Launched in 1996-8, the Inmarsat-3s were built by Lockheed Martin Astro Space (now Lockheed Martin Missiles & Space) of the USA, responsible for the basic spacecraft, and the European Matra Marconi Space (now Astrium), which developed the communications payload.

The Inmarsat I-3 communications payload can generate a global beam and a maximum of seven spotbeams. The spotbeams are directed as required to make extra communications capacity available in areas where demand from users is high.

Inmarsat I-3 F1 was launched in 1996 to cover the Indian Ocean Region. Over the next two years F2 entered service over Atlantic Ocean Region-East, followed by F3 (Pacific Ocean Region), F4 (Atlantic Ocean Region-West) and F5 (limited services on a single spot beam, back-up and leased capacity).

Inmarsat I-3 F2 was launched without apogee kick motor, as the Proton-K Blok-DM1 launch vehicle was capable of direct GSO injection.

因为是地球同步卫星,东经64.5°的赤道上空，我之所以在前面说CNN请的专家只对了一半，是因为现在不知道 海事卫星-3 F1与赤道有没有偏移，如果有一点点，哪怕是半度，马航这条降落的弧线就要重画。至于马航失联客机的海事卫星天线当时对准海事卫星是40度角度应该没有问题，肯定在海事卫星的流水数据库里放着呢！最后是什么终端在向海事卫星发信号，乘客的游戏机？卫星电话？目前不知道！