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Gravity Probe-B launch timeline
Posted: April 17, 2004

T-00:00 Liftoff
The 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+01:04.0 Ground SRM Burnout
The six ground-start Alliant TechSystems-built solid rocket motors consume all their propellant and burn out.
T+01:05.5 Air-Lit SRM Ignition
The three remaining solid rocket motors strapped to the Delta 2 rocket's first stage are ignited.
T+01:26.0 Jettison Ground SRMs
The spent solid rocket boosters are jettisoned to fall into the Pacific Ocean. The spent casings remained attached until the vehicle passed into preset drop zone, clear of offshore oil platforms.
T+02:11.5 Jettison Air-Lit SRMs
Having burned out two seconds earlier, the three spent air-started solid rocket boosters are jettisoned toward the Pacific Ocean.
T+04:23.5 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+04:31.5 Stage Separation
The Delta rocket's first stage is separated now, having completed its job. The spent stage will fall into the Pacific Ocean.
T+04:37.0 Second Stage Ignition
With the stage jettisoned, the rocket's second stage takes over. The Aerojet AJ118-K liquid-fueled engine ignites for the first of two firings needed to place the Gravity Probe-B satellite into the proper orbit.
T+04:41.0 Jettison Payload Fairing
The 10-foot diameter payload fairing that protected the Gravity Probe-B satellite atop the Delta 2 during the atmospheric ascent is jettisoned is two halves.
T+11:15.6 Second Stage Cutoff 1
The second stage engine shuts down to complete its first firing of the launch. The rocket and attached Gravity Probe-B spacecraft are now in a long coast period before the second stage reignites. The orbit achieved should be 352 miles at apogee, 90 miles at perigee and inclined 90.014 degrees.
T+61:38.1 Second Stage Restart
Delta's second stage engine reignites for a short firing to raise the orbit's perigee.
T+61:54.3 Second Stage Cutoff 2
The second stage shuts down after a 40-second burst. The orbit achieved should be 356.2 miles at apogee, 344.1 miles at perigee and inclined 90.007 degrees.
T+66:50.0 Solar Array Deploy
The power-generating solar arrays on the Gravity Probe-B spacecraft are deployed in a process that will last about three minutes.
T+74:10.0 Begin Spin-up
The second stage begins a slow 0.1 rpm roll maneuver that is imparted into the satellite for its upcoming separation.
T+75:00.0 GP-B Separation
NASA's Gravity Probe-B spacecraft is released from the launch vehicle for its $700 million mission to test key aspects of Einstein's general theory of relativity.

Data source: Boeing.