Those 15 SSMEs at Stennis are the most significant pieces of hardware that have helped the SLS move quickly beyond the paper stage. They were tested and improved throughout the 30 years the space shuttle flew. The first-generation SSMEs were “early in staged-combustion, and we were very close to the material limits on everything,” says NASA’s Mike Kynard, who recently retired as manager of liquid engines for the SLS at the Marshall Space Flight Center.
The engines that replaced the original models are more powerful. “At one million seconds [of run time] and 3,000 starts, we know it up one side and down the other,” he says. With turbopumps operating at 37,000 rpm, each turbine blade in the pump—though no bigger than a postage stamp—has to produce 600 horsepower. As reusable engines with proven durability, they would have been capable of supporting many more shuttle launches, but on the SLS, these high-performance machines will be used just once then dropped into the Atlantic with the rest of the core stage and the strap-on boosters. (Unlike in the shuttle era, the strap-ons won’t be reused.)
“It’s a misuse of those engines,” says J.R. Thompson, a former director of Marshall who went on to head Orbital Sciences Corporation, which also delivers cargo to the space station. Thompson, now retired, was a key manager during the early years of SSME development—a soul-trying period that saw 13 engines burn up or blow up during ground tests before 1983. “I am not a fan of SLS,” he tells me over breakfast in Huntsville. “It has no mission. It costs way too much. It’s driven by political decisions. It’s a job program. In my view, there’s no enthusiasm in the country for it.”
One private nonprofit is trying to boost enthusiasm for the SLS as the most practical way to reach Mars soonest. The Inspiration Mars Foundation asked NASA to aim for a 2021 launch window. “It’s a good thing the SLS is being developed,” says Taber MacCallum, the foundation’s chief technology officer. “I didn’t frankly start off as an SLS supporter in this, and I came around to being one.”
Both Stennis and Marshall space centers are all in. Other engines besides the flight-ready SSMEs will play a part in preparations for the Space Launch System’s first launch. One that Stennis facility director Mike McDaniel shows me in the hall is a non-flight SSME to be used for ground tests this fall. The point of those tests will be to prove out the new digital engine controller. At Marshall, engineers show me that particular piece of gear in the Hardware Simulation Laboratory. An engine controller is a suitcase-size computer that nestles alongside each engine, monitoring vital signs and tweaking valves, and generally keeping the engine from the point of self-destruction.
On our walk-through of the lab, deputy liquid-engine manager Tom Byrd points out the grayish, original controller from the shuttle era; it used the same processor as an Apple IIe computer. The new controller has modern electronics because it was developed in 2009 for Constellation-Ares. It’s also half the weight and half the cost of the old one. NASA is in the
process of moving tests for it from the safe confines of the Hardware Simulation Laboratory to Stennis’s Test Stand A-1 in order to ensure the electronics will work under heat, noise, and vibration.
Byrd, who joined NASA in 1983 and retired last summer, watched the Constellation program founder, and now sees the SLS as critical to NASA’s future and to the aerospace industry at large. “Within five years, we’ll have thousands of people eligible to retire from NASA. It’s a huge number, about 40 percent of the workforce. So we need a lot of replacements, and they need a flagship program to sink their teeth into,” he says, echoing J.R. Thompson’s opinion of the SLS as a jobs program.
At Stennis, in less than two years, a derrick crane atop the otherworldly complex called B Stand will whir to life. It will swing over an adjacent canal, pluck the SLS core off a barge arriving from Louisiana’s Michoud Assembly Facility, raise it several hundred feet in the air, and inch it down to a very stout fitting. Propellant tanks will be filled to the brim, bolts will be tightened, and NASA will be ready to light the four SSMEs at the bottom of the core for a full-duration burn of nine minutes. If this test goes well, the core will then travel by barge to Florida and join up with solid rocket boosters and the upper stage for a debut at Kennedy Space Center’s Launch Complex 39B a year later.
While B Stand is rarely photographed from the shady north side, that angle offers the most striking view. On the outside corners are four flared concrete legs the size of skyscrapers that frame an even larger concrete core. A multitude of girders and thick steel plates brace the engine and channel air flow. There are two stands: B-1 to the west, and B-2 to the east. Underneath each engine mount is a gigantic gray scoop a hundred feet high that tops off at ground level. This is the flame bucket: Every second, 5,000 gallons of water will inundate the area and flow down the bucket to keep the steel from melting under the hydrogen flame. B Stand is a National Historic Landmark because its full-throated, multi-engine booster tests were key to both Apollo and the shuttle. Testing began in 1967, and since then its mission can be summarized this way by engineer Bryon Maynard: “We’d rather make our mistakes here than at KSC. That’s why we test.”
While that core-stage test won’t include the solid rocket boosters, it will be powerful enough to make NASA spend hundreds of millions for a full rehab of B-2—cutting out rusty parts, yanking leftovers from previous tests, and bringing old electronics into the 21st century. As we make our way past a dark corridor called Damnation Alley, Maynard tells me he found graffiti dating to Apollo in control rooms. It’s not hard to get my group of guides talking about the good old days, even those who were too young to participate. “I was watching Mercury on TV at five years old,” says Rick Rauch, lead engineer on the stand restoration. “I knew right then what I wanted to do. I joined NASA in 2000, so it took a while to get here.”
The test stands at Stennis are adaptable to engines big and small, whether of traditional or radical design. One might say that rocket engineers come here in peace for all mankind, even when employed by companies that used D.C. lobbyists to scramble for space dollars. Here rocketeers share the universal language of pragmatism: What breaks and why? What holds up at max power and beyond? How do you know?
Not far from where the SLS engines are tested, Stennis is hosting SpaceX engineers who are checking components for its methane-fueled Raptor. I’m reminded of the manner in which warring tribes of the Great Plains laid down their weapons periodically and gathered at an outcropping of pipestone rock in present-day southwestern Minnesota, where they quarried the soft red stone for spiritual ceremonies back home.
A half-mile from Stennis’ Test Stand A-2, I’m watching a test of what may be the future for the SLS: the Aerojet Rocketdyne J-2X engine planned for use on the SLS’s upper stage. In the last year, NASA has had to shelve development of the engine; it’s being used here only to test the engine controller. The J-2X may yet fly on the SLS, but for the first flight at least, NASA plans to use a cryogenic upper rocket stage, powered by the Aerojet Rocketdyne RL10, which was used on United Launch Alliance’s Delta IV booster.
“Our goal is to bring engine costs down by half, but [retain] the same performance and reliability,” says Mike Kynard. “It’s a budget-constrained environment, so we can’t make wholesale changes. We’ll have to choose between options.”
As the count drops to zero, a mighty flow of water is raising a Niagara-like mist. Through binoculars, the base of Test Stand A-2 has the look of a dam spillway, but it’s part of the flame handling system. Engineer Bryon Maynard taps his wrist: almost time. We check our hearing protection. There’s a wave of chest-thumping noise that shakes the steel railings and decks of our perch. Propelled by blue-white fire, clouds billow from the rocket engine and move north. At 150 tons of thrust, the J-2X engine mounted in the stand, if unleashed, would heave three loaded semi-trailers into the air.
NASA will need that much power if it ever decides to evolve the SLS into its largest configuration for trips to Mars. Meanwhile, the biggest problem for the SLS is less technical than political: In the coming decades will there be enough politicians willing to support such an expensive space beast? Or will historians eventually class it with the one-flight Soviet shuttle Buran? Will the SLS be reserved for politically charismatic missions such as putting boots on Mars, or can it boost robot voyages as well? With the first crewed mission not expected before 2021, there’s time to work out mission goals and the manifest. If the schedule and the will hold, NASA will have something it’s never had before—a system capable of slinging humans, habitats, and robot explorers far beyond the moon and into deep space.