The core stage development schedule for NASA’s Space Launch System (SLS) remains aggressive and any additional delays will threaten the program’s internal goal of launch readiness by September 2018, according to the Government Accountability Office (GAO).

GAO, in a report (GAO-16-612) released Wednesday, said the core stage development effort had approximately 50 days of schedule margin, or time within the schedule where activities can be delayed before affecting a key milestone. It said this key milestone is core stage delivery to Kennedy Space Center, Fla., to begin integrated operations with the Orion space capsule and Exploration Ground System (EGS) programs. The core stage functions as SLS’ fuel tank and structural backbone.

NASA and Orbital ATK performed their second SLS qualification motor test firing on June 28, 2016. Photo: Orbital ATK.
NASA and Orbital ATK performed their second SLS qualification motor test firing on June 28, 2016. Photo: Orbital ATK.

In addition, GAO said any delay in core stage development reduces schedule reserve for the whole SLS program. This is because the core stage is the program’s critical path, or the path of longest duration through the sequence of activities that determines the program’s earliest completion date. With only two months of schedule reserve remaining between the program’s internal goal and committed launch readiness date of November 2018, any reduction in program reserves threatens the committed launch readiness date.

GAO said that an independent review team responsible for reviewing SLS at each major program milestone found in 2015 that the core stage was unlikely to be able to support the SLS program’s committed date for launch readiness. This team, called the SLS Standing Review Board, cited a variety of reasons for this, including a steep learning curve for the handling and alignment of such a large structure and the potential for human access issues to avionics and propulsion once the stage is assembled.

The Standing Review Board also said an important event called the green run test carries risks because it is the first time both the cluster of four RS-25 engines will be fired and the first time the integrated engine and core stage auxiliary power units will be tested in flight-like conditions. The green test also carries risks, according to the board, because it will be the first time flight and ground software will be used in an integrated flight vehicle. The green run test is the culminating test of core stage development where the actual EM-1 core stage flight article will be integrated with the cluster or four RS-25 engines and fired for 500 seconds under simulated flight conditions.

Prime contractor Boeing [BA] and NASA told GAO they are working to establish additional margin within the core stage schedule, but whether the core stage stays on schedule is largely dependent on the success of the green run test. Boeing officials told GAO they originally had margin in their schedule for a second green run test if needed, but that it was removed due to the tight schedule.

GAO also found that the SLS program has not positioned itself well to provide accurate assessments of core stage progress because it has never had a performance measurement baseline for the core stage that is necessary to support full earned value management reporting. Earned value, or the planned cost of completed work and work in progress, can provide accurate assessments of project progress, produce early warning signs of impending schedule delays and cost overruns and provide unbiased estimates of anticipated costs at completion.

A SLS program official told GAO when the program and Boeing conducted its integrated baseline review, the program realized the contractor’s plans assumed synergies between the core stage and exploration upper stage efforts that would produce cost savings for the contractor, but NASA did not have the funding to begin this work under the same time frames identified by the contractor.

A SLS program official told GAO NASA asked Boeing to start replanning activities with a proposal that removed the exploration upper stage development from this contract action. GAO said NASA and Boeing in May signed the contract replan, with a cost increase of nearly $1 billion, from about $4.2 billion to about $5.2 billion. However, program officials told GAO it will probably be this summer before he program receives contractor earned value management data derived from the new performance baseline, some 4.5 years after contract award.

Without this information, GAO believes the SLS program has been in a poor position to understand the extent to which technical challenges with the core stage are having schedule implications or to the extent to which they may require reaching into the programs’ cost reserves.