Space Launch Complex 2 (SLC-2) is an active rocket launch site at Vandenberg Space Force Base, in California, USA. It consists of two launch pads: Space Launch Complex 2 East (SLC-2E, originally LC 75-1-1), used by the PGM-17 Thor missile and several of its derivatives from 1958 to 1972; and Space Launch Complex 2 West (SLC-2W, originally LC 75-1-2), which has been in use since 1959 to launch the Thor-Delta family and Delta II, and is currently used by the Firefly Alpha.

Space Launch Complex 2 was originally part of Launch Complex 75 (LC 75) and was known by designation LC 75-1 or just 75-1 (and the launch pads were designated LC 75-1-1 and LC 75–1–2). The first launch out of the newly designated Space Launch Complex 2 was that of a Delta E with ESSA-3 on 2 October 1966 from SLC-2E.

SLC-2E and SLC-2W are located approximately 2,000 feet (610 m) apart.

SLC-2W was originally built to launch the PGM-17 Thor for use in suborbital tests, being jointly operated by the United States Air Force and the Royal Air Force in accordance to the IRBM's stationing in Britain as part of Project Emily. It saw its first launch on 17 September 1959, with launches being held over the next four months and all but one being successful. Following the last flight on 21 January 1960, the pad underwent the conversion into an orbital launch complex, as the Thor got decommissioned from missile use and was replaced by ICBMs such as the LGM-25C Titan II.

As per its new use, SLC-2W was subsequently designed to launch the Thor-Agena and the Thor-Ablestar to compliment the nearby SLC-1E and 1W in its capabilities of putting satellites into polar orbit. Over the next seven years, it was put into use 21 times for nineteen Agena and two Ablestar launches, with the overwhelming majority of payloads being reconnaissance satellites such as the KH-4 for military customers like the National Reconnaissance Office. With the Department of Defense seeing its payloads grow in size throughout the late 1960s (as seen by satellites such as the KH-9 and KH-11 getting developed), both the Thor-Agena and Thor-Ablestar were retired and SLC-2W received another modification, this time to act as the west coast site of the Thor-Delta and its derivatives to complement LC-17 at Cape Canaveral. Throughout this period of the pad's history, 26 Delta launches were performed at the site, carrying various payloads for the DoD, NASA, NOAA, and a handful of international agencies such as ESA. During the late 70s, a mobile service tower was constructed at SLC-2W to help support the various Delta evolution by creating an enclosed environment. As the 1980s arrived and went along, the site gradually saw slowing use in the wake of the Delta family's expected replacement with the Space Shuttle, which was slated to have its own west coast launch site at SLC-6. Despite all California Shuttle plans getting axed following the Challeneger disaster in 1986, SLC-2W only saw one last liftoff in this configuration on 18 November 1989, with a Delta 5000 being used to launch the Cosmic Background Explorer (COBE) for NASA.

After getting mothballed for a half decade, McDonnell Douglas revived SLC-2W in 1994 for use as the polar orbit site of their successor to the Thor-Delta, the Delta II. The first launch in this new era was on 4 November 1995, carrying Radarsat-1 for the CSA and a Deep Space Network test satellite for NASA. Over the next 23 years, the pad saw 45 Delta II launches and delivered various payloads to polar orbit for numerous governmental agencies and commercial customers. Among the more notable payloads of this era are Aqua, Aura, Gravity Probe B, and the Wide-field Infrared Survey Explorer (WISE). Additionally, SLC-2W followed the Delta II in changing hands regarding operation; it went from McDonnell Douglas to Boeing following their merger in 1997, and was subsequentally passed to United Launch Alliance following the 2006 formation of the Boeing-Lockheed Martin joint venture. The site eventually wound down in use again throughout the 2010s following the Delta II's retirement from Cape Canaveral in 2011, and saw its last flight of a Thor-derived vehicle (and last launch of one in general) with the launch of ICESat-2 on 12 September 2018.

Following the Delta II's retirement, SLC-2W was leased out to Firefly Aerospace and repurposed to launch the Firefly Alpha. During the demolition process, a fire broke out on October 15, 2020, inside the Delta II mobile service tower. The maiden flight of Firefly Alpha took place on September 3, 2021, and resulted in a flight failure. The second flight on 1 October 2022 was successful in reaching orbit.

SLC-2E, much like 2W, originally saw use by the USAF and RAF for missile tests of the Thor and saw four launches in 1958 and 1959. Following the retirement of the Thor, it got modified in 1960 to launch the Thor-Agena and Thor-Ablestar to increase launch cadence for the military at the base, and each rocket saw 23 and 6 launches from there respectively. Among the most notable launches of that era includes Alouette 1, the first Canadian satellite.

As the Thor-Agena and Thor-Ablestar got phased out from use in the late 1960s, SLC-2E likewise saw a gradual conversion for use by the Thor-Delta and Thorad-Agena. During this era, the pad witnessed a total of 19 launches of various government satellites, with fourteen being from the Delta line and five being from the Thorad family. The last launch from SLC-2E came on 12 March 1972, seeing a Delta N propel TD-1A into orbit for ESRO. Much like SLC-1E and 1W, SLC-2E got mothballed to concentrate launches in the area at SLC-2W.

In the years following its deactivation, most structures at SLC-2E have been demolished.

• Space Launch Complex 3E
• Space Launch Complex 4E
• Space Launch Complex 6

• Encyclopedia Astronautica - Vandenberg SLC-2

34°45′16″N 120°37′11″W / 34.7545°N 120.6198°W / 34.7545; -120.6198