Final Delta 2 rocket launches $1 billion ice probe

Ending a storied 30-year run as one of America's most successful rockets, United Launch Alliance's 155th and final Delta 2 roared to life for the last time Saturday and soared away from the California coast carrying a $1 billion NASA satellite to measure the thickness and extent of polar ice sheets, changes in sea level and the height of forest canopies and clouds.

The ICESat-2 satellite -- the acronym stands for Ice, Cloud and land Elevation Satellite 2 -- is the most sophisticated ice-monitoring spacecraft ever launched, equipped with advanced electronics and a laser that will fire 10,000 pulses per second at the ground below and then capture the faint reflections.

Timing the departure and arrival times of returning photons to within a billionth of a second, the satellite will be able to determine the thickness of ice below the spacecraft, giving scientists insights into how ice sheets change over time and how the loss of ice due to global warming and other factors might affect sea levels around the world.

The mission will build on the results of an earlier, less powerful ICESat mission and a more limited NASA aircraft campaign known as IceBridge, all aimed at monitoring the planet's ice inventory over decadal time scales.

"In the half a second it takes a person to blink, ICESat-2 will collect 5,000 elevation measurements in each of its six beams," said Tom Neumann, deputy project scientist for the ICESat-2 mission. "Every minute of every hour of every day for the next three years."

"And that incredible timing precision will allow us to measure elevation changes across the entire ice sheet to less than a centimeter," he said "And this is important, since an elevation change of just a centimeter over an ice sheet the size of Antarctica represents a tremendous amount of water, either gains to or loss from the ice sheet - 140 gigatons worth."

The Delta 2's RS-27A main engine thundered to life on time at 6:02 a.m. PDT (GMT-7; 9:02 a.m. EDT) followed by ignition of four strap-on solid-fuel boosters.

Launch was delayed 16 minutes by a minor technical glitch, but the final moments of the countdown went smoothly and the slender rocket quickly vaulted away from its firing stand at Vandenberg Air Force Base, Calif., arcing away to the south over the Pacific Ocean. The early moments of the flight appeared normal as the vehicle accelerated toward orbit.

The Delta 2 debuted in February 1989 when it launched the first operational Global Positioning System satellite from Cape Canaveral. Going into Saturday's flight, the boosters had chalked up 154 launches with only one outright failure in 1997, 100 flights ago.

"I'm a little bit melancholy about this," NASA Launch Director Tim Dunn said Thursday. "Delta 2 holds a really special place in so many folks' hearts.

Delta 2 rockets have launched scores of and satellite telephone relay stations, seven Mars missions -- including the Pathfinder, Spirit and Opportunity rovers -- Earth observation satellites, commercial payloads and trail-blazing NASA science probes, including the planet-hunting Kepler space telescope.

ICESat-2 was expected to be released into a 300-mile-high polar orbit about 52 minutes after launch.

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