ICESat2 was launched by the final Delta II rocket out of Vandenberg AFB this morning:
This is the end of the Thor era.
The Thor rocket first flew in 1957, as an intermediate range ballistic missile. It made its first orbital launch in 1959, placing Discoverer 2 into orbit. (Discoverer 1 was lost during an earlier Thor launch attempt.) Despite its origin as a missile, it soon became a workhorse launch vehicle called Delta. For the military, it launched reconnaissance payloads (including the first Corona satellites), the Transit satellite navigation constellation (the first satnav, predecessor to GPS), and as Thor, continued to perform missile tests including the “Operation Fishbowl” series of high altitude nuclear detonations. For civilian operators including NASA and NOAA, it launched the TIROS weather satellites, Pioneers 5-9, and early commsats such as Echo 1A. In the mid-60s it launched the Syncom satellites, the first geosynchronous commsats. It placed Landsats into orbit, and the first GOES satellites, bringing the world its first 24-7 full-disk imagery from geostationary orbit. In the 80s, it launched the Solar Max satellite that would later be captured and repaired by a Space Shuttle crew. In the same decade, the design was licensed to Mitsubishi Heavy Industries in Japan, which built it into the N-1 and then H-1 rockets, launching out of Tanegashima Space Center. (Today, they have retired these rockets in favor of all-domestic designs.) But the launch rate went down dramatically, as both the USAF and NASA had invested considerably in the Space Shuttle as a new means of putting payloads into space. Delta would be retired, surviving only in foreign launches. Delta stopped production, as did Titan 34 and Atlas-Centaur.
But the Space Shuttle wasn’t turning around its launches as fast as intended, and the loss of Challenger and her crew in 1986 was a crushing blow to this concept. The US government now wanted to minimize the use of human crews for payloads that didn’t really benefit from them. In response, McDonnell-Douglas revived the Thor for a new rocket type: Delta II. It became a very reliable workhorse, placing most of the GPS constellation in orbit as well as many NASA earth-observation spacecraft. (GEOTAIL, one of its earlier payloads, is still in operation today.) It lauched the majority of NASA’s missions to the red planet: Mars Global Surveyor, Mars Pathfinder, Mars Climate Orbiter, Mars Polar Lander, Mars Odyssey, both Mars Exploration Rovers (Spirit and Opportunity), and Mars Phoenix Lander. It launched many of NASA’s space telescopes (Spitzer, Swift, GLAST, Kepler, Wise), the sample return missions Stardust and Genesis, asteroid explorers (NEAR-Shoemaker, Deep Impact, and the massively successful Dawn that’s still orbiting Ceres today), the MESSENGER probe to Mercury, and a whole host of Earth orbiting spacecraft for NASA, NOAA, and the military. Delta II has worked hard and reliably, and it will be missed even as other rockets take up its burdens. Delta III was also Thor-legacy, but it retired when Delta IV came along. (Delta IV is a Delta in name only, not wearing the classic blue livery due to its liquid hydrogen fuel, while the old Thor-heritage rockets all ran on kerosene. And it, too, is likely to retire soon.) The Japanese Thor-based designs have also retired.
In addition to closing out a long and venerable chapter in the history of rocketry, today’s launch gave the Delta II a rare and enviable record: 100 successful flights in a row. Out of 156 launch attempts, 154 were complete successes, and only one was a complete failure. Granted, that was a pretty spectacular failure…..
No more Delta IIs are expected to be purchased, but Boeing plans to assemble the remaining spare parts to create a near-complete rocket for static display at the KSC visitor center, hopefully with the shark’s tooth livery that it wore for GPS flights: