With the successful launch on Friday of a SpaceX Dragon cargo ship bound for the space station, (not to mention a dramatic landing of the reusable first stage at sea) the orbiting outpost is about to receive its fourth visiting vehicle in as many weeks.
When the Dragon arrives on Sunday, it will take the station’s last free parking space—a port on the underside of the Harmony module, facing Earth (red arrow in the diagram below). The last time six vehicles were docked to the station was back in the shuttle era, when Discovery visited on the STS-133 mission in February 2011. At that time there were two Soyuz taxis attached (always the case when six people are onboard, since they would serve as lifeboats in an emergency), as well as Russian, European, and Japanese cargo ships.
Sunday will mark the first time two U.S. commercial cargo vehicles are docked at the same time—a Cygnus ship has been attached to the station since March 26. Two Soyuzes and two Russian Progress cargo ships are also docked at the moment. Among other supplies, the Dragon is bringing up a new inflatable “room” for the station called BEAM, which will be attached to a berthing location (which is different from a docking port for vehicles) on the Tranquility module. Space station logistics managers say the flurry of visiting ships finally catches them up after a string of spacecraft accidents starting in October 2014 disrupted the station’s supply chain.
The Russian side of the station has four docking ports, while the U.S. side has two. The next Dragon supply mission, scheduled for this summer, will carry up the first of two new International Docking Adapters, which eventually will bring the total number of ports to eight—although NASA doesn’t plan for more than seven vehicles to be parked at the station at any one time.
Got it? Either way, it’s probably best to call ahead if you plan to visit the station, just to make sure there’s a free space.