5:54 a.m. PDT (1254 UTC)
We are just 8 minutes away from the final launch of a legendary rocket, the Delta II. All launch commit criteria are "go."
5:56 a.m. PDT (1256 UTC) -- GO for launch!
The ULA Launch Director Tom Heter has given the final approval to resume the countdown for flight of Delta II rocket to send NASA’s ICESat-2 into space. His concurrence was made following a readiness poll of the launch team by Launch Conductor Scott Barney that verified all systems are ready to proceed.
5:57 a.m. PDT (1257 UTC)
The ICESat-2 spacecraft has been declared configured for launch.
5:58 a.m. PDT (1258 UTC) -- Countdown resumes
T-minus 4 minutes and counting. The final phase of today's countdown is underway at Vandenberg Air Force Base in California to launch the last Delta II rocket and NASA’s ICESat-2 spacecraft to precisely measure Earth's ice sheets. The countdown clocks have resumed, leading us to a 6:02 a.m. PDT (9:02 a.m. EDT; 1302 UTC) liftoff.
In the next few seconds, the rocket stages will switch to internal battery power for launch and the pad’s water deluge system will be enabled. The water system will begin flowing at T-minus 60 seconds to suppress the sound intensity at launch.
5:59 a.m. PDT (1259 UTC)
T-minus 2 minutes, 30 seconds, Ordnance aboard the Delta II rocket is armed.
6:00 a.m. PDT (1300 UTC)
T-minus 2 minutes and counting. First stage liquid oxygen tank pressurization has begun. The rocket's vents are being closed so that the tank can be brought up to the proper pressure levels for liftoff. Occasional puffs of white vapor from the LOX tank will be seen through the remainder of the countdown from the center of the Delta II as the tank as the pressure stabilizes.
6:01 a.m. PDT (1301 UTC)
T-minus 55 seconds and counting. The Air Force’s Western Range at Vandenberg has confirmed its "green" condition for launch.
Coming up at T-minus 30 seconds, a final status check will be announced on Delta II and ICESat-2 readiness, followed by the solid rocket booster ignitors being armed at T-minus 11 seconds and the operator at the first stage console in the Launch Control Center manually sending the command to start the RS-27A main engine at T-minus 3 seconds.
6:02 a.m. PDT (1302 UTC)
LIFTOFF! Liftoff of the final Delta II, celebrating the rocket’s legacy by launching NASA's ICESat-2 to monitor Earth’s ever-changing environment. And the vehicle has cleared the tower!
6:02 a.m. PDT (1302 UTC)
T+plus 35 seconds. The Delta II rocket has broken the sound barrier as it accelerates to space on the combined power of its main engine and four strap-on solid motors. The vehicle is flying southward over the Pacific Ocean along a flight azimuth of 196 degrees.
6:03 a.m. PDT (1303 UTC)
T+plus 90 seconds. The four Northrop Grumman-made Graphite Epoxy Motors, or GEM-40s, have burned out and separated from the Delta II rocket. There were 1,003 GEM-40s launched on the Delta II program.
The RS-27A main engine continues to power the rocket into the predawn sky.
6:04 a.m. PDT (1304 UTC)
T+plus 2 minutes. Delta now weighs half of what it did at liftoff two minutes ago.
6:05 a.m. PDT (1305 UTC)
T+plus 3 minutes, 25 seconds. The Aerojet Rocketdyne first stage main engine has about one minute left to go in its burn. The engine is consuming kerosene fuel and liquid oxygen to produce more than 200,000 pounds of thrust.
6:06 a.m. PDT (1306 UTC)
T+plus 4 minutes, 45 seconds. Successful staging and ignition of the Delta II rocket’s second stage is confirmed.
The RS-27A main engine completed its burn and the first stage then separated, allowing the AJ10-118K upper stage engine to begin its first of two burns needed to inject the ICESat-2 spacecraft into the proper polar orbit during the launch.
This marks the 241st and final engine from the RS-27 family to be used by Delta.
6:07 a.m. PDT (1307 UTC)
T+plus 5 minutes, 5 seconds, The 10-foot-diameter, bi-sector composite payload fairing that protected ICESat-2 during ascent through the atmosphere has been jettisoned now that the rocket has ascended above the edge of space.
The Delta II rocket has shed 95 percent of its liftoff weight.
6:09 a.m. PDT (1309 UTC)
T+plus 7 minutes. The hypergolic second stage engine is burning well, consuming nitrogen tetroxide and a hydrazine blend called Aerozine 50 to reach a preliminary orbit around the Earth. The Aerojet Rocketdyne engine produces more than 9,700 pounds of thrust.
6:11 a.m. PDT (1311 UTC)
T+plus 9 minutes. The Delta II rocket remains on course as its Aerojet Rocketdyne second stage engine fires to put the vehicle and payload into orbit. Less than two minutes remain in this initial firing this morning.
6:13 a.m. PDT (1313 UTC)
T+plus 11 minutes, 5 seconds. The first cutoff of the second stage engine, known as SECO-1, has been confirmed. The Delta II rocket has arrived in an elliptical orbit around the Earth where it will coast for about 37 minutes before the engine ignites again to circularize the orbit.
6:16 a.m. PDT (1316 UTC)
T+plus 14 minutes. Data from the Delta II rocket has verified that the second stage achieved the desired orbit following SECO-1.
6:22 a.m. PDT (1322 UTC)
T+plus 20 minutes. The rocket's flight path is taking above the South Pacific, soon to fly over Antarctica and begin a north-bound trajectory. Deployment of ICESat-2 occurs over Madagascar.
6:32 a.m. PDT (1332 UTC)
T+plus 30 minutes. As the rocket coasts in this parking orbit, it performs a "BBQ roll" maneuver to keep the thermal conditions on the vehicle equal.
6:40 a.m. PDT (1340 UTC)
T+plus 38 minutes. We are 10 minutes away from the second stage engine restart. The upcoming circularization burn will last just 7 seconds, but will raise the current elliptical orbit to a near-circular orbit 288 statute miles above Earth, inclined at 92 degrees.
6:50 a.m. PDT (1350 UTC)
T+plus 48 minutes. The second burn of the Delta II rocket’s second stage has occurred to put the vehicle into a near-circular polar orbit. The ICESat-2 spacecraft will be deployed from the launch vehicle in approximately four minutes.
6:53 a.m. PDT (1353 UTC)
T+plus 51 minutes. A good orbit has been achieved by the second stage's second burn, telemetry confirms.
6:54 a.m. PDT (1354 UTC)
T+plus 52 minutes, 45 seconds. SPACECRAFT SEPARATION! NASA’s Ice, Cloud and land Elevation Satellite-2, or ICESat-2, has been released into space from the Delta II rocket's second stage, completing the primary objective of today's launch!
The spacecraft will act like a sophisticated stop-watch, firing its multi-beam laser-ranging instrument 10,000 times per second and measuring the time it takes for photons to reach the Earth’s surface and bounce back to the satellite with a billionth-of-a-second accuracy. That will enable the monitoring of ice elevation changes to the thickness of a No. 2 pencil.