VANDENBERG AIR FORCE BASE -- A heavy blanket of fog and a persistent drizzle couldn't dampen the joy surrounding this week's Delta 2 rocket launch that saw the return of a venerable booster and a comeback for the science team.

The Delta 2 rocket launches in fog. Credit: Walter Scriptunas II SEE MORE IMAGES

Lifting off in the middle of the night Wednesday from California's Central Coast, spectators three miles away heard but never could see the rocket ascending. The "marine layer" of stratus clouds and fog was making sure to keep the view hidden.

But it didn't matter.

It was the first time a United Launch Alliance Delta 2 rocket had flown in almost three years. The dependable little vehicle would soon get its 150th successful launch by deploying the Orbiting Carbon Observatory No. 2, the 228th primary payload to entrusted to the launcher in the past quarter-century.

"I do dearly love this rocket," said NASA launch director Tim Dunn.

"So when it appeared three years ago we had flown our final manifested mission with (the) NPP (weather satellite) from Vandenberg in the fall of 2011, it was a bit of a sad time for me.

"But I did know ULA had five whitetail Delta 2s that they had manufactured. I knew there was some hope for the future. Our agency did take advantage of those whitetails and have since procured four of them."

It's that kind of fond attachment that makes the Delta 2 a special rocket.

Workers and engineers clamored to get assigned to be part of the return to flight mission.

But the Delta 2 won't be around forever, making each remaining mission a step closer to a final emotional goodbye.

There's only three launches left on the schedule, with one additional rocket available for sale.

For the science team, Wednesday was sweet redemption.

They had seen their first OCO get destroyed in a Taurus XL rocket launch accident five years ago.

Yet the importance that the carbon dioxide sniffer data promises in the climate change debate meant NASA got approval to build another satellite and try again, albeit with a different launcher.

"It's been a long run up to the starting line of this race. But we are ready to start now," said David Crisp, the OCO 2 science team leader.

"It's absolutely fantastic to get another opportunity to actually do these incredibly important scientific measurements. It's been a long, hard road but boy I am glad to be back.

"We've done everything humanly possible...to ensure a safe and successful launch. In addition to that, the launch vehicle that we are riding this time -- the Delta 2 -- is the most reliable launch vehicle in NASA's fleet. I am honored that anybody would consider flying such a small small science experiment on such a highly reliable vehicle."

"I only had one requirement -- that was basically a safe, reliable ride into space," said Ralph Basilio, OCO 2 project manager with NASA's Jet Propulsion Laboratory in Pasadena, California, adding Delta delivered a "perfect ride."

At just 7 feet tall and 999 pounds, OCO 2 was a diminutive cargo to fly on the medium-class Delta 2. But the rocket's track record speaks for itself, having flown 50 times for NASA, all successfully.

"This challenging mission is both timely and important," said Michael Freilich, director of the Earth Science Division of NASA's Science Mission Directorate in Washington. "OCO 2 will produce exquisitely precise measurements of atmospheric carbon dioxide concentrations near Earth's surface, laying the foundation for informed policy decisions on how to adapt to and reduce future climate change.

OCO 2 will map the world in cycles every 16 days, collecting 8 million measurements each time to gauge the seasonal and yearly variables in carbon dioxide, the key greenhouse gas.

"Scientists currently don't know exactly where and how Earth's oceans and plants have absorbed more than half the carbon dioxide that human activities have emitted into our atmosphere since the beginning of the industrial era," said Crisp.

"Because of this we cannot predict precisely how these processes will operate in the future as climate changes. For society to better manage carbon dioxide levels in our atmosphere, we need to be able to measure the natural source and sink processes."

"Climate change is the challenge of our generation," said NASA Administrator Charles Bolden. "With OCO 2 and our existing fleet of satellites, NASA is uniquely qualified to take on the challenge of documenting and understanding these changes, predicting the ramifications, and sharing information about these changes for the benefit of society."

To get down to business, Delta released OCO 2 some 56 minutes after liftoff to begin its mission, which could last upwards of a decade.

"Delta 2 performed like a champ after almost three years," Dunn said. "There was pure joy in the mission director's center at spacecraft separation, I can tell you that!"