1997: An unmanned "Progress" spacecraft collides with the Mir space station while attempting to dock.

Although the collision was relatively minor, it was remarkable for being the only accident involving a Progress ship. Human error – a fumble in coordination between ground control in Moscow and the cosmonauts aboard Mir – was probably to blame.

Despite the accident, the Progress in all its variations has proven to be a durable and reliable supply ship since becoming operational in 1978, and has served every Russian space station since Salyut 6. Designed as an expendable vehicle, Progress ships carry out their supply missions and then are burned up upon reentering the atmosphere.

Progress is basically a Soyuz capsule that has been stripped bare of human life-support systems and reconfigured to carry supplies. Several upgrades have maintained the craft's effectiveness over the years.

When the U.S. space-shuttle fleet was grounded in the wake of the Columbia accident, Progress ships stepped into the breach, providing the sole support for cosmonauts and astronauts serving aboard the International Space Station until the shuttles were cleared to fly again.

For all its dependability, however, the days of this workhorse are numbered. The Russians, like the Americans, are developing new-generation supply ships in both manned and unmanned versions. A major milestone came in May of 2012, when the SpaceX Dragon successfully docked with the International Space Station, transferring cargo before detaching and returning safely to Earth.

(Source: Various)

This article first appeared on Wired.com June 25, 2007.