On a tour of the Aerojet Rocketdyne assembly building at NASA’s Stennis Space Center in southern Mississippi, site manager Mike McDaniel stops at a double row of shrouded shapes and big white metal boxes inside a garage-like room. In each is an RS-25, the space shuttle’s main engine. With the exception of one more engine to be assembled from spare parts, the room we’re standing in holds the entire world supply—15 in all—of flight-proven, reusable big booster engines. While the value is hard to calculate, given that production lines for replacement engines haven’t restarted, there’s certainly more than a billion dollars’ worth of hardware tucked into a space no bigger than a 7-Eleven.
The engines are critical to NASA’s next plan for human spaceflight and illustrate an important principle guiding the design of the nation’s next booster: Rather than reach for advances in rocketry, engineers are to use proven technology. The RS-25 engines, which performed almost flawlessly during 135 shuttle launches, are a gold standard for reliability and power that NASA wants to preserve, even after the small inventory is used up. Yet the last enhancement to the engines was made in the 1990s, and the new launch vehicle—uninspiredly named the Space Launch System—is expected to be the first one capable of sending humans beyond the moon. The contradiction between its design constraint and its ambitious mission puts engineers like McDaniel in a tough spot. They are using space shuttle hardware for a vehicle tasked with a human spaceflight mission far more daunting than putting astronauts in orbit around Earth. But you won’t hear complaints at Stennis, where the engines are tested, or at Marshall Space Flight Center in Huntsville, Alabama, where the SLS program is managed.
“We had a school group in here one day to see the engines, and a girl raised her hand,” McDaniel recalls. “She said, ‘There are supposed to be 15 here but I only count 14.’ That’s the kind of person we want in this program, who doesn’t take things for granted.”
Little is taken for granted with the SLS, given the fate of its predecessor, the more imaginatively named Ares I rocket, which didn’t get very far. Ares made a single test launch in 2009 before the Obama administration cancelled the human exploration program—Constellation—which required a big new launch vehicle for missions to the moon. But the SLS borrows certain features from the Ares I rocket, including a new digital engine controller and the use of shuttle-era solid rocket boosters.
NASA and Congressional supporters are determined to have the Space Launch System ready for its first launch in December 2017, seven years after NASA got its orders from Congress to build a new heavy-lift rocket for deep space. At a glance, the rocket will have a classic profile, reminiscent of a launcher even older than the space shuttle: the Saturn V. Like Saturn, each SLS booster will fly just once, then be discarded. In its first phase, the launch vehicle will have a payload capacity of 77 tons and stand 321 feet—not quite as tall as the Saturn V but delivering 10 percent more thrust. It will grow through the 2020s to support missions that will be gradually more ambitious. The final version, called Block II, will tower nearly 400 feet on the Mobile Launch Platform—40 feet taller than the Saturn V, with 20 percent more thrust. Capable of carrying 143 tons to low Earth orbit or a crew to Mars, it will be the most powerful rocket ever built.
As with the Saturn, the SLS will be topped with a conical capsule for manned flight, called Orion (see “America’s Next Spaceship,” Aug. 2014). But down lower, the Space Launch System has more visibly in common with the space shuttle, with two solid rocket boosters strapped to its sides. The rocket’s first stage (which NASA calls the core) is a stretched version of the shuttle’s external tank and has the same diameter, so that shuttle-era tooling can be reused. At the base of the core are four space shuttle main engines (SSMEs). It will use a single upper stage to boost Orion into deep space.
A number of technologies that hadn’t been developed when the shuttle was designed, such as stir-friction welding for the SLS core and 3D printed parts for Orion, does push the SLS beyond the shuttle’s world. “This is brand-new, modernized equipment, resulting in much more reliability and capability at much less cost,” says Charlie Precourt, a former shuttle commander and today vice president and general manager of ATK, the solid booster manufacturer. At ATK, he says, workers are adding a fifth segment to give the solid rocket booster more capability. Precourt says the work will be done using only one-fourth the number of employees required during the shuttle era.
A multi-purpose, disposable vehicle, the SLS is sure to be expensive, but just how expensive is not yet known. Boeing is building two core stages under a $2.8 billion contract. According to budget documents, the SLS program annual cost is less than half that of the shuttle program, which ran to $4 billion annually in its last years. But the shuttle flew successfully 133 times over three decades, and (barring some political sea change) the SLS isn’t expected to launch more often than once every two years. The Government Accountability Office estimated the SLS’s cost through the first launch at $12 billion, and the total tab through 2020 at $22 billion. But in July, the GAO warned that NASA would miss the 2017 launch unless the SLS program gets an additional $400 million.
The first SLS mission is a test. It will send an unmanned Orion capsule looping far around the moon, then back to Earth for a splashdown. The second mission? Less firm. While some House members are urging that the second mission send a robot probe to explore Jupiter’s moon Europa, which may harbor life beneath its frozen surface, NASA’s current plan is to carry astronauts to visit an asteroid orbiting the moon. (A separate robot spacecraft would go out first, grab the rock, and haul it into lunar orbit.)
Critics like former NASA deputy administrator Lori Garver see the SLS as a red-tape-ridden reminder of Old Space from top to bottom. By the time NASA uses the SLS to go to Mars, Garver has said, astronauts will be going there on “50-year-old technology.” New Space could do better, she and others, like Congressman Dana Rohrabacher of California, say, pointing to newcomers like Elon Musk’s Space Exploration Technologies (SpaceX), which has used its Falcon 9 rocket for low-cost launches of cargo to the International Space Station and satellites to high orbits.
SpaceX is already planning a heavy-lift Mars-capable rocket that would rely on a radically more powerful and sophisticated engine called Raptor, which would burn liquid methane rather than the standard hydrogen or rocket-grade kerosene. It’s a bit of a long shot for Musk; SpaceX has never built an engine so powerful or efficient, nor has any nation’s space program put methane-fueled rocket engines into production.
SLS managers don’t have the time or the money to pursue exotic technologies or big leaps like methane-fueled engines. To be fair to the pocket-protector crowd, it’s not for lack of far-out thinking. NASA archives hold heaps of plans for cool gadgets like an aerospike engine and nuclear-thermal rocket. Today’s dialogue is less about innovative gizmos and more about how space spending has become a zero-sum game, to the point that even strong space advocates have divided into bitter factions, fussing yearly over whatever scarce dollars are available.
There are three camps. The first puts their hopes in the traditional NASA/contractor partnership and supports the NASA-designed SLS as the best way to keep the man-in-space dream alive. This is championed by a majority in Congress. The second is led by President Obama and charismatic business leaders like SpaceX’s Musk, who believe that the private sector should take the lead role in building and flying boosters for manned space, first into low orbit, and eventually to Mars. The third worries that the traditional “bucks for Buck Rogers” focus on human-rated boosters for the space station and Mars is draining the lifeblood from scientifically productive work, such as a robotic mission to Europa. Although cheaper than any human-led alternative, such one-off robot missions still cost billions and take years to develop. And, depending on the location, also take years to deliver.
NASA still has visionaries in its ranks, and their eyes are on the SLS. “We’ve been spending all our time in low orbit. That’s just 220 miles up,” says Chris Crumbly at Marshall, who is in charge of lining up scientific missions for the SLS’s early years. Crumbly says that an SLS-boosted mission would get to Europa in just two years, rather than the seven an Atlas V rocket would require. Missions now cruising deep space, such as New Horizons on its way to Pluto, had to pare back on payload because their launchers simply couldn’t haul any more weight.
But using the SLS for missions to the outer worlds, or in fact anywhere in deep space, will require deep pockets. “The problem with the SLS is that it’s so big—that makes it very expensive. It’s very expensive to design. It’s very expensive to develop,” former Mercury, Gemini, and Apollo flight control chief Chris Kraft told the Houston Chronicle last year. “When they actually begin to develop it, the budget is going to go haywire.” The SLS, though, has powerful supporters in Congress, such as Senators Richard Shelby of Alabama and Bill Nelson of Florida. Shelby told the Huntsville Times last year that he would “continue to fight hard to ensure that taxpayer dollars are invested wisely in SLS so that we maintain our nation’s leadership role in human spaceflight.”
As NASA sees it, the SLS is precisely the sort of vehicle the country needs post-shuttle, for a variety of missions. “We’re not building a one-of-a-kind spacecraft,” says William Gerstenmaier, NASA associate administrator for human exploration and operations. “We’re building hardware that can satisfy multiple needs. There’s real work moving forward. This is no longer a paper program.”