A newly built tower stands at Launch Complex 41, where Boeing and United Launch Alliance will launch the CST-100 Starliner spacecraft. (Phelan M. Ebenhack for The Washington Post) The two contractors that NASA has hired to build new spacecrafts to fly astronauts to the International Space Station could face further delays that push certification of their vehicles to 2019, two years behind schedule, according to a report issued Thursday by government investigators. If that happens, NASA might be stranded, with no way to get its astronauts to the International Space Station, the Government Accountability Office said. In 2014, NASA awarded contracts to Boeing and SpaceX to develop vehicles that could restore the agency’s ability to put humans in space after the space shuttle was retired in 2011. Under the Commercial Crew program, Boeing was awarded $4.2 billion; SpaceX $2.6 billion. Since the shuttle was mothballed, NASA has had to rely on Russia to fly its astronauts to the station, an orbiting laboratory some 240 miles above Earth. NASA has bought seats with Russia through 2018, the report said. But there could be a problem if Boeing and SpaceX face further delays, because it typically takes three years to procure seats from Russia, the report said. “In order to avoid a potential crew transportation gap in 2019, the contracting process would have needed to start in early 2016,” the GAO said. It added that if “NASA does not develop a viable contingency plan for ensuring access to the ISS in the…more detail