It was ordered to replace the JCSAT-11 satellite which was lost in a launch failure on a Proton-M/Briz-M rocket in 2007, and is currently used as an on-orbit spare satellite; a role in which it replaced the older JCSAT-R spacecraft, providing a reserve for if one of the company's other satellites fails. It is a 4,000-kilogram (8,800 lb) satellite, which was constructed by Lockheed Martin based on the A2100AXsatellite bus, with the same configuration as JCSAT-10 and JCSAT-11.[2] The contract to build JCSAT-12 was awarded on 6 September 2007, the day after JCSAT-11 failed to reach orbit.[3]
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ). Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).