Choose a configuration and delivery

H-IIA used two liquid-propellant core stages with solid boosters. The H-IIA 202 configuration had two large SRB-A boosters; 204 had four. Earlier 2022 and 2024 configurations also used smaller solid strap-on boosters. Those final digits describe hardware, not a count of serial core stages. A family name alone leaves out an important part of the launch specification.

More boosters are not automatically the best choice. Their performance must suit the destination, spacecraft mass and loads, while the full service must meet cost and operational requirements. A payload that fits one fairing or mounting interface cannot be assumed to fit another simply because both vehicles are called H-IIA.

A coast is a period of flight without the main engine firing. The vehicle continues along its trajectory under gravity, while attitude control, communications and thermal management may still be needed. Restart capability allows another burn at a different location along the orbit rather than forcing every velocity change into one continuous firing.

Flight 29 demonstrated an upgraded service in November 2015. Its upper stage supported a long coast and a third ignition near apogee, and Telstar 12 VANTAGE separated about four hours and twenty-seven minutes after liftoff. MHI and JAXA reported delivery closer to geostationary orbit than a conventional transfer orbit, not direct completion of the satellite’s final operational orbit.

A coast is part of a delivery sequence

An elliptical transfer orbit has a low point, perigee, and a high point, apogee. A spacecraft may need additional propulsion to reach its final orbit and change inclination. Giving it more useful initial conditions can reduce its remaining work, but that benefit depends on the actual orbit and spacecraft design.

In an original simplified comparison, one delivery leaves 1,500 metres per second of spacecraft velocity change to perform; another leaves 1,200. The reduction is 300 metres per second, or 20 percent of the first requirement. That does not mean a 20 percent reduction in propellant mass: the relationship also depends on engine efficiency and spacecraft mass. These numbers illustrate a comparison, not Telstar mission data.