Flight 173 is the 29th Ariane 5 launch and the fourth in 2006. An ARIANE 5 ECA (Cryogenic Evolution type A), the most powerful version in the ARIANE 5 range, will be used for this flight.
This will be the 25th commercial mission for Ariane 5. Launcher 533, the 25th production phase Ariane 5, is the fourth of the 30 PA contract launchers, for which AIRBUS DEFENCE AND SPACE’s Space Transportation business unit is production prime contractor. 533 is consequently the second complete launcher to be delivered to Arianespace, integrated and checked out under AIRBUS DEFENCE AND SPACE responsibility in the Launcher Integration Building (BIL).
In a multi-payload configuration using the SYLDA 5 "C" (900 mm stretched) system and a long pattern fairing, the launcher is carrying two telecommunications satellites: DIRECTV 9S in the upper position and OPTUS D1 in the lower position, plus the Japanese experiment LDREX 2 on the ASAP5 structure.