Since Aug. 17, NASA’s massive Space Launch System (SLS) moon rocket has stood silent on pad 39B at the Kennedy Space Center, towering over the Florida swamps. By any measure it’s a beautiful machine; by any measure it’s a promising machine; and by any measure it’s been a troubled machine—especially over the past two weeks. On Aug. 29 and again on Sept. 3, the rocket’s six engines were supposed to light, generating a record 8.8 million lbs. (4 million kg) of thrust, muscling the hardware stack off the pad and hurling it toward space. Had things gone according to NASA’s plans, the SLS’s Orion crew capsule would be in the early stages of a mission to the moon by now. The space agency’s Artemis program, which aims to have American astronauts back on the lunar surface by 2026, would have officially kicked off.
But that hasn’t happened yet. Both planned launches were scrubbed. The first was called off after being plagued by a handful of problems—the worst of them a faulty sensor that falsely indicated that one of the main engines had failed to be cooled sufficiently for ignition. A lack of proper cooling could have led to the engine bell cracking or the engine itself shutting down. The second was halted by a liquid hydrogen leak that prevented the rocket from being fueled properly. Engineers are now fixing the fuel leak problem on the launch pad, but will likely have to roll the rocket back to its Vehicle Assembly Building hangar to recharge batteries that have drained during the long wait on the pad, and check for other potential leaks. That will push the inaugural launch until sometime in October at the earliest.
“We’ll go when it’s ready. We don’t go until then,” said NASA Administrator Bill Nelson in a statement to the press after the second stand-down. “This is part of our space program: Be ready for the scrubs.”
Scrubs and disappointments notwithstanding, there is no overstating the scale and ambition of the SLS. Until now, the Apollo program’s Saturn 5 held the record for the most powerful rocket ever launched. When its five engines first lit on Nov. 9, 1967, they produced 7.5 million lb. (3.4 million kg) of thrust, rattling the windows in the TV press booths and causing plaster dust to flutter down from the ceiling of the nearby launch control center. Over the course of the following five years, nine Saturn 5s launched crews of astronauts to the moon.
The SLS is a bigger beast, and it needs to be. All of that propulsive power is required to launch the larger crew capsule and other payloads required for a return-to-the-moon program that will not only send astronauts moonward to explore the lunar surface for a few days at a time, but will also later be used to launch crews who will set up a permanent presence there. Camping out on a celestial body that’s only three days from home is seen as an essential first step to learning how to live off the extraterrestrial land—a critical rehearsal for later journeys to Mars which, at minimum, is an eight-month trip each way.
“The SLS is the start of a generational effort to return us to deep space and keep us there,” says John Honeycutt, NASA’s SLS program manager. “It has got tremendous capability.”
But the SLS had a long history and a challenging future even before its recent launch woes. It has taken 18 years to get a new moon rocket built, at a cost so far of $23 billion just from 2012 to 2022 and a per-launch price tag of $4.1 billion, according to a 2021 report by NASA’s Office of the Inspector General. “Relying on such an expensive, single-use rocket system will, in our judgment, inhibit if not derail NASA’s ability to sustain its long-term human exploration goals to the moon and Mars,” Inspector General Paul Martin told told Congress in March.
That warning is especially persuasive in an era in which the private sector is competing with NASA to bring down per-launch costs and, regarding SpaceX, safely land and reuse boosters, rather than simply throwing them away after a single use—as was done with the Saturn 5 and remains the case with the SLS.
“The architecture we’ve chosen doesn’t allow for reusability,” says Jim Free, NASA’s associate administrator for exploration systems. “Disposing of it is the best way to go, and that’s what we’ve chosen.”
Even with those shortcomings, the SLS is a huge and remarkable machine, and the one on which NASA has placed its bet for the future of human space exploration. The first flight—whenever it happens—will help determine if that bet will pay off.
A Long, Strange Trip
The roots of the SLS go back to Jan. 14, 2004, when then-President George W. Bush announced that the space shuttle fleet would be retired. In its place, NASA would build a new heavy-lift rocket and crew capsule for missions to the moon and later to Mars.
Skeptics dismissed the move as little more than a bit of election-year candy, designed to appeal to NASA-heavy constituencies in Texas, Bush’s home state, and Florida, the swingiest of swing states, which gave Bush the presidency by a razor-thin margin in the 2000 election. But Bush meant business, and the money began flowing for a moon rocket that would be dubbed Ares V, with plans to have astronauts back on the moon by 2015.
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Rather than being designed from scratch as the Saturn 5 was, the Ares V would be made at least partly from off-the-shelf components. Its core stage—the backbone, and largest section, of the rocket—would be powered by six RS-68 engines—the same engines used by the private-sector Delta IV rocket. Flanking the core stage would be two solid rocket boosters borrowed from the space shuttle program. The rocket’s second stage—which sits atop the first—would be a newly designed, upgraded version of the Saturn 5’s second stage. This would boost an Apollo-like Orion crew capsule the rest of the way to space and out toward the moon after the core stage exhausted its fuel and was jettisoned. Bush proposed to pay for the entire program, which was called Constellation, by reallocating $11 billion from NASA’s cumulative five-year budget of $86 billion—a bargain, as space hardware goes.
But things didn’t work out that way. By the time the Bush Administration left office in 2009, the Constellation program was grossly over budget and behind schedule—with a Government Accountability Office report that year revealing that a return to the moon, and a follow-on mission to Mars, would, by NASA’s own estimates, cost $230 billion by 2025. Incoming President Barack Obama summarily canceled Constellation.
But Congress pushed back. In the summer of 2010, Nelson was a Democratic senator from Florida, and chairman of the Senate’s space subcommittee. With less than 24 hours left before Congress’ August recess, the Senate had unanimously approved authorization for a massive new rocket that would replace Ares V, keeping NASA’s dream of deep-space travel alive and, not incidentally, providing a wealth of jobs for the engineers and other workers who would build the new machine. It was up to Nelson to convince Steny Hoyer—then, as now, Democratic Majority Leader of the House of Representatives—to pass the bill in the House.
As Nelson recalls it today, Hoyer was none-too-pleased at the last-minute arm-twisting from the upper chamber of Congress. “He was cussing at me,” Nelson recalls. “He told me, ‘I don’t like it that the Senate always makes the House take your position at the last minute. I don’t have time to take it up.’” Hoyer nonetheless agreed to try, and not long before midnight, the rocket passed the House easily, with over three-quarters of the chamber’s members voting aye.
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The new heavy-lift rocket was given the prosaic name SLS to signal practicality, and the promise of a price reduction. Obama was under pressure from both Capitol Hill and the private sector, which, like Nelson, was mindful of the jobs the SLS and Orion would provide, and so he went along—on the condition that costs would come down.
That required a major redesign of the SLS. First, the new second stage would be done away with. In its place would go a proven—and existing—upper stage already used by the Delta IV, to be purchased from private manufacturer United Launch Alliance. The six main engines on the core stage would also be scrapped. Instead, NASA would go with engines it already had: the same main engines that the space shuttle used. With the shuttles scuttled, the in-stock engines were merely gathering dust.
“There were 18 main shuttle engines already in the pipeline,” says Free. “So using them saves money.” The shuttle-derived solid rockets flanking the core stage would be retained from the Ares V, contributing to the muscle the shuttle’s main engines would provide, and rounding out the rocket’s overall 8.8 million lb. of thrust.
To the Moon
The mission that NASA hopes to fly in October—dubbed Artemis 1—will be a 42-day affair that will see the Orion spacecraft make two wide loops around the moon, before returning home and splashing down in the Pacific Ocean off the coast of San Diego. As NASA currently plans things, Artemis 2 will follow in 2024, with four astronauts making a shorter, ten-day circumlunar mission, flying 4,600 mi. (7,400 km) beyond the far side of the moon—though not going into lunar orbit—and then returning home. Artemis 3, the first lunar landing of the Artemis program, will follow in 2025 or 2026.
In order for astronauts to set foot on the moon, they need not just an SLS to get them into space and an Orion spacecraft to put them in lunar orbit, but also what NASA calls a Human Landing System (HLS)—a spacecraft like the Apollo lunar module, capable of descending to the moon’s surface. In April 2021, NASA selected SpaceX to provide the HLS in the form of the company’s Starship spacecraft, a 164-ft. (47 m) stainless steel craft that will be launched aboard SpaceX’s new Super Heavy booster. Starship will fly out to the moon uncrewed, where it will rendezvous with the astronauts aboard Orion. Two of the four crewmembers will then fly the HLS down to the surface, while the other two remain in lunar orbit aboard Orion. The pair of moon walkers will remain on the surface for six and a half days, then blast back off, rendezvous again with Orion and fly back home. The abandoned Starship will eventually be disposed of in a permanent orbit around the sun.
That’s the plan, at least, but thus far, a crew-rated Starship spacecraft has not even been built, much less tested in space. Nelson professes to have few concerns, pointing to SpaceX’s multiple crew launches to the International Space Station, as well as the 173 successful launches of its workhorse Falcon 9 rocket, serving both the government and the private sector.
“Look at the success of SpaceX,” Nelson says. “[The company] is on track for all of what NASA calls milestones. … They’ve had phenomenal success.”
Even if SpaceX does prove capable of delivering the goods, there’s still the matter of money—despite the supposed cost-cutting redesign. Here too, Nelson is sanguine, insisting that as NASA ultimately launches what it hopes to be one SLS per year, the price will be slashed “dramatically,” as he puts it—though he does not cite a dollar figure.
The lion’s share of the savings Nelson cites should come from the simple fact that research and development costs will no longer be included in the overall price tag; with that design and testing work complete, the rockets could be built faster, too. What’s more, NASA is already in discussions with prime contractors Boeing and Northrop Grumman for moon missions extending as far as Artemis 9, with an option to extend that deal to Artemis 14. Building and flying in bulk could also help cut costs.
But not everyone is on board. “This reminds me of the arguments that were made at the beginning of the shuttle era, that with repeated launches the cost would come down. That never happened,” says John Logsdon, professor emeritus and founder of the George Washington University Space Policy Institute. That said, he agrees economies of scale could lower the cost of future launches. “It makes sense that the cost will come down,” he says, “but it may not be by very much.”
Pricey or not, the SLS is NASA’s ride of choice for this decade and beyond. And the space agency will have more disposable cash come 2030, when the Space Station is deorbited—freeing up the $4 billion per year it costs the U.S. to operate and maintain it. That should make it easier for NASA to make good on its near-term moon plans as well as its longer-term Mars plans. More than half a century after the first moon landings, the U.S. remains committed to making human beings a multi-world species. We are counting on the SLS to start that journey.
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