245 DAY IN THE LIFE: VITAL VISITING VEHICLES—KEEPING THE REMOTE OUTPOST CREWED AND OPERATING CHAPTER 14 above, missions might overlap. More flexibility would be possible if two places were available for the cargo craft to berth on the USOS. After a significant amount of work, a second berthing port was added to the nadir side of the Node 1 module in addition to the one already present on the nadir side of Node 2. In the spring of 2016, two vehicles—a Dragon and Cygnus—were berthed to the space station at the same time, as seen in Figure 11. Figure 11. A view from the external cameras on the ISS showing the capture and berthing at Node 2 on April 10, 2016, of the SpaceX Dragon while the Orbital ATK Cygnus, which arrived previously on March 26, is parked on the nadir side of the Node 1 module. More to Come As with the ISS itself, vehicles that visit the space outpost are evolving as well. NASA purchased the services of the private companies SpaceX and Orbital ATK that build the Dragon and Cygnus vehicles, respectively, under the Commercial Resupply Services (CRS) contract, which was awarded in 2008. In January 2016, NASA announced the second phase of the supply missions, known as CRS-2. In addition to SpaceX and Orbital ATK, NASA selected Sierra Nevada Corporation, which is building the Dream Chaser spacecraft (Figure 12), to provide cargo missions. Sierra Nevada Corporation is expected to fly the first Dream Chaser mission in 2020. Image Courtesy Sierra Nevada Corporation Figure 12. The Dream Chaser cargo vehicle, to be developed by Sierra Nevada Corporation, berthed to the nadir port of the Node 2 module. It is estimated to fly in 2020. Following the retirement of the Space Shuttle, the ISS became completely dependant upon the Russian Soyuz to transport astronauts to and from the space station. Beginning in 2010, NASA partnered with commercial aerospace companies to develop crew transportation subsystems, followed by later development phases—an approach that was modeled after the successful CRS program. In September 2014, NASA selected two companies—Boeing and SpaceX— to develop the CST-100 Starliner and Crew Dragon, respectively, for this task. The first flight tests are