– Xochielt Sanchez
Answer by Clayton C. Anderson:
Astronauts and cosmonauts on the International Space Station (ISS) have multiple ways to receive "cargo" from Earth these days. The frequency may vary slightly over time, but roughly speaking, they tend to receive/welcome new cargo ships on a near "quarterly" basis.
First and foremost is the "old workhorse" known as the Russian Progress. These solid ships have been delivering cargo to space safely and successfully for many years. Attractive because of their reliable performance, and ability to dock to ISS automatically, they are also –once their delivered cargo is offloaded– loaded with unwanted trash and equipment that is no longer needed on board. Once "stuffed to the gills", the ship will eventually undock and burn up in the earth's atmosphere. Sort of a spaceflight incinerator.
Since the space shuttles were retired (they were truly the "big dogs" of cargo delivery with their 60-foot long and 15-foot diameter payload bays), other "players" have entered the game, in an analogy much like the trendy phrase used in modern day football, "… next man up!" Popular among the media (and NASA) is SpaceX, Elon Musk's commercial spaceflight company. Using their Dragon capsule, NASA has "hired" them to deliver… and return... cargo to/from the ISS. Their ability to deliver science experiments, data and biological collectibles (urine, blood samples, etc.) back to earth is key. So far, they are doing outstanding work.
Orbital Sciences Corporation is another commercial company "hired" by NASA for delivering cargo (but they don't return anything to earth) to ISS. After a couple of successful missions, they experienced a critical failure during their last launch attempt, resulting in the loss of their rocket and its cargo carrying Cygnus capsule. They are still in the process of recovering from this incident. I am betting they will successfully return to the ISS cargo delivery business. When…? That part I don't know.
Finally, in the international consortium known as the ISS Program, the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA) both have demonstrated cargo delivery capability as well. ESA's Automated Transfer Vehicle (ATV), which I liken to a "Progress on steroids", is nearing the end of its agreement with the ISS Program for deliveries. Built with the help of the Russian Space Agency, it is larger and "brighter" (more modern) than a Progress, but no less dependable. They were signed up for 4 deliveries as I recall. JAXA and their H-II Transfer Vehicle or HTV had similar agreements for a limited number of cargo delivery flights. Unique to the HTV, is its ability to use the ISS Japanese Experiment Module (JEM) –also a JAXA contribution to the ISS– robotic arm to help "empty" portions of its cargo load and place it on the external porch of the JEM. Both ATV and HTV have successfully completed multiple cargo deliveries to the ISS.
It remains to be seen how the ISS Program will one day try (maybe they won't?) to get larger pieces of equipment (e.g., new external solar array batteries or thermal system pump modules, etc.) to ISS. Prior to the shuttle program's demise, many spare parts were delivered to space and are now stored externally on platforms called ISP's or Integrated Stowage Platforms. "Living outdoors" in the harsh environment of outer space could pose potential problems when the equipment is one-day needed to operate. We shall see!
Keep lookin' up… and, as the crews on the ISS are sure to say, "keep deliverin'!"