SpaceX SLC-6 takeover to mark a new chapter for a famous pad

by Chris Bergin

One of the most iconic launch sites in the world, Vandenberg Space Force Base’s Space Launch Complex 6 (SLC-6), will be leased by SpaceX. Confirmation came after Col. Rob Long, Space Launch Delta 30 (SLD 30) commander, signed a statement supporting SpaceX’s lease to launch Falcon 9 and Falcon Heavy missions from the launch site.

SLC-6 was under the stewardship of United Launch Alliance (ULA) for the launch of its west coast Delta rockets before vacating the site after its final Delta IV Heavy launch in Sept. 2022. The launch site was also famously set to become the west coast launch site for the Space Shuttle before plans were canceled in the mid-80s.
Prior to ULA’s acquisition of the launch site, though, SLC-6’s history was one of cancellations.

Work originally began on the complex on March 12, 1966, to support launches of a modified Titan III rocket in preparation for the Manned Orbiting Laboratory (MOL). With its polar orbit obligations, Vandenberg’s SLC-6 underwent extensive work to prepare the site for launching the series of 30-day missions.

SLC-6 during its MOL period. (Credit: NSF/L2)

However, the program was canceled three years later, placing SLC-6 into a mothballed status.

Even before the Space Shuttle had even launched, Vandenberg was selected as a second launch site for America’s newest space program. For civilian and military payloads requiring equatorial orbits, Space Shuttle flights would be launched out of the Kennedy Space Center’s (KSC) two pads, LC-39A and LC-39B, while military payloads requiring polar orbits would be launched from SLC-6.

The decision to select Vandenberg was due to multiple factors, ranging from the large payload penalties involved with polar orbit inclinations out of KSC, and the dangers associated with flying over U.S. states, specifically South Carolina, during ascent. There was also the risk that the discarded External Tank’s deorbit corridor would have it reenter over Canada and Russia – as opposed to the usual deorbit corridor over the Indian Ocean.

This decision was made as early as 1972, with SLC-6 confirmed as the West Coast home for Shuttle in 1975 – a full six years before STS-1 launched from 39A.

Modifications of SLC-6 to ready the pad for Shuttle. (Credit: NSF/L2)

With NASA’s fleet of Shuttles all housed at KSC, the conversion of SLC-6 took place between 1979 and 1986. This was a considerable undertaking, costing around $4 billion, even with a compacted version of the KSC setup. All of the pad’s significant buildings were kept in the same locations, although plans to have the launch control center placed just 500 yards from the pad were soon changed to place it far away from the Blast Danger Area.

**L2 SLC-6 Construction Photos and Stories from Shuttle Engineers**

An inline processing path would see the large payload preparation building be located next to the payload changeout and Shuttle assembly buildings. With a service structure and launch mount fixed in place, the mobile service tower was placed at the far end of the pad. The assembly and service structures were on rails and would roll back ahead of a launch.

SLC-6 in the proper configuration to support Shuttle. (Credit: NSF/L2)

Space Shuttle Enterprise continued her post-flight test role as a fit check vehicle, which she had enjoyed at KSC. When the teams at SLC-6 were ready for fit checks, Enterprise was flown over to California and rolled down narrow roads – having already been expanded to cater to her wingspan – to the Vandenberg site.

Once at SLC-6, Enterprise conducted flows that mirrored those of a returned orbiter preparing for her next flight. This included being mated with an external tank (ET) and solid rocket boosters (SRBs) on SLC-6. According to workers at Vandenberg, numerous challenges had to be worked through during these tests, mainly relating to having to adapt to an entirely new setup.

Enterprise on the pad during fit checks at SLC-6. (Credit: NSF/L2)

However, the tests were eventually completed and preparations began for welcoming Space Shuttle Discovery to the west coast. Vandenberg would become her new home for future United States Air Force (USAF) missions to polar orbits.

**L2 Restored Photos from SLC-6 Shuttle**

Discovery would have undergone a flight readiness firing at the pad ahead of a mission that had several mission designations, including STS-1V and STS-62A. STS-1 pilot Bob Crippen was to be commander, with the launch planned for Oct. 15, 1986.

The STS-62A crew that was to fly the maiden Shuttle flight out of Vandenberg. (Credit: NASA)

However, everything came to a halt in early 1986 following the loss of Space Shuttle Challenger during STS-51L and the resulting grounding of the Shuttle fleet. Some experts argue this wasn’t the sole reason Shuttle operations came to a halt at SLC-6, though. Nonetheless, given the fallout from the tragedy, which would see the USAF pull out of using the Shuttle for military payloads, the primary rationale behind the use of Vandenberg for Shuttle launches was lost.

Interestingly, it was later revealed that had Shuttle continued towards its West Coast debut, other issues related to the pad itself would have impacted Shuttle operations and the overall use of SLC-6 for the program. These issues ranged from a lack of wastewater treatment to the need for additional water supply for the pad’s sound suppression system.

The latter issue raised major concerns surrounding how the acoustical energy shockwaves produced by the SRBs would have rebounded off the hilly landscape around SLC-6. However, former Shuttle workers are torn on this issue, some claiming it would never have been a concern. Tests were conducted using a helicopter hovering high over the pad at various altitudes before setting off explosives from time to time to measure the reflected acoustical energy.

SLC-6 from the air. (Credit: NSF/L2)

There were also concerns over more problematic icing on the vehicle than in Florida, with ice being a debris concern for ascent, through to an explosion risk associated with entrapped gaseous hydrogen due to the compact nature of the launch site.

However, these problems were also solved ahead of time. Amazingly, to deal with the fog and humidity conditions that could cause ice to form on the ET, teams installed two jet engines down off the pad with ductwork running up and exhausting between the tank and the orbiter to melt the ice. In addition, a steam injection solution was employed for the gas entrapment issues.

Enterprise on SLC-6 – via NSF/L2

There were many other stories, some rather amusing, such as soap and water being required to keep ducts clear of debris and toilet paper beefing up the HEPA filters at the pad.

With the use of Vandenberg as a Shuttle launch facility no longer planned, a $4 billion effort was required to decommission SLC-6, leading to its official stand-down in 1989.

Hopes that SLC-6 would finally conduct a launch were raised just months later when Lockheed Space Operations Company was awarded a USAF ground system contract to modify the site into a Titan IV/Centaur launch complex. Ironically this would have returned SLC-6 to its Titan III days when teams were preparing for the MOL. However, like MOL, the plans were canceled due to insufficient Titan IV launch requirements from the west coast.

In the mid-1990s, SLC-6 would finally see some launch action, when a small “milkstool” platform was installed on the former Shuttle launch mount for the Lockheed-Martin Launch Vehicle I (LMLV-1). The launch of LMLV-1 was the first rocket to launch on this smaller setup, albeit with a failure during ascent.

LMLV-1 was later renamed Athena I, with a successful launch of NASA’s Lewis satellite into orbit from SLC-6 taking place on Aug. 22, 1997. An Athena 2 rocket also enjoyed a successful launch campaign from SLC-6 two years later with the launch of the Ikonos satellite.

Plans to return large launch vehicles to SLC-6 would be proposed at the end of that decade, with Boeing selecting and modifying SLC-6 for its Delta family of rockets for the Department of Defense’s Evolved Expendable Launch Vehicle (EELV) program. With a later transition into the United Launch Alliance (ULA), numerous Delta IV and Delta IV Heavy rocket launches would take place from SLC-6.

ULA’s final launch from SLC-6 came at the end of Sept. 2022 with its Delta IV Heavy rocket. ULA is phasing out its Delta and Atlas V rockets to be replaced by their upcoming Vulcan-Centaur launch vehicle. For a west coast launch pad for Vulcan, ULA will utilize their former Atlas pad, SLC-3.

It was rumored that Blue Origin might be interested in SLC-6’s future before the surprise announcement that SpaceX had leased the complex. SLD 30 noted the decision was the result of its launch pad allocation strategy, a process to evaluate the suitability of various launch sites for different types of rockets and payloads.

SpaceX already launches Falcon 9 from Vandenberg, utilizing SLC-4E. Per the initial plans, this was also set to be a Falcon Heavy capable pad. SLC-6’s allocation to SpaceX explained that both Falcon 9 and Falcon Heavy will launch from the newly acquired pad.

A render of Falcon Heavy on SLC-6. (Credit: Jay DeShelter for NSF)

Somewhat interesting is that was the plan for the initial use of SpaceX’s launch facility in Boca Chica, Texas – before the plans evolved into Starbase and the launch and production center for their Starship rocket. It has been claimed that if SpaceX opted for a West Coast Starship launch site, SLC-6 would be the favored option.

SLD 30 added that this decision was part of the first round of launch pad allocations, and additional rounds of allocations will occur after further operational analysis.

“This is an exciting time for Vandenberg Space Force Base, our nation’s premier West Coast launch site for military, civil, and commercial space operations,” said Col. Rob Long, SLD 30 commander. “This agreement will add to the rich history of SLC-6 and builds on the already strong partnership with SpaceX.”

(Lead image: Space Shuttle Discovery flies over Vandenberg’s SLC-6. Credit: NASA)

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