TO SPACE STATIONS
has transported cosmonauts to and from space stations since 1971.
During the first decade of Soyuz use, the cosmonauts' planned stay
in orbit might exceed the battery life of their Soyuz spacecraft.
Therefore, the early versions of the Soyuz had to be replaced with
a fresh vehicle, just as food, water, and air supplies had to be
the replacement Soyuz could be guided to the space station without
a crew, cosmonauts usually ferried the vehicles, because periodic
visitors and crew exchanges were welcome changes in the orbital
routine. That sociable tradition continues in today's Russian space