Live Coverage Begins for STP-3

Hello, and welcome from NASA's Kennedy Space Center in Florida! A United Launch Alliance (ULA) Atlas V 551 rocket stands ready for liftoff at Launch Complex 41 on Cape Canaveral Space Force Station (CCSFS) for the U.S. Space Force's (USSF) Space Systems Command (SSC) Space Test Program 3 (STP-3) mission, which hosts NASA's Laser Communications Relay Demonstration (LCRD) and the NASA-U.S. Naval Research Laboratory Ultraviolet Spectro-Coronagraph (UVSC).

Launch is scheduled for 4:04 a.m. EST this morning, with a two-hour launch window. Follow along on NASA Television for the live broadcast.

Meteorologists with the U.S. Space Force 45th Weather Squadron predict a more than 90% chance of favorable weather for liftoff.

Here's a look at some of today's countdown and ascent milestones. All times are approximate:

COUNTDOWN 

Hr/Min/Sec Event

- 00:55:00 Start flight control final preparations to raise hydraulic pressures

- 00:45:00 Pressurize Main Engine Pneumatic System to flight pressure

- 00:16:00 Initiate fuel fill sequence

- 00:10:00 Weather briefing with Atlas Launch Weather Officer

- 00:05:00 Fuel fill sequence is complete; water deluge system actuation pressure adjustment is performed; Atlas L02 at flight level; Centaur L02 at Flight level; Centaur LH2 at flight level

- 00:04:00 Hazardous gas monitoring is complete; automatic computer sequencer takes control for all critical events through liftoff; Atlas first stage LO2 replenishment is secured, allowing the tank to be pressurized for flight

- 00:03:00 Atlas tanks reach flight pressure

- 00:02:00 Atlas first stage and Centaur upper stage switch to internal power; L02 and LH2 topping for Centaur will stop in 10 seconds

- 00:01:30 Launch control system is enabled

LAUNCH AND SPACECRAFT DEPLOYMENT

All Times Approximate

Hr/Min/Sec Event

00:00:00.1 RD-180 Engine Ignition

00:00:01.1 Liftoff of the Atlas V

00:00:03.9 Begin Pitch/Yaw Maneuver

00:00:34.7 Mach 1

00:00:48.7 Max Q (moment of peak mechanical stress on the rocket)

00:01:46.7 Solid rocket booster jettison

00:03:30.2 Payload fairing jettison

00:04:27.4 Atlas booster engine cutoff (BECO)

00:04:33.4 Atlas Centaur separation

00:04:43.3 Centaur first main engine start (MES-1)

00:10:38.4 Centaur first main engine cutoff (MECO-1) 

01:07:22.1 Centaur second main engine start (MES-2)

01:12:25.6 Centaur second main engine cutoff (MECO-2)

06:24:48.2 Centaur third main engine start (MES-3)

06:27:26.3 Centaur third main engine cutoff (MECO-3)

06:30:15.4 STPSat-6 Separation

07:10:02.4 LDPE-1 Separation

08:08:02.3 End of mission

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