Mission Information

Taurus XL: Countdown 101
Illustration of a Taurus rocket

This graphic illustrates the configuration of the Taurus vehicle. Image credit: Orbital Sciences
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The four-stage Taurus XL rocket, built by Orbital Sciences Corp., is designed to be a versatile and dependable vehicle that can place a payload weighing up to 3,000 pounds into low-Earth orbit. It is a ground-launched version of the highly successful, air-launched Pegasus rocket.

You can share in the excitement of the live countdown via NASA TV or the Web. Coverage usually begins about two hours prior to liftoff. Below are some key events to watch for during a Taurus XL countdown. Keep in mind that these are only highlights, and event times and lengths may change from mission to mission.

Note: Times below begin in L-time, then changes to T-time when that clock starts. L-time is the absolute time remaining until scheduled liftoff. T-time includes built-in holds, in which the countdown clock pauses for a specified period of time.

L-3 hours, 20 minutes
  • Launch controllers check the communications between the control center, the range, and the launch control van near the pad
  • Spacecraft is verified ready for the launch countdown
L-2 hours, 50 minutes
  • Verify "T" clock and "L" clock are set correctly
  • Ensure tracking assets are ready to support the launch window
L-2 hours, 20 minutes/T-2 hours
  • Weather briefing
  • Start countdown clock at T-2 hours and counting
T-1 hour, 45 minutes
  • Clear launch site
T-1 hour, 25 minutes
  • Turn on avionics external power
  • Verify range is receiving closed-loop telemetry
T-1 hour, 15 minutes
  • Conduct telemetry and C-band tests
  • Conduct transient power test
  • Conduct avionics internal power test
T-55 minutes and holding
  • Built-in 15-minute hold
  • Launch team polled for readiness to proceed with the countdown
T-55 minutes and counting
  • Countdown resumes
  • Load navigation data into the Taurus flight computer
T-45 minutes
  • Weather and wind briefings
  • Verify flight hazard and caution areas are clear
T-25 minutes
  • Turn on external Flight Termination System power supply
T-20 minutes
  • Flight Termination System switched to internal power
T-12 minutes and holding
  • Built-in five-minute hold
  • Launch team is polled for readiness to switch spacecraft to internal power
T-12 minutes and counting
  • Countdown resumes
  • Verify spacecraft is ready for final launch configuration
  • Spacecraft switched to internal power
  • Avionics switched to internal power
  • Turn on S-band transmitters
  • Verify range is receiving open-loop telemetry
T-5 minutes
  • Final launch readiness poll
T-4 minutes, 30 seconds
  • Transient power is turned on
  • Safe-and-arm device armed
  • Flight computer navigation activated
T-1 minute
  • Auto sequence start
  • Liftoff of the Taurus XL rocket
NASA's John F. Kennedy Space Center