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GRAIL launch timeline
Posted: September 3, 2011

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Editor's note: The following times are based upon a launch during the first instantaneous liftoff opportunity available daily. If the launch slips to the second daily time, the rocket's second stage restart and payload deploy times will vary by a couple of minutes.

T-00:00 Liftoff
The ULA Delta 2 rocket's main engine and twin vernier steering thrusters are started moments before launch. The six ground-start strap-on solid rocket motors are ignited at T-0 to begin the mission.
T+01:17.1 Ground SRM Burnout
The six ground-start Alliant TechSystems-built solid rocket motors consume all their propellant and burn out.
T+01:19.0 Air-Lit SRM Ignition
The three remaining solid rocket motors strapped to the Delta 2 rocket's first stage are ignited.
T+01:20.5 Jettison Ground SRMs
The six spent ground-started solid rocket boosters are jettisoned in sets of three to fall into the Atlantic Ocean.
T+02:39.5 Jettison Air-Lit SRMs
Having burned out, the three spent air-started solid rocket boosters are jettisoned toward the Atlantic Ocean.
T+04:23.2 Main Engine Cutoff
After consuming its RP-1 fuel and liquid oxygen, the Rocketdyne RS-27A first stage main engine is shut down. The vernier engines cut off moments later.
T+04:31.2 Stage Separation
The Delta rocket's first stage is separated now, having completed its job. The spent stage will fall into the Atlantic Ocean.
T+04:36.7 Second Stage Ignition
With the stage jettisoned, the rocket's second stage takes over. The Aerojet AJ10-118K liquid-fueled engine ignites for the first of its two firings to boost the GRAIL satellites out of Earth orbit.
T+04:41.0 Jettison Payload Fairing
The 10-foot diameter payload fairing that protected the GRAIL spacecraft atop the Delta 2 during the atmospheric ascent is jettisoned is two halves.
T+07:09.7 Second Stage Cutoff 1
The second stage engine shuts down to complete its first firing of the launch after reaching a 90-nautical-mile circular orbit. The rocket and attached GRAIL spacecraft are now in a coast period before the second stage reignites.
T+67:56.7 Second Stage Restart
Delta's second stage engine reignites for the firing that accelerates the payload out of Earth orbit on the circuitous route to the Moon.
T+72:28.8 Second Stage Cutoff 2
The stage shuts down to complete its second burn after propelling GRAIL on the departure trajectory from Earth.
T+81:58.8 GRAIL-A Deploy
The first of the twin GRAIL spacecraft is released from the launch dispenser system atop the rocket's second stage.
T+90:13.8 GRAIL-B Deploy
NASA's second GRAIL spacecraft is released from the Delta 2-Heavy rocket to begin the journey from the Earth to the Moon to map the lunar gravity field.

Data source: ULA