The Soyuz (Russian: Союз, meaning "union", GRAU index 11A511) was a Soviet expendable carrier rocket designed in the 1960s by OKB-1 and manufactured by State Aviation Plant No.

It featured the 8D74M RD-107 and the RD-110 engines from the 8K78M,[2] The new, uprated core stage and strap-ons became standard for all R-7 derived launch vehicles to replace the numerous older variants in use.

[3] The AVD malfunction detection system, variants of which are a standard component of all Soviet/Russian SLVs, would issue an automatic shutdown command to the booster if operating parameters such as electrical power, engine performance, or flight trajectory deviated from normal, and on manned launches also activate the Launch Escape System.

This would prevent a malfunctioning launch vehicle from flying around erratically and ensure it fell to the ground and impacted in a predictable location.

The aborted Soyuz 18-1 launch in 1975 was the final crewed flight of the 11A511, and as it occurred shortly before the ASTP mission, the United States requested that the Soviets provide details about this failure.