Workhorse Delta II Stands Ready at Vandenberg for Final Launch on Saturday

The Delta II has a long and chequered history, extending back almost three decades. Its final launch is slated for this weekend from Vandenberg AFB with NASA’s ICESAT 2. Photo Credit: Mike Killian / AmericaSpace

If all goes well in the small hours of Saturday, 15 September, the workhorse Delta II—a rocket already used 154 times in almost three decades, with a near-perfect success record—will log its swansong mission to deliver NASA’s Ice, Cloud and Land Elevation Satellite (ICESat)-2 into a near-circular, near-polar orbit, some 287 miles (463 km) above Earth. Liftoff is targeted for 5:46 a.m. PDT (8:46 a.m. EDT) from Space Launch Complex (SLC)-2W at Vandenberg Air Force Base, Calif. And if the venerable old booster performs its job to its usual standards, it will proudly retire into the annals of space history with an unbroken run of 100 consecutive launch successes. Truly, the story of the Delta II is the story of the one of the most remarkable vehicles ever used to launch missions into space.

Primary payload for Saturday’s mission is ICESat-2, part of NASA’s Earth Observing System (EOS) and devoted to measurements of ice-sheet mass balance, land topography—including cities, lakes and reservoirs—and vegetation-canopy characteristics on a global scale. During its minimum three-year mission, the spacecraft will investigate how melting polar ice-sheets contribute to sea-level change and climate change. ICESat-2 data will also estimate sea-ice thickness to examine the exchange of energy, mass and moisture between the ice, ocean and atmosphere and measure vegetation canopies worldwide as part of efforts to shed new light on large-scale biomass change.

 

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As its name implies, this is the second mission of its kind, following on the heels of the hugely successful ICESat, which was launched in January 2003—also aboard a Delta II—and finally decommissioned and deorbited in 2010. ICESat examined the Home Planet’s polar regions with a Geoscience Laser Altimeter System (GLAS) and its data revealed important insights into ice loss from the Greenland and Antarctic ice-sheets, polar sea-ice thickness, vegetation canopy heights and cloud/aerosol altitudes in the atmosphere. ICESat results enabled the detection of a network of lakes beneath Antarctica and validated the rapid thinning of Arctic Ocean ice, a worrying effect of climatic change. However, after several months of technical troubles, GLAS was declared failed in February 2010, ending formal science operations, but ICESat remained in use for a few months of engineering tests, prior to being deorbited in August.

The Delta II has a long and chequered history, extending back almost three decades. Photo Credit: Mike Killian / AmericaSpace

By this time, however, ICESat-2 development was already underway, with initial hopes that it would be ready for launch in 2015. However, the mission suffered numerous technical troubles with its single scientific instrument—the Advanced Topographic Laser Altimeter System (ATLAS), provided by NASA’s Goddard Space Flight Center (GSFC) in Greenbelt, Md.—and the launch date corresponding slipped to the right, firstly into late 2016, then mid-2017 and finally September 2018. In order to maintain data continuity during the multi-year period between the demise of ICESat and the arrival of ICESat-2, NASA’s Operation IceBridge has utilized a DC-8 aircraft flying out of Thule, Greenland, and Punta Arenas, Chile, to maintain annual observations of the ice sheets and sea ice in the northern and southern hemispheres. Laden with radar instruments, laser altimeters and mapping gear, IceBridge permitted scientists to gain three-dimensional perspectives of Arctic and Antarctic ice, with specific attention being paid to Pine Island Glacier, whose rapid stage of melting is directly responsible for 25 percent of Antarctica’s ice-mass loss.

ICESat-2’s ATLAS instrument is a space-based lidar and beryllium telescope which will emit visible laser pulses at 532 nanometers, generating six beams in three pairs—each pair some 2 miles (3.3 km) apart—to determine surface-slope and provide greater ground coverage. The instrument will take elevation measurements every 27.5 inches (70 cm) along ICESat-2’s ground-track. Fabrication of ATLAS got underway in March 2014 and early the following year the instrument underwent a punishing series of vacuum-chamber tests to validate not only the performance of its detectors and electronics, but also of the ground-based computer programs which will receive its data and interpret them.

The Delta II dedicated to the ICESat-2 mission is assembled at SLC-2W. Photo Credit: ULA

Although ICESat-2 evolved as an Orbital Sciences Corp. project, the company subsequently merged with Alliant TechSystems to form Orbital ATK in early 2015, before being acquired by Northrop Grumman in a purchase concluded in June 2018. The spacecraft was transported by truck from Northrop Grumman’s facility in Gilbert, Ariz., to Vandenberg, on 12 June 2018, whereupon it was uncrated and moved to the Astrotech Space Operations Facility for pre-flight processing. Physically, ICESat-2 is based upon the LEOStar-3 “bus”—originally produced by Orbital Sciences Corp.—and weighs about 3,340 pounds (1,500 kg). Later in June, ICESat-2 engineers at Vandenberg successfully completed the final ground-based tests of the ATLAS lasers.

In addition to the importance of the ICESat-2 mission itself, Saturday’s flight is notable as the final outing of the Delta II, a booster which has already launched 154 times since 14 February 1989 and is one of the world’s most reliable rockets. During its long and illustrious career, it has lofted payloads for communications, national security, science and planetary and deep-space exploration. In its earliest incarnation, it was built by McDonnell Douglas and, most recently, by United Launch Alliance (ULA), which was formed in December 2006. In the immediate aftermath of the January 1986 Challenger tragedy, plans to gradually phase out U.S. expendable launch vehicles in favor of the shuttle were abandoned and the highly reliable Delta was brought back into production as the Delta II.

MESSENGER launches towards Mercury aboard a Delta II rocket, in August 2004. Image Credit: NASA

Its inaugural launch on Valentine’s Day in 1989 boosted a Global Positioning System (GPS) Navstar into orbit and over the next two decades it sent seven orbiters and landers to Mars, including the two rovers, Spirit and Opportunity, in the summer of 2003. The Delta II also launched the Near-Earth Asteroid Rendezvous (NEAR) in February 1996, the Genesis solar-wind sample-return spacecraft in August 2001, the ill-fated Comet Nucleus Tour (CONTOUR) in July 2002, the Spitzer Space Telescope in August 2003, the Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) mission to Mercury in August 2004, Deep Impact in January 2005, Dawn in September 2007 and Kepler in March 2009.

In spite of a partial failure to deploy KoreaSat-1 into orbit in August 1995, due to the failure of one of its Solid Rocket Motors (SRMs) to separate properly, and a catastrophic explosion, just 13 seconds after liftoff, on its 55th flight in January 1997, which destroyed the first GPS Block IIR satellite, the Delta II can boast a virtually unblemished service record, as explored in additional depth by this previous AmericaSpace article. Its success rate hovers at 99.3 percent and its flight rate peaked at 12 flight in a single year in 1998. The Delta II logged its 100th launch in 2001 and if Saturday’s flight of ICESat-2 goes well, it will mark a consecutive run of 100 successful flights. Original plans called for it to phased out of service in 2011, following Air Force calls to discontinue its use as a satellite lifter. However, in September of that year, NASA added the Delta II to its NASA Launch Services (NLS)-II contract, which provided for four more bookings, of which ICESat-2 is the last.

 

 

 

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