Samos 3 exploded on LC 1-1 at PALC on September 9, 1961. A pad umbilical did not detach at liftoff, which caused the Atlas-Agena B to switch from internal to external power. The engines shut down and the Atlas dropped back onto the pad and exploded in a huge fireball, resulting in the total loss of the photoreconnaissance satellite.Pad damage was evidently not that bad as Samos 4 flew from LC 1-1 only nine weeks later.
So how is the Sea Launch NSS-8 launch failure in jan. 30, 2007 counted. Would this be considered an American launch failure due to partial Boeing ownership? Also wouldn't, okay just checked F9 contains ~20% more propellants than the Zenit. So would it be the second largest US pad explosion? Third going to AC-5?
The fifth Thor test on October 3, 1957, was launched from LC-17A. In a near repeat of Thor 101, the missile lost thrust almost immediately at liftoff, fell back through the launch stand, and exploded. This incident was traced to a failure of the gas generator valve to open.Pad damage was evidently quite minor, as LC-17A hosted the launch of Thor 108 on October 24, only 21 days later.
Stretching to test stand explosions, what about the Titan IV booster (after a redesgin became the srmu) explosion at Edwards AFB? Only 280 tonnes of prop though...
Thanks for adding this one! This was Atlas 106 D and Agena B A2201. I have to date found no photos of the failure or its aftermath. This could have been a more powerful explosion than Atlas-Able, the previous U.S. largest. At the time, Atlas Agena B was the largest, most-powerful U.S. launch vehicle. The next launch from Point Arguello LC 1-1 (later renamed VAFB SLC 3 West) took place on November 22, 1961. It also failed, but not on the pad.
The Thor was built with separate propellant tanks. If it fell back onto the pad in a more or less vertical orientation, the vehicle descended below the pad deck through the center hole, hit the flame deflector and skidded along it, breaking neatly into two parts, one fuel and one oxidizer. One tank would break open below the deck, the other above. The propellants didn't inertially mix as thoroughly as was the case on other pads, such as Atlas. While there was a still large conflagration, the blast effects were less than were seen on other stands.
N-1 5L: The LOX turbopump for engine no. 8 exploded just before liftoff. The rocket managed to clear the tower, at 10 seconds into the flight the KORD system started shutting down 29 of the 30 engines. The rocket crashed on the pad, wiping it out and damaging the second N-1 pad nearby. The photo shows the escape system firing to yank the capsule away from the N-1 as it begins to fall back down onto the pad.