The TKS spacecraft (Russian: Транспортный корабль снабжения) was a Soviet spacecraft conceived in the late 1960s for resupply flights to the military Almaz space station.

The spacecraft was designed for both crewed and autonomous uncrewed cargo resupply flights, but was never used operationally in its intended role – only four test missions were flown (including three that docked to Salyut space stations) during the program. The Functional Cargo Block (FGB) of the TKS spacecraft later formed the basis of several space station modules, including the Zarya FGB module on the International Space Station.

The TKS spacecraft consisted of two spacecraft mated together, both of which could operate independently:

The VA spacecraft (known mistakenly in the West as the Merkur spacecraft), which would have housed the cosmonauts during launch and reentry of a TKS spacecraft, while traveling to and from an Almaz space station.
And the Functional Cargo Block (FGB) which, in order to resupply an Almaz space station, carried docking hardware, tanks, and a large pressurized cargo compartment. Furthermore, the FGB carried the on-orbit maneuvering engines for the TKS.
While the VA carried the reentry hardware, and only minimal life support and maneuvering systems, the FGB would have been used as the primary orbital maneuvering system and cargo storage for the TKS spacecraft.

The FGB could also be used alone as an uncrewed cargo module without a VA spacecraft, which enabled the FGB design to be re-purposed as FGB space station modules later on. The VA spacecraft, on the other hand, was also intended to be launched as "Almaz APOS", mated with an Almaz-OPS space station core as the primary orbital maneuvering system, instead of an FGB.