Sea Launch Co. LLC officials today said the 72-hour countdown for the launch of the Space Systems/Loral-built Telstar 18 communications satellite will begin tonight. The satellite is scheduled for a June 28 launch on Sea Launch’s Zenit-3SL launch vehicle from the Odyssey Launch Platform located on the equator at 154 degrees West longitude. The launch window opens at 8:59 p.m. PDT. Telstar 18 carries 54 transponders (16 Ku-band and 38 C-band); it will be operated by Loral Skynet.