Going out in style: Delta II completes its final mission with launch of ICESat-2
LOMPOC, Calif. — A United Launch Alliance (ULA) Delta II rocket left the pad at Vandenberg Air Force Base’s Space Launch Complex 2 to send NASA’s Ice, Cloud and land Elevation Satellite-2 (ICESat-2) into polar orbit, beginning a new era in Earth observation and ending the career of the venerable Delta II.
Liftoff took place at 6:02 a.m. PDT (9:02 a.m. EDT / 13:02 GMT) Sept. 15, 2018. This was about 16 minutes into the 2 hour, 34 minute launch window. During a planned hold in the countdown at T-4 minutes, the hold was extended briefly to address a temperature issue on the second stage. At 5:56 a.m. PDT (8:56 a.m. EDT / 12:56 GMT) NASA Launch Manager Tim Dunn gave final approval to resume the countdown.
“With this mission we continue humankind’s exploration of the remote polar regions of our planet and advance our understanding of how ongoing changes of Earth’s ice cover at the poles and elsewhere will affect lives around the world, now and in the future,” said Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate, in a NASA news release.
In the lead up to the final Delta II flight, mission and launch teams successfully concluded the Launch Readiness Review Sept. 13. The 30th Space Wing at Vandenberg indicated that there would be a zero percent chance of a weather rule violation.
ICESat-2 carries a single instrument, the Advanced Topographic Laser Altimeter System (ATLAS), which records how lake it takes for laser pulses to return to the spacecraft. In so doing, it can produce a precise “map” of the Earth’s surface.
The spacecraft was designed and built by Northrop Grumman and is derived from the LEOStar-3 satellite bus used for NASA’s Landsat 8, the GeoEye-1 Earth imaging satellite and NASA’s Fermi Gamma-Ray Space Telescope. ICESat-2 has a design life of three years but carries enough fuel for up to seven years.
“While the launch today was incredibly exciting, for us scientists the most anticipated part of the mission starts when we switch on the laser and get our first data,” said Thorsten Markus, ICESat-2 project scientist at NASA’s Goddard Space Flight Center, in a NASA news release following liftoff. “We are really looking forward to making those data available to the science community as quickly as possible so we can begin to explore what ICESat-2 can tell us about our complex home planet.”
The detailed height measurements captured by ICESat-2 should enable researchers to precisely track changes on the surface, including glaciers, ice sheets, sea ice and forests. Because ATLAS is sensitive enough to detect individual photons, and with its rapid-firing rate, the instrument can detect both the forest floor and the tops of canopies in all but the densest forests and jungles.
Shortly after the Delta II 7420-10 rocket lifted off the pad, the vehicle made a pitchover maneuver to maintain a proper flight path while lessening dynamic forces on the launch vehicle.
The Delta II reached Mach 1 around 30 seconds into its flight and the moment of maximum dynamic pressure on the launch vehicle at the 46 second mark. The rocket’s four graphite epoxy motors were jettisoned 1 minute, 23 seconds into the flight.
Four minutes, 24 seconds into the flight, main engine cutoff occurred on the first stage. The rocket then entered a brief coast phase.
Separation of the first stage from the rocket’s second stage took place eight seconds later, followed by ignition of the second stage’s AJ10-188K engine 6 seconds after that.
The Delta II’s two-piece, 10-foot (3-meter) diameter payload fairing separated and was jettisoned 5 minutes into the flight. The first of four second stage engine cutoffs (SECO-1) occurred 10 minutes, 53 seconds after liftoff.
The second stage and satellite then entered a coast phase for about 36 minutes. At 47 minutes, 30 seconds into the flight the second stage engine reignited for a second burn, second stage engine cutoff two occurred 7 seconds later.
At 52 minutes, 40 seconds from liftoff, the second stage released the ICESat-2 satellite into orbit.
The spacecraft will now undergo a 60-day check-out period where the spacecraft and ATLAS instrument will be tested to make sure everything is functioning properly.
About 18 minutes after deployment, the second stage engine ignited for a third burn. The Third SECO occurred nearly 71 minutes into the mission.
About 1 hour, 16 minutes after liftoff, the second stage began deploying the mission’s secondary payload of four CubeSats: Cal Poly’s Damping And Vibrations Experiment (DAVE), UCLA’s two Electron Loss and Fields Investigation (ELFIN) CubeSats, and the University of Central Florida’s SurfSat.
These small satellites will conduct research on space weather, changing electric potential and resulting discharge events on spacecraft and damping behavior of tungsten powder in a zero-gravity environment.
The booster that lofted ICESat-2 was built four years ago and bore the number 381 on its side. For the early flights of the Delta II program, stars were placed on the rocket for every successful flight in a row. The stars were brought back for this flight. Delivering ICESat-2 to orbit was the 155th flight for the Delta II since its first launch on Feb. 14, 1989.
“The Delta II was a very reliable and very dedicated rocket for a long time,” Dane Drefke, mechanical operations lead engineer at ULA told SpaceFlight Insider. “People don’t realize how this little rocket has changed their lives.”
The Delta II rocket was created by McDonnell Douglas in the late 1980s to launch GPS satellites for the U.S. Air Force. Between 1989 and 2009, the Delta II successfully deployed four dozen navigational spacecraft to form and maintain the operational constellation.
It was on the GPS IIR-1 mission that the rocket encountered its most public failure. On Jan. 17, 1997, just 13 seconds after it had left the pad, the rocket’s number 2 solid rocket booster ruptured, resulting in an explosion and the total loss of the mission.
“Some of the newer rockets, like Vulcan, are a generation more advanced in technology,” said Drefke, who was worked on Delta II off and on for 22 years. He expressed sadness that its era had passed but believes the rocket’s mission was “absolutely well done.”
The Delta II has also been used for more than 50 NASA missions, including eight Mars missions between 1996 and 2007. The Delta II also launched other missions to explore our solar system including NASA’s MESSENGER mission to orbit Mercury and the Dawn spacecraft that explored Vesta and Ceres.
The launch vehicle was also selected to loft the Kepler observatory to discover exoplanets and the Spitzer Space Telescope that studies the universe in infrared.
“Godspeed, Delta II,” said a member of the launch team at the conclusion of the CubeSat deployments, “and thank you for your almost 30 years of unparalleled excellence.”
Following the successful flight, United Launch Alliance issued a statement that the last (unflown) Delta II rocket would be displayed at the Kennedy Space Center Visitor Complex, joining a number other retired launch vehicles at the tourist destination and serving to remind viewers of its many accomplishments.
“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 Tory Bruno, ULA president and CEO. “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.”
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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.