Site 43, also known as SK-3 and SK-4, is a launch complex at the Plesetsk Cosmodrome in Russia. It consists of a two pads, Sites 43/3 and 43/4, and has been used by R-7 derived rockets since the early 1960s.

The site was originally built for use by R-7A Semyorka missiles. The first launch to use the complex was an R-7A test on 21 December 1965, from Site 43/3. The first launch from 43/4 followed on 25 July 1967.

After its retirement from service as a missile base, it was converted for use as a space launch complex. The first orbital launch was of a Voskhod rocket with Kosmos 313 on 3 December 1969.

Both pads were damaged by explosions in the 1980s. At 16:01 UTC on 18 March 1980, 48 people were killed when a Vostok-2M exploded during fueling operations at Pad 4. The disaster injured dozens more, while damaging the pad so severely that it was not used again until 1984. On 18 June 1987, a Soyuz-U rocket exploded at liftoff on Pad 3. Both were rebuilt, and are in service as of 2009.



The Vostok-2M (Russian: Восток meaning "East"), GRAU index 8A92M was an expendable carrier rocket used by the Soviet Union between 1964 and 1991. Ninety-three were launched, of which one failed. Another was destroyed before launch. It was originally built as a specialised version of the earlier Vostok-2, for injecting lighter payloads into higher sun-synchronous orbits. It was a member of the R-7 family of rockets, and the last Vostok.

The Vostok-2M made its maiden flight on 28 August 1964, from Site 31/6 at the Baikonur Cosmodrome, successfully placing Kosmos 44, a Meteor weather satellite into orbit. Its only launch failure occurred on 1 February 1969, when the launch of a Meteor failed due to an upper stage problem.

At 16:01 GMT on 18 March 1980, a Vostok-2M exploded during fueling at Plesetsk Site 43/4, ahead of the launch of a Tselina-D satellite, killing 48 people who were working on the rocket at the time. A filter in a hydrogen peroxide tank of the third stage had accidentally been soldered with lead instead of tin, with the catalytically active lead solder on the filter causing the explosion upon contact hydrogen peroxide. As a consequence, the H2O2 broke down, overheated, and melted the solder, causing pieces to fall into the H2O2 storage tank and cause a runaway chemical reaction. This led to a fire inside the third stage and eventual explosion which resulted in the complete destruction of the launch vehicle and severe pad damage (LC-43 did not host another launch for three years).

Vostok-2M launches occurred from Site 31/6 at Baikonur, and Sites 41/1 and 43 at Plesetsk. It is unclear if any were launched from Site 1/5 at Baikonur. The Vostok-2M was retired in 1991, in favour of standardisation on the Soyuz-U and U2 rockets. The final flight was conducted on 29 August, and carried the IRS-1B satellite for the Indian Space Research Organisation.