GAO: SLS Making Progress, Major Milestones Lie Ahead

Space Launch System with Orion capsule. (Credit: NASA)

When Congress insisted that NASA build the Space Launch System (SLS) some years back, the argument was simple: just adapt all this technology  from the space shuttle program using the workers and infrastructure that already exist to develop a new heavy-lift booster.

It all sounded deceptively simple — and deceptive it was. NASA and its contractors soon ran into a problem that affects many such projects: it’s often easier to build something from scratch than to modify systems that already exist. And there you have the problem with the SLS program in a nutshell.

The recent Government Accountability Office assessment of program bears this out. Take the system’s core stage, which is derived from the space shuttle’s external tank. (Emphasis mine)

“According to program officials, the liquid hydrogen tank has proven difficult to weld to specifications because it is thicker than metals that have been used by industry in the past,” the GAO found. “Without a history of similar efforts to compare to, officials explained that they have to check and test every potential anomaly with increased scrutiny than if they were producing something already used throughout the aerospace industry.”

The core stage also contains four space shuttle engines, something the external tank never possessed. NASA plan to conduct a 500-second test firing with all four engines integrated into the stage has some unique challenges.

“This test will stress the flight components as well as the ground equipment used for the test,” the GAO report stated. “For example, according to program officials, 7 of the 12 cryogenic fluid pumps at Stennis Space Center must work together in order to fuel the vehicle.

“Should issues arise, the program will likely need additional time to assess and mitigate difficulties or glitches, which would likely affect delivery to Kennedy Space Center and could delay the enterprise integration and test schedule,” the report added.

NASA is working toward a December 2019 launch date for Exploration Mission-1, which will launch SLS on its maiden flight an an automated Orion spacecraft into deep space. However, the flight is likely to slip to June 2020.

The GAO’s assessment of the SLS program is below.

NASA: Assessments of Major Projects
Government Accountability Office
May 1, 2018
Full Report

Space Launch System

The Space Launch System (SLS) is intended to be NASA’s first human-rated heavy-lift launch vehicle since the Saturn V was developed for the Apollo program. SLS is planned to launch NASA’s Orion spacecraft and other systems on missions between the Earth and Moon and to enable deep space missions, including Mars.

NASA is designing SLS to provide an initial lift capacity of 70 metric tons to low-Earth orbit, and be evolvable to 130 metric tons, enabling deep space missions. The 70-metric-ton capability will include a core stage, powered by four RS-25 engines, and two five-segment boosters. The 130-metric-ton capability will use a new upper stage and evolved boosters.

Project Summary

In December 2017, NASA announced a new schedule and cost estimate for the SLS program, after determining that the November 2018 launch readiness date for Exploration Mission-1 (EM-1) was no longer feasible. NASA is now planning to an internal launch readiness date of December 2019, with 6 months of schedule reserve to a June 2020 date. The life-cycle cost estimate for SLS is approximately $9.7 billion to the December 2019 date and $9.8 billion to the June 2020 date.

The delivery schedule for the program’s core stage — which functions as the SLS’s fuel tank and structural backbone—has continued to slip as the program addresses a series of technical challenges, including the completion of welding its large, first stage. The program currently has no schedule reserve to ship the core stage for testing, as well as from the test site to the launch site, in order to meet the December 2019 launch readiness date. Should problems or issues arise during testing, they will likely affect the enterprise integration and test schedule.

Cost and Schedule Status

Credit: GAO

In December 2017, NASA announced a new schedule and cost estimate for the SLS program, after determining that the November 2018 launch readiness date for Exploration Mission-1 (EM-1) was no longer feasible. In April 2017, we found that the date was likely unachievable for all three human spaceflight programs—Exploration Ground Systems, SLS, and Orion Multi-Purpose Crew Vehicle—due to technical challenges continuing to cause schedule delays and the programs having little to no schedule reserve to the EM-1 date, meaning they would have to complete all remaining work with little margin for error for unexpected challenges that could arise.

Credit: GAO

The new internal launch readiness date for EM-1 is now December 2019, but NASA has also allocated 6 months of schedule reserve to June 2020 for possible manufacturing and production schedule risks. This represents a delay of 13-19 months for EM-1. The life-cycle cost estimate for SLS is about $9.7 billion to the December 2019 date and $9.8 billion to the June 2020 date, or 0.4 to 1.5 percent above the project’s committed baseline.

Technology, Design, and Manufacturing

The delivery schedule for the program’s core stage — which functions as the SLS’s fuel tank and structural backbone — has slipped 14 months in the last year to May 2019, due in large part to production issues that have delayed completion of the core stage element.

According to program officials, the liquid hydrogen tank has proven difficult to weld to specifications because it is thicker than metals that have been used by industry in the past. Without a history of similar efforts to compare to, officials explained that they have to check and test every potential anomaly with increased scrutiny than if they were producing something already used throughout the aerospace industry.

In addition, according to officials, because this is the first flight article, the contractors are performing extensive testing to ensure that their production processes and methods are resulting in end items that meet or exceed specifications so that the next unit can be produced more quickly.

In addition to these issues, the program has faced work slowdowns and stoppages due to severe weather. In February 2017, a tornado hit parts of the Michoud Assembly Facility in Louisiana, where the core stage is being produced. While work resumed shortly after the storm, according to program officials, it did so at less than full capacity and delayed the program by a total of about 2 months. According to officials, repair work is complete in SLS manufacturing areas and should not further impact production work at the facility.

Integration and Test

The program has no schedule reserve through delivery of the core stage to Kennedy Space Center for the December 2019 launch date. In addition to completing production of flight and test articles, the program has to integrate the engines to the core stage and ship them to Stennis Space Center for a green run test. During this test, the core stage is fueled and the four main engines fired for about 500 seconds for the first time.

This test will stress the flight components as well as the ground equipment used for the test. For example, according to program officials, 7 of the 12 cryogenic fluid pumps at Stennis Space Center must work together in order to fuel the vehicle. Should issues arise, the program will likely need additional time to assess and mitigate difficulties or glitches, which would likely affect delivery to Kennedy Space Center and could delay the enterprise integration and test schedule.

Project Office Comments

In commenting on a draft of this assessment, SLS program officials stated that a vast majority of SLS development and production work is on track for EM-1 and that work is also proceeding for the first crewed flight—EM-2. In addition, officials state that the program is successfully working through first-time production issues that are not unprecedented for a program of this scope and ambition. Program officials also provided technical comments, which were incorporated as appropriate.