NASA says the pace of research aboard the International Space Station (ISS) is accelerating - even though the shuttles used to build it were recently retired.
Indeed, the US and its partners have supported a continuous presence on the station for the past 11 years, and the laboratory is expected to operate at least through 2020.
As such, the United States and its international partners routinely deploy a variety of vehicles to transport research materials and equipment to and from the station.
Part of this international effort also involves commercial providers in various stages of their vehicle's completion, which are being contracted by NASA to deliver cargo to the station and return research samples to the Earth.
Currently, all astronauts traveling to and from the ISS hitch a ride aboard the Russian Federal Space Agency, or Roscosmos, Soyuz vehicle. Roscosmos also provides the Progress unmanned cargo resupply ships that deliver supplies to the orbiting outpost. Both vehicles use automated systems to dock to the station. The Soyuz returns the crew and a limited amount of cargo home, while the Progress - filled with trash - burns up upon re-entry to the Earth's atmosphere.
The Automated Transfer Vehicle, also known as ATV and designed by the European Space Agency, is an unmanned cargo carrier capable of automatically docking with the station. The Automated Transfer Vehicle is capable of carrying in excess of 16,800 pounds (7,620 kilograms) of cargo, including dry goods, water, gases and propellant. Once the cargo is unloaded, the vehicle is used as a garbage container, with the carrier and enclosed waste burning up upon re-entry to the Earth's atmosphere. Two Automated Transfer Vehicles have visited the station to date.
Meanwhile, the Japan Aerospace Exploration Agency provides the H-II Transfer Vehicle, also known as HTV, which is the only vehicle, besides the shuttle, capable of transporting external cargo to the station. This vehicle is captured with the station's robotic arm and berthed to the designated port, with two visiting the station so far. Like the Automated Transfer Vehicle, the H-II Transfer Vehicle's cargo is unloaded, and the vehicle is used to collect trash. The vehicle also burns up upon re-entry.
Two commercial resupply service providers are projected to complete flight demonstration capabilities and make deliveries to the station in 2012. Both spacecraft will use the station's common berthing mechanism ports that provide shirtsleeve conditions and large passageways for cargo transfers into the station. The two vehicles also require berthing to the station, after capture with the station's robotic arm.
SpaceX's Dragon spacecraft is currently contracted to complete 12 missions. Late April 2012 is targeted as the new launch date for the second demonstration flight to the space station, with the vehicle to be berthed upon arrival. Test cargo will be transferred and returned on the demo flight.
Similarly, Orbital's Cygnus vehicle is contracted to provide eight missions between 2012-2015, and will be berthed to the station. Approximately 44,092 pounds (20,000 kilograms) of cargo is planned for delivery to the station, along with disposal of station trash upon the vehicle's re-entry. Cygnus' pressurized cargo module is based on the station's Multi-Purpose Logistics Module, also known as the MPLM.