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Cargo ships that supply the space station

Charles Black, Founder and CEO of Sen
May 21, 2015, 16:47 UTC

Sen—With Europe having completed its final cargo mission to the International Space Station in late 2014, what cargo freighters currently serve the International Space Station?

Following the final mission of the European Space Agency's ATV (Automated Transfer Vehicle), there are now just two nations, Russia and Japan, which are capable of delivering supplies to the orbiting laboratory. In addition, two U.S. commercial space companies have contracts to resupply the station.

Only one vehicle, SpaceX's Dragon, is able to return goods to Earth—the other cargo freighters all burn up on reentry, as designed.

Cargo deliveries have faced a challenge in recent months, with failures of both Orbital ATK's Cygnus and Russia's Progress M-27M to reach the orbiting complex.

The European Space Agency's ATV completed all five of its supply missions successfully. The agreement to provide five missions was part of a broader barter agreement between Europe and its space station partners—instead of cash to contribute to the running costs of the ISS, Europe agreed to build a cargo ship and deliver supplies. Despite its success there are no plans at present for any further missions for the unmanned freighter, though its technology will be adopted to help power the Service Module for NASA's Orion crew vehicle.

In September 2015 NASA will award new cargo resupply agreements to cover supplies for the period 2018-2024, the anticipated end of life of the International Space Station. As well as SpaceX and OrbitalATK bidding for follow-on contracts, bids are also expected from Lockheed Martin, Boeing and Sierra Nevada Corporation, the latter two planning to revamp their passenger spaceships to accommodate cargo. Lockheed Martin's cargo ship proposal comprises of a reusable tug called Jupiter and a cargo carrier called Exoliner.

Russia's Progress

Russia's Progress freighter is the long-standing workhorse of the supply fleet, having first delivered supplies to the ISS in 2000—two years before Elon Musk had even set up SpaceX.

The spacecraft can carry 1.7 tons of supplies as well as fuel for boosting the station's orbit. Once attached, it uses fuel it carries specifically for the purpose of boosting the station's orbit which is required from time to time to maintain the space station's altitude or to take avoidance action against space debris. Europe's ATV also used to carry fuel for this purpose.

Progress measures 7.4 metres by 2.7 metres, and is launched into orbit aboard one of the Soyuz rockets which currently lift off from the Baikonur Cosmodrome in Kazakhstan. Though its traditional journey to the ISS was a 34-orbit, two day timeframe, since 2012 this has been shortened in most cases to a four-orbit, six-hour flight profile. Once it arrives at the orbiting laboratory it uses an automated, radar-based system called Kurs—monitored by mission controllers—to approach and dock with the Russian Pirs module.

Whilst docked with the orbiting complex, it is used to store trash. When it undocks, full of rubbish, and returns to Earth, the bulk of the spacecraft burns up in the atmosphere during a controlled reentry.

The Progress carrier has not been without its failures, most recently the Progress M-27M spacecraft that was launched on April 28 failed to reach orbit and eventually fell back to Earth.

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The Russian Progress 42 spacecraft in orbit. Image credit: NASA

Japan's Kounotori (HTV)

Japan also supply the space station with their vehicle known as Kounotori (white stork), also referred to as HTV (H-II Transfer Vehicle). The vehicle, shaped like a can of fizzy drink, is the size of a bus, measuring over four metres wide by nearly ten metres high. It is launched by the H-IIB launch vehicle from Japan's Tanegashima Space Center and can carry up to six tons of supplies, of which 4.5 tons can be pressurized cargo.

Once Kounotori arrives at the ISS, it is captured by the station's robotic arm, Canadarm2, and moved to its docking position with the the Harmony module, as happens withSpaceX's Cargo Dragon.

Since its first succcessful demonstration mission, which launched HTV-1 on Sep. 11, 2009, Kounotori has made three further supply missions: Kounotori 2 in January 2011 (returning to Earth on March 30, 2011); Kounotori 3 (launched in July 2012 and returned in September 2012) and Kounotori 4 (launched on Aug. 4, 2013 and returned in September 2013). Kounotori 5 launched to the space station in August 2015. 

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Japan's HTV-4 in orbit. Image credit: NASA/JAXA

SpaceX Dragon

SpaceX, the U.S. commercial space operator founded by entrepreneur Elon Musk, became the first ever company to send a commercial spaceship to the ISS in May 2012 during a demonstration mission to prove to NASA that the spacecraft was capable of transporting cargo to the orbiting outpost and able to berth successfully with it.

SpaceX has a $1.6 billion Commercial Resupply Services (CRS) contract with NASA, agreed back in December 2008 to carry 20 metric tons of cargo to the ISS, expected to require up to 12 missions to the space station. A contract modification was executed on Sep. 30, 2014 to add three additional missions to cover supply through to the end of 2017. The company completed its first supply (CRS-1) in October 2012. So far the company has successfully completed six resupply missions.

The Cargo Dragon is the only vehicle of the current providers that is capable of returning equipment and goods to Earth. On reentering Earth's atmosphere the capsule splashes down in the ocean from where it and its contents are recovered.

SpaceX is also developing a crewed version of Dragon to ferry astronauts to and from the space station.

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SpaceX's Dragon in orbit during its fourth commercial resupply mission CRS-4. Image credit: SpaceX

Orbital ATK Cygnus

Orbital ATK is the second of the U.S. companies with a NASA contract to supply the space station. Orbital ATK was awarded a $1.9 billion contract by NASA in 2008 to deliver 20 metric tons of cargo. The contract was for a maximum of eight supply missions, but a contract modification executed on Dec. 15, 2014 added one extra mission to cover the station supply to the end of 2017. 

Its Cygnus cargo freighter is launched by an Antares rocket. In April 2013 Orbital ATK became the second company to send a spacecraft to the ISS, successfully demonstrating its capabilities to NASA. A second demonstration mission, as required under NASA's Commercial Orbital Transportation Services (COTS) program, took place successfully in September 2014.

Its first resupply mission under its CRS contract saw the Cygnus supply ship berth with the ISS in early 2014. Orbital ATK's second resupply mission took place in July 2014. Disaster struck however during its third mission in October 2014 when the Antares launcher exploded about 11 seconds after liftoff from Wallops Island, Virginia, destroying the Cygnus cargo truck it was carrying.

An upgraded Antares launcher is slated to fly again in 2016; until then OrbitalATK will use an Atlas 5 United Launch Alliance rocket to put the next Cygnus into orbit.

The Cygnus spacecraft can deliver 2.7 tons of pressurized cargo to the space station. On its return it burns up in the Earth's atmosphere during a controlled reentry.

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OrbitalATK's Cygnus cargo ship grappled by the space station's robotic arm. Image credit: NASA