As ICESat-2 set to open new era of Earth observation, era of Delta II poised to close
LOMPOC, Calif. – NASA and United Launch Alliance (ULA) are set to fly the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) atop a Delta II rocket from Space Launch Complex-2 at Vandenberg Air Force Base in California. Liftoff is scheduled to the opening of a 40-minute launch window at 5:46 a.m. PDT (8:46 a.m. EDT) on Sept. 15. The launch will be the final for ULA’s Delta II rocket, which first launched on February 14, 1989.
“This is the end of an era, as we prepare to launch the final Delta II rocket,” said Gary Wentz, ULA vice president of Government and Commercial Programs via a company-issued release. “This vehicle has truly created a legacy throughout its history launching NASA, critical U.S. military satellites and commercial clients.”
If everything goes as planned, ICESat-2 will provide precise measurements of the changing height of Earth’s glaciers, ice sheets and sea ice. ICESat-2 should be able to measure the average annual elevation change of ice sheets covering Greenland and Antarctica to within the width of a No. 2 pencil, capturing 60,000 measurements per second.
“The new observational technologies of ICESat-2 – a top recommendation of the scientific community in NASA’s first Earth science decadal survey – will advance our knowledge of how the ice sheets of Greenland and Antarctica contribute to sea level rise,” said Michael Freilich, director of the Earth Science Division in NASA’s Science Mission Directorate.
ICESat-2 will continue and improve on NASA’s monitoring of changes to polar ice heights, which began with the launch of the original ICESat in 2003 and continued in 2009 with Operation IceBridge, a research mission that observed yearly changes in the ice using airborne instruments.
ICESat-2 carries a single scientific instrument, the Advanced Laser Altimeter System (ATLAS), which measures height by timing how long it takes for individual photons of light to travel from the spacecraft to Earth and back.
“ATLAS required us to develop new technologies to get the measurements needed by scientists to advance the research,” said ICESat-2 project manager’s Doug McLennan. “That meant we had to engineer a satellite instrument that not only will collect incredibly precise data, but also will collect more than 250 times as many height measurements as its predecessor.”
ATLAS will fire its six beams of green light 10,000 times a second, sending hundreds of trillions of photons to the ground. ATLAS uses a beryllium telescope 2.6 feet (about 79 centimeters) in diameter to capture the returning photons. The roundtrip of individual photons to and from the Earth is timed to the billionth of a second to precisely measure elevation. The spacecraft’s location is precisely measured using GPS and star trackers.
With so many photons returning from its six beams, ICESat-2 will get a much more detailed view of the ice surface that its predecessor, ICESat. If both satellites were flown over the same football field, ICESat would take only two measurements, one in each end zone, but ICESat-2 would collect 130 measurements between the end zones.
ICESat-2 was designed and built by Northrop Grumman. The spacecraft utilizes Northrop Grumman’s LEOStar-3 satellite bus to provide power and orbit control for ATLAS, as well as propulsion, navigation, attitude control. thermal control, ground communications and more. The spacecraft measures 8.1 feet x 6.1 feet x 12.5 feet (2.5 meters x 1.9 meters x 3.8 meter) and weighs 3,338 pounds (1514 kilograms) with propellant.
The spacecraft’s four solar panels will deploy after launch, and should provide an average of 3,800 watts. The panels will charge ICESat-2’s lithium-ion battery.
ICESat-2 will launch atop a ULA Delta II 7420-10 rocket, which is being fielded to deliver the spacecraft into a 310 mile (499 kilometer), near-circular polar orbit. This will be the final launch of the Delta II, which has been used on more than 50 NASA missions, including the Mars rovers Spirit and Opportunity.
The launch vehicle’s payload faring (PLF) is a two-piece shell that is 10 feet (3 meters) in diameter and encapsulates the spacecraft to protect it from the launch environment during its ascent. The rocket’s height with the PLF is approximately 132 feet (40 meters).
The Delta II second stage is a hypergolic-fueled vehicle with corrosion-resistant stainless steel propellant tanks. It uses a single AJ10-118K rocket engine producing 9,850 pounds of thrust. The second stage’s guidance section provides structural support for the propellant tanks, the PLF mountings for vehicle electronics and the structural and electronic interfaces with the spacecraft.
The Delta II first stage is 8 feet ( approximately 2.5 meters) in diameter and about 87 feet ( 26.5 meters) in length. Propulsion for the first stage is provided by an RS-27A engine which burns RP-1 (highly purified kerosene) and liquid oxygen. The RS-27A is capable of delivering 200,000 pounds of thrust at sea level. Guidance and flight control for the first stage is provided by the second stage’s avionics systems.
The Delta II 7420-20 rocket uses four graphite epoxy motors (GEMs), which are approximately 40 inches (1 meter) in diameter and 42 feet (12.8 meters) in length. The GEMs are constructed of a graphite-epoxy composite and are jettisoned by structural thrusters.
In addition to the ICESat-2 spacecraft, this flight will also carry four CubeSats, which will launch from dispensers mounted on the Delta II’s second stage. The CubeSats were designed and built by UCLA, University of Central Florida, and Cal Poly. The small satellites will conduct research in space weather, charging electric potential and resulting discharge events on spacecraft and the damping behavior of tungsten powder in a zero-gravity environment.
Once in orbit, ICESat-2 will undergo a 60-day check-out period, where the spacecraft and ATLAS instrument will be tested to make sure everything is functioning properly. ICESat-2 has an expected design life of three years and enough propellant onboard to last seven years.
Video courtesy of NASA
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.