Arianespace will be webcasting live the launch of the Ariane 5 ECA rocket with the Arabsat 5C satellite Wednesday morning (21 September 2011).
According to the email I received about the launch it will occur sometime between 9:38 p.m. to 11:02 p.m. U.T.C. on Tuesday 20 September 2011. That translates to 7.38 am – 9.02 am Wednesday 21 September 2011 for the Australian Eastern Standard Time zone (Queensland, New South Wales, Australian Capital Territory, Victoria and Tasmania).
