The International Space Station is the largest structure ever built in space. The outpost, the product of 15 countries and five different space agencies, carries a an international crew of six people when fully staffed. But to support that crew, NASA and its partners rely on robotic cargo ships to ferry food, supplies and other vital gear to asttronauts. Here's a look at the robot delivery ships that make those important supply runs:
The European Space Agency's "Edoardo Amaldi" Automated Transfer Vehicle-3 (ATV-3) is one of a suite of robotic spacecraft that deliver goods to the International Space Station. Europe's ATV vehicles are huge, large enough to fit a London double-decker bus inside.
In this photo, the Automated Transfer Vehicle-3 (ATV-3) approaches the International Space Station on March 28, 2012.
Japan's HTV vehicle is another robotic cargo ship that ferries supplies to the space station. Here, it is shown just before astronauts grapple it on Jan. 27, 2011. Japan's HTV vehicles have the unique ability to carry cargo inside a pressurized section (for astronaut use) and in a exterior compartment for external use.
Backdropped by Earth's horizon and the blackness of space, the first unpiloted Japanese H-2 Transfer Vehicle (HTV) approaches the International Space Station on Sept. 17, 2009.
Russia's Progress ships are the workhorses of the cargo freighter fleet. More than 30 of these expendable vehicles have supplied the ISS.
This infographic profile of the Progress cargo ship used to service the International Space Station.
Here, the unmanned Russian Progress 42 cargo ship is seen by a video camera on the exterior of the International Space Station just before docking on April 29, 2011.
Dragon is an untested member of the cargo freighter fleet. This capsule is built by private company SpaceX (Space Exploration Technologies), and is due to fly its first delivery trip to the station in May 2012.
Dragon has already been flown on one test mission to orbit and back. Here, the flown capsule is displayed in Washington, D.C. on Feb. 10, 2011.
This graphic illustrates the design of SpaceX's Dragon, which is meant to carry people eventually.
Orbital Sciences Corp. is another private company developing an unmanned supply spaceship. This illustration shows Orbital's Cygnus spacecraft approaching the ISS.
Orbital Sciences' Cygnus spacecraft is scheduled to make its debut flight in 2012.
Cygnus, along with SpaceX's Dragon, has won a NASA contract to deliver goods to the space station in the coming years.