Booster ignition and liftoff of the United Launch Alliance Atlas V rocket to deliver the TDRS-M spacecraft to join the Tracking and Data Relay Satellite System, a critical communications link between ground stations and Earth-orbiting spacecraft including the International Space Station and Hubble Space Telescope.
The vehicle will pass Mach 1 about a minute after launch, followed by Max Q, the area of maximum dynamic pressure.
About four minutes into the flight, a series of key events occurs in rapid succession: Atlas booster engine cutoff, separation of the booster from the Centaur, ignition of the Centaur main engine for its first of two burns, then jettison of the payload fairing.