[image-36]The first Cygnus Spacecraft to visit the International Space Station (ISS), the G. David Low, departed the station at 7:31 AM EST on October 22, 2013. The Cygnus spacecraft is the latest in a long line of cargo vehicles built to resupply the orbital outposts that humanity has positioned in the heavens. Created by Orbital Sciences Corporation of Virginia, it is the second type of vehicle built by a commercial company to visit the ISS.

[image-96]As the Soviet long-duration space station missions grew in complexity in the late 1970s designers needed a way to supply the outpost with the resources needed for both man and machine. The crewed Soyuz craft of the time could only accommodate two suited Cosmonauts with room for little else. For enhanced operations on the Salyut 6 space station, the Soviets modified the Soyuz vehicle to serve as an automated cargo truck. Designated as “Progress” when first launched in 1978, the new vehicle was designed to replenish on-orbit supplies of oxygen, food, water, and fuel to reboost the station to maintain altitude. The Progress design has been modified a number of times, and is currently in use for the International Space Station.

Soviet spacecraft designers had pioneered the cargo vehicle concept in the 1960s with the design of their military space station series known as Almaz. The TKS spacecraft (Transportnyi Korabl’ Snabzheniia, or Transport Supply Spacecraft) had the ability to transport both crew and cargo simultaneously in one craft. Due to delays and cancellation of the Almaz program, the TKS was never used for its intended purpose. However, the TKS did make several successful uncrewed test flights, including three vehicles launched under the Cosmos designation to the Salyut 6 and 7 space stations. The cargo portion of TKS, known as the Functional Cargo Block, also became the basis for future Russian-built space station modules on both Mir and the International Space Station.

[image-51]The development of the multi-national International Space Station brought about the development of many new cargo vehicles to supply the needs of a large permanent crew. In addition to the planned use of the U.S. Space Shuttle and Russian Progress vehicles, two of the other international partners developed automated cargo vehicles as part of their contribution to the program. The European Space Agency (ESA) developed the Automated Transfer Vehicle (ATV). Carrying over 7,600 kilograms of cargo to the station, it is the largest resupply vehicle to visit a space station. The Japanese Aerospace Exploration Agency (JAXA) developed the H-II Transport Vehicle (HTV), which included an unpressurised section as well as a pressurized cargo section. The HTV can carry 6,000 kilograms of pressurized cargo. Progress, ATV, and HTV do not have the ability to return cargo to Earth. Instead, at the end of their missions they perform the important task of “taking out the trash.” All three vehicles are filled with unneeded materials, and after undocking, are de-orbited and burn up over uninhabited stretches of the Pacific Ocean.

With the retirement of the U.S. Space Shuttle, American resupply flights to the ISS took an 11-month hiatus. The commercial Dragon spacecraft, manufactured by Space Exploration Technologies Corporation (SpaceX) of California, became the first private/commercial vehicle to visit and resupply the ISS during its May 2012 test mission. Since then, SpaceX has completed two dedicated resupply missions with the Dragon vehicle. The Dragon spacecraft also offers another capability that the ISS has not had since the end of the shuttle program, the ability to return significant amounts of materials from space. In addition to the crew, the Soyuz craft can carry only a very limited amount of material back to the planet. However, the Dragon capsule can return significant quantities of material, including experimental samples that need to be kept frozen. Like the HTV, the Dragon also boasts the ability to bring unpressurized cargo to orbit.[image-80]

The latest new commercial space resupply vehicle, Cygnus, can carry 2,000 kilograms of cargo to the station. A slightly larger version capable of carrying an additional 700 kilograms is in development. Cygnus became the second dedicated service vehicle under NASA’s Commercial Orbital Transportation Services (COTS) project with it’s successful five-week demonstration mission in autumn of 2013. Although not intended specifically as a cargo vehicle, the U.S. Orion Multi-Purpose-Crew-Vehicle will also be able to bring supplies and crewmembers both to the space station and down to Earth when it begins to fly later in the decade. The cargo lifeline needed to supply our human foothold in space continues to become more robust with the addition of new capabilities from both international and commercial partners.

Learn more about the cargo vehicles visiting the International Space Station: http://www.nasa.gov/mission_pages/station/structure/assembly_elements.html