NEW ORLEANS — Although NASA’s heavy-lift Space Launch System (SLS) will not fly often, it will fly affordably and safely, William Gerstenmaier, NASA’s top human spaceflight official, said here during a June 21 tour of the Michoud Assembly Facility, where the rocket’s core will be built.

The tour, attended by other NASA officials, local and state government representatives, and members of the media, also included a visit to the nearby Stennis Space Center in Mississippi. SpaceNews’ travel and lodging expenses for the two-day visit to New Orleans were paid for by Boeing, prime contractor for the SLS core stage.

Gerstenmaier, NASA’s associate administrator for human exploration and operations, was on hand not only to tour Michoud but also to mark the start of operations for the facility’s new Vertical Weld Center, a three-story machine — built by Boeing, Futuramic Tool and Engineering Co. of Warren, Mich., and PaR Systems of Shoreview, Minn. — that will weld aluminum alloy panels together to form the cylindrical segments of the 8.4-meter-diameter SLS core stage.

Using these and other tools, and an employee work force of “significantly less than 1,000,” NASA and Boeing could produce as many as two SLS cores a year, according to Patrick Whipps, the agency’s resident manager for Michoud. The machines unveiled by NASA June 21 are significantly more advanced than those used at the facility to build the space shuttle’s external fuel tanks, Gerstenmaier said. That means a leaner, comparatively cheaper manufacturing process.

“Typically, there were three or four or five different tools required to do the same job you’re seeing with one tool here,” Gerstenmaier told SpaceNews of the Vertical Weld Center. The tool not only welds SLS core segments together but allows engineers at Michoud to inspect the weld as soon as it is completed — something that during the space shuttle program would have required moving the hardware to another workstation.

For SLS, Boeing has “taken advantage of modern manufacturing, state-of-the-art things to try to lower our overall operating costs that makes this a very affordable rocket, even at low production rates,” Gerstenmaier said. 

Each SLS will be powered by four surplus space shuttle main engines, also known as RS-25s. NASA has 16 engines in storage at the Stennis Space Center. 

SLS is to make its maiden flight in 2017, when it will carry an empty Orion crew capsule to near-Moon space and back. Another flight would follow in 2021 and, depending on factors both technical and political, could see a crew of astronauts travel to a captured asteroid NASA wants to redirect to a high lunar orbit using a yet-to-be-built robotic spacecraft.

Notionally, SLS would next fly in 2025, giving the rocket a launch rate of once every four years. NASA has been spending about $1.8 billion a year on SLS development, including construction of a rocket test stand in Mississippi, and associated launch infrastructure at the Kennedy Space Center in Florida. Add in the cost of the rocket’s companion crew capsule, the Lockheed Martin-built Orion, and the tab rises to nearly $3 billion a year. 

Given the expense, and the enormity of the mission SLS has been charged with carrying out — NASA says the rocket is essential for one day launching humans to Mars — the low flight rate has raised red flags for some industry watchers, most recently during a June 19 congressional hearing on a draft NASA authorization bill.

“We have no experience with a human-rate flight system that only flies every two or three or four years,” NASA Advisory Council Chairman Steven Squyres told members of the House Space, Science and Technology Committee. “And I believe that’s cause for serious concern. It’s not just simply a matter of maintaining program momentum. It’s not even purely a matter of efficiency. It’s also a matter of keeping the flight team sharp and safe.”

Squyres has raised that point before, both in congressional testimony and before a National Academies panel charged with reviewing NASA’s human spaceflight program. 

Asked whether the rocket’s low flight rate raised concerns for either the safety of the crews who will ride it or the reliability of the vehicle itself, Gerstenmaier said “no.” 

“You may not see the extensiveness of the testing [with SLS] that you did with Apollo, but the testing is every bit as rigorous,” Gerstenmaier said, noting that the big rocket’s ongoing preliminary design review — a milestone in government development programs where a proposed design faces scrutiny from outside experts — is being informed by “a couple terabytes of data” gathered by engineers. 

Michoud’s mission

Michoud has had a hand in the space program since the beginning, building the core stage for the Saturn 5 rocket that powered the Apollo Moon exploration program and the external tank for the now-retired space shuttle, which flew 135 missions between 1981 and 2011. 

Like the canceled Constellation program, a Moon-return project conceived by the administration of former U.S. President George W. Bush, SLS will not employ nearly as many workers as the space shuttle program did.

Michoud is case in point. In the shuttle era, about 2,500 people worked at Michoud. Most were employed by Lockheed Martin, the prime contractor for the shuttle external tank and facility manager. The facility, managed since 2009 by Jacobs Technology Inc., now employs fewer than half that number. By way of comparison, there were about 10,000 people working at Michoud during the Apollo program, according to Whipps, NASA’s resident manager there. If NASA wanted to scale up SLS flight rates to the five, six or more a year that were common in the shuttle era, Michoud would need to hire more people and NASA would need to invest in more manufacturing tools. The Vertical Weld Center, Gore Weld Tool and Circumferential Dome Weld Tool that are there now could make two SLS core stage structures a year at most, Whipps told SpaceNews.

“It all depends on flight rate,” Whipps said. 

Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...