NASA has boosted its future plans using the venerable Delta 2 rocket, announcing Friday it would buy a fourth vehicle for upcoming Earth science research projects.

A Delta 2 launches from Vandenberg. Credit: Justin Ray/Spaceflight Now

The United Launch Alliance vehicle has flown 151 times since debuting on Valentine's Day 1989 and amassed a reliability rating of 98.7 percent. The track record includes only one outright failure and a remarkable string of 96 consecutive successful launches since 1997.

But after the U.S. Air Force transitioned its launches of new Global Positioning System satellites to the Delta 4 and Atlas 5 rockets, the Delta 2 lost its anchor customer.

For a time, it appeared the Delta 2 would fade into history after carrying a climate and weather observatory into orbit for NASA in October 2011.

But NASA breathed new life into the rocket last July, purchasing three future flights from an inventory of five remaining Delta 2s.

Friday's news buys a fourth of the five, leaving the elements of just one unsold rocket remaining in the stockpile.

This latest deal will carry the agency's second Ice, Cloud and Land Elevation Satellite into orbit from Vandenberg Air Force Base in California. ICESat 2 is slated for liftoff from Space Launch Complex 2-West in July 2016.

A Delta 2 on SLC 2-West at Vandenberg. Credit: Justin Ray/Spaceflight Now

NASA's total cost to launch ICESat 2 is $96.6 million, including the rocket, payload processing, integrated services, telemetry relay fees, reimbursables and other launch support requirements.

"United Launch Alliance is honored that NASA has selected the Delta 2 to launch this critical science mission," said Jim Sponnick, ULA vice president of mission operations.

"The Delta 2 launch system continues to offer excellent reliability and value to our customers and we look forward to launching the ICESat 2 mission together with the NASA team."

NASA has used the Delta 2 rocket on 50 launches to date, most notably to send the Spirit and Opportunity rovers, the Odyssey orbiter and Phoenix lander to Mars, plus the Stardust and Genesis sample-return spacecraft, MESSENGER to orbit Mercury and the Spitzer infrared space telescope.

An aerial view of the Delta 2 soaring to space with ICESat 1 in 2003. Photo: NASA TV/Spaceflight Now

The deal announced last summer will begin launching in July 2014 with the replacement Orbiting Carbon Observatory, becoming NASA's environmental satellite dedicated to mapping atmospheric carbon dioxide and man's impact on Earth.

The Delta will insert the observatory into a 438-mile polar orbit to collect about 8 million measurements every 16 days to create maps showing global distribution of carbon dioxide.

Next will be SMAP, the Soil Moisture Active Passive satellite, set to launch in October 2014. Outfitted with a radiometer and synthetic aperture radar, the craft will orbit 423 miles above to Earth make global measurements of soil moisture to improve flood predictions and drought monitoring.

ICESat 2 follows in July 2016 to continue work begun by the program's original spacecraft, which has since been retired after a seven-year mission that monitored the melting Arctic polar ice cap. A Delta 2 launched ICESat 1 in 2003.

The Delta 2 will put ICESat 2 into a 373-mile polar orbit where the craft's multi-beam micropulse laser altimeter will provide precise global ice topography measurements of polar ice sheets and glaciers, study ice thickness and examine sea surface and vegetation heights.

Then comes JPSS 1, the first civilian weather observatory in the Joint Polar Satellite System launching in November 2016. The craft will be operated by NOAA in a 512-mile-high orbit to take the planet's pulse daily for global forecasting, providing the ingredients needed for long-term weather outlooks.