The OIG report lists several hardware interdependencies that could delay ground systems development, ultimately pushing back a November 2018 launch. For example, work on the Orion Service Module Umbilical, or OSMU, could be delayed while GSDO waits on connector plates that attach cables and hoses to Orion.

There were also issues raised with integration and testing schedules. The Mobile Launcher must be moved into the Vehicle Assembly Building for testing prior to the delivery of SLS and Orion. When it comes time to stack the rocket and capsule for the first flight, there may be a "learning curve," said the report, where engineers work through unforseen glitches.

Another potential problem is the completion of software used to prepare, monitor and launch SLS. The software package, called Spaceport Command and Control System, or SCCS, must be tested and validated before SLS and Orion make their way to pad 39B. SCCS controls everything from pumps and motors at the launch pad to displays inside the Kennedy Space Center firing room.

"Historically, software development efforts have been a source of significant cost and schedule overruns, and the complexity and highly interdependent nature of the GSDO effort combine to make software development one of the greatest risks to on-time and on-budget performance of the Program," the report said.