchang is at 19.5° north.
India's
SDSC is at 13.7° north.
Guiana Space Centre, the European
Ariane and European-operated Russian
Soyuz launch facility, is at
5° north. The "indefinitely suspended"
Sea Launch launched from a floating platform directly on the equator in the
Pacific Ocean.
Expendable launchers generally reach GTO directly, but a spacecraft already in a low Earth orbit (
LEO) can enter GTO by firing a
rocket along its orbital direction to increase its velocity. This was done when geostationary spacecraft were launched from the
Space Shuttle; a "perigee kick motor" attached to the spacecraft ignited after the shuttle had released it and withdrawn to a safe distance. Although some launchers can take their payloads all the way to geostationary orbit, most end their missions by releasing their payloads into GTO. The spacecraft and its operator are then responsible for the maneuver into the final geostationary orbit. The 5-hour coast to first apogee can be longer than the battery lifetime of the launcher or spacecraft, and the maneuver is sometimes performed at a later apogee or split among multiple apogees. The solar power available on the spacecraft supports the mission after launcher separation. Also, many launchers now carry several satellites in each launch to reduce overall costs, and this practice simplifies the mission when the payloads may be destined for different orbital positions. Because of this practice, launcher capacity is usually quoted as spacecraft mass to GTO, and this number will be higher than the payload that could be delivered directly into GEO. For example, the capacity (adapter and spacecraft mass) of the
Delta IV Heavy is 14,200 kg to GTO, or 6,750 kg directly to geostationary orbit. If the maneuver from GTO to GEO is to be performed with a single impulse, as with a single solid-rocket motor, apogee must occur at an equatorial crossing and at synchronous orbit altitude. This implies an argument of perigee of either 0° or 180°. Because the argument of perigee is slowly perturbed by the
oblateness of the Earth, it is usually biased at launch so that it reaches the desired value at the appropriate time (for example, this is usually the sixth apogee on
Ariane 5 launches). If the GTO inclination is zero, as with
Sea Launch, then this does not apply. (It also would not apply to an impractical GTO inclined at 63.4°; see
Molniya orbit.) The preceding discussion has primarily focused on the case where the transfer between LEO and GEO is done with a single intermediate transfer orbit. More complicated trajectories are sometimes used. For example, the
Proton-M uses a set of three intermediate orbits, requiring five upper-stage rocket firings, to place a satellite into GEO from the high-inclination site of
Baikonur Cosmodrome, in
Kazakhstan. Because of Baikonur's high latitude and range safety considerations that block launches directly east, it requires less delta-v to transfer satellites to GEO by using a
supersynchronous transfer orbit where the apogee (and the maneuver to reduce the transfer orbit inclination) are at a higher altitude than 35,786 km, the geosynchronous altitude. Proton even offers to perform a supersynchronous apogee maneuver up to 15 hours after launch. The geostationary orbit is a special type of orbit around the Earth in which a satellite orbits the planet at the same rate as the Earth's rotation. This means that the satellite appears to remain stationary relative to a fixed point on the Earth's surface. The geostationary orbit is located at an altitude of approximately 35,786 kilometers (22,236 miles) above the Earth's equator. ==See also==