Satellites bound for geostationary orbit (GEO), 35,786 km above the equator, can reach it in two ways: the rocket drops them in a geostationary transfer orbit (GTO) and the satellite completes the climb itself, or the rocket's upper stage delivers them directly into GEO. Only some launch vehicles offer direct GEO insertion, and the published performance figures show large differences.
GTO or direct GEO insertion?
In a GTO, the satellite still has to raise its lowest point and remove the orbital inclination with its own engine, which costs propellant and time. With direct insertion, the upper stage coasts to the highest point of the transfer orbit and fires again to circularise at GEO. This needs an upper stage that can coast for a long time and restart. ULA, for example, describes the Centaur upper stage of Atlas V as having demonstrated long-coast relight capability. As the published figures below show, direct insertion also reduces the payload mass the rocket can carry. Our guide to the geostationary transfer orbit explains the basics.
Published performance to GEO and GTO
- ULA Vulcan: according to ULA, up to 6,500 kg directly to GEO and 14,500 kg to GTO with six solid rocket boosters. With two boosters, the figures are 2,600 kg to GEO and 8,400 kg to GTO. The version without boosters is not offered for direct GEO. ULA also lists an upgraded configuration with 7,000 kg to GEO.
- ULA Atlas V: in its most powerful 551 configuration, according to ULA, 3,850 kg to GEO and 8,900 kg to GTO.
- Ariane 6: according to ESA, Ariane 64 with four boosters can launch approximately 11.5 tonnes into GTO and Ariane 62 approximately 4.5 tonnes. Its upper stage uses the reignitable Vinci engine, which allows it to reach a range of orbits on a single mission.
- SpaceX Falcon Heavy: according to SpaceX, up to 26,700 kg to GTO. SpaceX does not publish a figure for direct GEO insertion on its Falcon Heavy page.
The figures depend on the exact orbit definition. ULA defines GEO as 35,786 km circular at 0 degrees inclination and GTO as 35,786 km by 185 km at 27 degrees inclination.
What makes a launcher suited to GEO missions
- A restartable, long coast upper stage: essential for direct GEO insertion and for placing satellites in reduced inclination transfer orbits.
- Launch site latitude: launching near the equator, for example from Kourou in French Guiana, reduces the inclination the satellite has to remove.
- Performance margin: heavy launchers can trade payload mass for a better orbit, which saves propellant on the satellite and extends its life.
How to choose
The choice is a trade off. Direct GEO insertion saves propellant and time on the satellite, but the rocket can carry much less mass. A launch to GTO allows a heavier satellite on the same rocket, which then completes the climb with its own chemical or electric propulsion. Satellite mass, available propulsion and how quickly service has to start decide which option fits.
Frequently asked questions
Which rocket carries the most to GTO?
Of the vehicles compared here, Falcon Heavy has the highest published GTO figure, up to 26,700 kg according to SpaceX, followed by Vulcan with six boosters at 14,500 kg according to ULA.
Which launch vehicles can place satellites directly into GEO?
Among the vehicles with published figures, ULA lists direct GEO performance for Vulcan with boosters, up to 6,500 kg with six solid rocket boosters, and for Atlas V, up to 3,850 kg in the 551 configuration.
Why do most commercial satellites launch to GTO instead of GEO?
A rocket can carry considerably more mass to GTO than directly to GEO. Vulcan with six boosters, for example, is rated for 14,500 kg to GTO versus 6,500 kg to GEO according to ULA. The satellite then completes the climb with its own propulsion.
How much can Ariane 6 launch to GTO?
According to ESA, approximately 11.5 tonnes for Ariane 64 and approximately 4.5 tonnes for Ariane 62.
Related reading
- Geostationary Transfer Orbit (GTO) Explained
- Upper Stages and Kick Stages
- LEO, MEO and GEO Satellites Compared
Sources
Cover image: The first stage of an Atlas V 541 is lifted into position for the launch of NOAA's geostationary weather satellite GOES-T, 31 January 2022. Credit: NASA/Kim Shiflett (KSC-20220131-PH-KLS01_0020), public domain.