Complex sentence: On 17 December 2015 Arianespace and European Space Agency signed a contract for the JWST to be launched on October 2018 using an Ariane 5 ECA with a cryogenic upper stage from Arianespace's ELA-3 launch complex at European Spaceport located near Kourou, French Guiana.
Split into simpler sentences: On 17 December 2015 Arianespace and European Space Agency signed a contract for JWST launch onboard Ariane 5 in October 2018. The telescope will be launched with an Ariane 5 ECA with a cryogenic upper stage from Arianespace's ELA-3 launch complex at European Spaceport located near Kourou, French Guiana.