A new report published Tuesday by NASA's inspector general looks into the development of a mobile launch tower for the agency's Space Launch System rocket.

The analysis finds that the total cost of constructing and modifying the structure, known as Mobile Launcher-1, is "at least" $927 million. This includes the original $234 million development cost to build the tower to support the Ares I rocket.

After this rocket was canceled in 2010, NASA then spent an additional $693 million to redesign and modify the structure for the SLS rocket. Notably, NASA's original estimate for modifying the launch tower was just $54 million, according to the report by Inspector General Paul Martin.

Mobile Launcher-1 supports the 355-foot-tall SLS rocket, provides access to the Orion spacecraft, and provides power, communications, coolant, and fuel to the rocket.

So why did it cost so much to modify the mobile launcher? The report places a lot of the blame on a cost-plus contract with a company named Vencore, which provided designs for ground support equipment. The company's contract started in March 2011, and NASA chose to not exercise Vencore’s final contract year option in 2017 due to the company's overall performance.

NASA not blameless

But the space agency is not blameless.

"NASA exacerbated these issues by accepting unproven and untested designs from Vencore in order to advance the construction and fabrication contracts," the report states. "Agency personnel stated that at times they knew the subsystem designs were not complete or needed more testing but advanced them because the project schedule required it so fabrication and construction activities could continue."

Ultimately, by accepting these unfinished designs, NASA experienced significant delays and costly rework for Mobile Launcher-1 project, which in turn created further delays and cost overruns.

Moreover, NASA did not use contractual mechanisms to punish Vencore for its poor performance. According to the inspector general, employees at Kennedy Space Center who rated Vencore’s performance "stated that even though design work was over budget and behind schedule they believed the contractor performed well due to the obstacles they had to overcome. As a result, Vencore received 'excellent,' 'very good,' or 'good' ratings despite the ML-1 project being significantly over budget and behind schedule."

NASA officials did something similar for award fees with the contract for the SLS rocket's core stage and its prime contractor Boeing. Critics have said the rocket is a make-work project for the space agency designed to maximize jobs rather than further exploration. The new report tends to support such criticism of a rocket originally planned to launch in 2017 but unlikely to fly before late 2021 at the earliest.

Now NASA is working on a second Mobile Launcher to accommodate the larger, Block 1B version of the SLS rocket. Bechtel won this contract to design and build the second larger mobile launcher for $383 million by March 2023. This would be for about one-third the cost of the first mobile launcher in half the time. Past performance would suggest this is unlikely.