Photograph by Peter W. MerlinThe final countdown — Liftoff of a Delta II rocket from Vandenberg Air Force Base,Calif., on Sept. 15 marked the end of an era for a workhorse launch vehicle.
Liftoff of a Delta II rocket from Vandenberg Air Force Base, Calif., on Sept. 15 marked the end of an era for a workhorse launch vehicle and a significant leap forward for environmental science.
The booster — the last of its type — carried NASA’s Ice, Cloud and land Elevation Satellite-2 (ICESat-2), a state-of-the-art climate observation probe. The spacecraft is equipped with the most advanced laser instrument of its kind to measure the average annual changes in Earth’s polar ice sheets.
The ICESat-2 mission extends and improves upon a 15-year effort by NASA to monitor changes in polar ice that began in 2003 with the first ICESat mission. In addition, NASA scientists began collecting data in 2009 with Operation IceBridge, an airborne research campaign that monitors the accelerating rate of change in polar ice.
The ICESat-2 spacecraft was built to carry a single instrument called the Advanced Topographic Laser Altimeter System. A major technological leap, the ATLAS measures ice height by timing how long it takes individual light photons to travel from the spacecraft to Earth and back. Capturing 60,000 measurements every second, ATLAS will allow climate researchers to study ice surface elevation changes in unprecedented detail, discerning variations to within one centimeter. Using simple geometry, researchers will calculate volume from height and then convert volume into mass to determine how much ice is melting each year. Previous data revealed melting ice around the edges of Greenland and Antarctica, and the thinning of sea ice in the region. Annual runoff from hundreds of billions of tons of melting land and sea ice flows into the oceans, contributing to a worldwide rise in sea level.
“ICESat-2’s new observational technologies will advance our knowledge of how the ice sheets of Greenland and Antarctica contribute to sea level rise while also helping us understand the connection of sea ice loss to the global system,” said Thomas Wagner, cryosphere program scientist in NASA’s Science Mission Directorate.
In recent years, contributions from melting ice sheets in Antarctica and Greenland alone have raised global sea level by more than a millimeter a year, and the rate is increasing. ICESat-2 data will help researchers improve forecasts of future sea level changes and connect those changes to specific climate drivers. Polar ice sheets reflect some of the Sun’s heat back into space. When floating sea ice melts, it doesn’t change sea level but its loss exposes dark water that absorbs solar heat. This results in temperature changes that alter wind and ocean circulation patters, potentially affecting Earth’s global weather and climate.
“ATLAS required us to develop new technologies to get the measurements needed by scientists to advance the research,” said Doug McLennan, ICESat-2 project manager at NASA’s Goddard Space Flight Center, Greenbelt, Md. “That meant we had to engineer a satellite instrument that not only will collect incredibly precise data, but will collect more than 250 times as many height measurements as its predecessor.”
NASA illustrationAn artist’s impression of the ICESat-2 in orbit.
The ATLAS instrument was designed to measure not only ice, but also ocean and land surfaces including forests. Researchers can use the resulting data to estimate the amount of carbon stored in the world’s forests, study reservoir levels, or estimate tree density to improve forecasting of wildfires. Operators of oceangoing vessels can use ATLAS sea ice thickness measurements for navigation and forecasting.
The Delta II booster used to loft ICESat-2 was the last of its kind to be flown, ending a career that began in February 1989. Originally manufactured by McDonnell Douglas, which merged with Boeing in 1997, the Delta II had an excellent success rate. Out of 155 launches there was only one catastrophic failure and one partial failure that placed a satellite into a lower orbit than desired. The company retired the Delta II because it has been surpassed by new rocket technology and because some of the necessary components are no longer available.
Since December 2006, United Launch Alliance (ULA) — a joint venture between Lockheed Martin Space Systems and Boeing Defense, Space & Security — has provided launch services for the Delta II fleet. Following the ICESat-2 launch, ULA president and CEO Tory Bruno announced that enough spare parts remained in stock to assemble a Delta II “shell” for museum display. This construct will join a collection of historic launch vehicles in the Rocket Garden at NASA’s Kennedy Space Center Visitor Complex in Cape Canaveral, Fla.
“The Delta II rocket has been a venerable workhorse for NASA and civilian scientists, the U.S. military, and commercial clients throughout its almost 30 years of service,” said Bruno. “This program comes to a close with the final launch of NASA’s ICESat-2, but its legacy will continue and the Visitor Complex will help us keep the story of the success of this much-revered rocket in the hearts and minds of the public.”
