NASA Human Space Exploration: Delay Likely for First Exploration Mission, Report to Congressional Committees [open pdf - 3MB]
"NASA is undertaking a trio of closely related programs to continue human space exploration beyond low-Earth orbit: the SLS [Space Launch System] vehicle; the Orion capsule, which will launch atop the SLS and carry astronauts; and EGS [Exploration Ground Systems], the supporting ground systems. NASA's current exploration efforts are estimated to cost almost $24 billion--to include two Orion flights and one each for SLS and EGS--and constitute more than half of NASA's current portfolio development cost baseline. All three programs are necessary for EM-1 [exploration mission one] and are working toward a launch readiness date of November 2018. In a large body of work on this issue, including two separate July 2016 reports, GAO [Government Accountability Office] has found that these programs have a history of working to aggressive schedules. The House Committee on Appropriations report accompanying H.R. 2578 included a provision for GAO to assess the acquisition progress of the Orion, SLS, and EGS, programs. This report assesses the extent to which these programs have risks that affect their progress toward meeting their commitments for EM-1. To do this work, GAO assessed documentation on schedule and program risks and interviewed program and NASA officials."
Government Accountability Office: http://www.gao.gov/