NASA’s Space Launch System Will Lift Off – IEEE Spectrum

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But with rival rockets readying for flight, the value of SLS is murky
Last October, an Orion spacecraft was mounted atop the Space Launch System.
Inside the Vehicle Assembly Building (VAB) at NASA’s Kennedy Space Center in Florida—a cavernous structure built in the 1960s for constructing the Apollo program’s Saturn V rockets and, later, for preparing the space shuttle—the agency’s next big rocket is taking shape.
Tom Whitmeyer, NASA’s deputy associate administrator for exploration system development, recalled seeing the completed Space Launch System (SLS) vehicle there in October, after the last component, the Orion spacecraft, was installed on top. To fully view the 98-meter-tall vehicle, he had to back off to the opposite side of the building.
“It’s taller than the Statue of Liberty,” he said at an October 2021 briefing about the rocket’s impending launch. “And I like to think of it as the Statue of Liberty, because it’s [a] very engineering-complicated piece of equipment, and it’s very inclusive. It represents everybody.”
Perhaps so. But it’s also symbolic of NASA’s way of developing rockets, which is often characterized by cost overruns and delays. As this giant vehicle nears its first launch later this year, it runs the risk of being overtaken by commercial rockets that have benefited from new technologies and new approaches to development.
NASA’s newest rocket didn’t originate in the VAB, of course—it began life on Capitol Hill. In 2010, the Obama administration announced its intent to cancel NASA’s Constellation program for returning people to the moon, citing rising costs and delays. Some in Congress pushed back, worried about the effect on the space industry of canceling Constellation at the same time NASA was retiring its space shuttles.
The White House and Congress reached a compromise in a 2010 NASA authorization bill. It directed the agency to develop a new rocket, the Space Launch System, using technologies and contracts already in place for the shuttle program. The goal was to have a rocket capable of placing at least 70 tonnes into orbit by the end of 2016.
To achieve that, NASA extensively repurposed shuttle hardware. The core stage of SLS is a modified version of the external tank from the shuttle, with four RS-25 engines developed for the shuttle mounted on its base. Attached to the sides of the core stage are two solid-rocket boosters, similar to those used on the shuttle but with five segments of solid fuel instead of four.
Difficulties pushed back the first SLS launch by years, although not all the problems were within NASA’s control.
Mounted on top of the core stage is what’s called the Interim Cryogenic Propulsion Stage, which is based on the upper stage for the Delta IV rocket and is powered by one RL10 engine, a design that has been used for decades. This stage will propel the Orion capsule to the moon or beyond after it has attained orbit. As the name suggests, this stage is a temporary one: NASA is developing a more powerful Exploration Upper Stage, with four RL10 engines. But it won’t be ready until the mid-2020s.
Even though SLS uses many existing components and was not designed for reusability, combining those components to create a new rocket proved more difficult than expected. The core stage, in particular, turned out to be surprisingly complex, as NASA struggled with the challenge of incorporating four engines. Once the first core stage was complete, it spent more than a year on a test stand at NASA’s Stennis Space Center in Mississippi, including two static-fire tests of its engines, before going to the Kennedy Space Center for launch preparations.
Those difficulties pushed back the first SLS launch by years, although not all the problems were within NASA’s control. Hurricanes damaged the Stennis test stand as well as the New Orleans facility where the core stage is built. The pandemic also slowed the work, before and after all the components arrived at the VAB for assembly. “In Florida in August and September [2021], it hit our area very hard,” said Mike Bolger, manager of the exploration ground systems program at NASA, describing the most recent wave of the pandemic at the October briefing.
Now, after years of delays, the first launch of the SLS is finally getting close. “Completing stacking [of the SLS] is a really important milestone. It shows that we’re in the home stretch,” said Mike Sarafin, NASA’s manager for the first SLS mission, called Artemis 1, at the same briefing.
After a series of tests inside the VAB, the completed vehicle will roll out to Launch Complex 39B. NASA will then conduct a practice countdown called a wet dress rehearsal—“wet” because the core stage will be loaded with liquid-hydrogen and liquid-oxygen propellants.
Controllers will go through the same steps as in an actual countdown, stopping just before the point where the RS-25 engines would normally ignite. “For us, on the ground, it’s a great chance to get the team and the ground systems wrung out and ready for launch,” Bolger said of the wet dress rehearsal.
This photograph shows a giant spherical storage tank with an adjacent stairway to the top and pipes leading to it that are close to the ground. This giant tank will help increase the capacity for storing liquid hydrogen at the Kennedy Space Center. Glenn Benson/NASA
After that test, the SLS will roll back to the VAB for final checks before returning to the pad for the actual launch. The earliest possible launch for Artemis 1 is 12 February 2022, but at the time of this writing, NASA officials said it was too soon to commit to a specific launch date.
“We won’t really be in a position to set a specific launch date until we have a successful wet dress [rehearsal],” Whitmeyer said. “We really want to see the results of that test, see how we’re doing, see if there’s anything we need to do, before we get ready to launch.”
To send the uncrewed Orion spacecraft to the moon on its desired trajectory, SLS will have to launch in one of a series of two-week launch windows, dictated by a variety of constraints. The first launch window runs through 27 February. A second opens on 12 March and runs through 27 March, followed by a third from 8 to 23 April. Sarafin said there’s a “rolling analysis cycle” to calculate specific launch opportunities each day.
A complicating factor here is the supply of propellants available. The core stage’s tanks store 2 million liters of liquid hydrogen and almost three-quarters of a million liters of liquid oxygen, putting a strain on the liquid hydrogen available at the Kennedy Space Center.
“This rocket is so big, and we need so much liquid hydrogen, that our current infrastructure at the Kennedy Space Center just does not support an every-day launch attempt,” Sarafin said. If a launch attempt is postponed after the core stage is fueled, Bolger explained, NASA would have to wait days to try again. That’s because a significant fraction of liquid hydrogen is lost to boil-off during each launch attempt, requiring storage tanks to be refilled before the next attempt. “We are currently upgrading our infrastructure,” he said, but improvements like larger liquid hydrogen storage tanks won’t be ready until the second SLS mission in 2023. There’s no pressure to launch on a specific day, Sarafin said. “We’re going to fly when the hardware’s ready to fly.”
SLS is not the only game in town when it comes to large rockets. In a factory located just outside the gates of the Kennedy Space Center, Blue Origin, the spaceflight company founded by Amazon’s Jeff Bezos, is working on its New Glenn rocket. While not as powerful as SLS, its ability to place up to 45 tonnes into orbit outclasses most other rockets in service today. Moreover, unlike SLS, the rocket’s first stage is reusable, designed to land on a ship.
New Glenn and SLS do have something in common: development delays. Blue Origin once projected the first launch of the rocket to be in 2020. By early 2021, though, that launch date had slipped to no earlier than the fourth quarter of 2022.
A successful SpaceX Starship launch vehicle, fully reusable and able to place 100 tonnes into orbit, could also make the SLS obsolete.
A key factor in that schedule is the development of Blue Origin’s BE-4 engine, seven of which will power New Glenn’s first stage. Testing that engine has taken longer than expected, affecting not only New Glenn but also United Launch Alliance’s new Vulcan Centaur rocket, which uses two BE-4 engines in its first stage. Vulcan’s first flight has slipped to early 2022, and New Glenn could see more delays as well.
Meanwhile halfway across the country, at the southern tip of Texas, SpaceX is moving ahead at full speed with its next-generation launch system, Starship. For two years, the company has been busy building, testing, flying—and often crashing—prototypes of the vehicle, culminating in a successful flight in May 2021 when the vehicle lifted off, flew to an altitude of 10 kilometers, and landed.
SpaceX is now preparing for orbital test flights, installing the Starship vehicle on top of a giant booster called, aptly, Super Heavy. A first test flight will see Super Heavy lift off from the Boca Chica, Texas, test site and place Starship in orbit. Starship will make less than one lap around the planet, though, reentering the atmosphere and splashing down in the Pacific about 100 kilometers from the Hawaiian island of Kauai.
When that launch will take place remains uncertain—despite some optimistic announcements. “If all goes well, Starship will be ready for its first orbital launch attempt next month, pending regulatory approval,” SpaceX CEO Elon Musk tweeted on 22 October 2021. But Musk surely must have known at the time that regulatory approval would take much longer.
SpaceX needs a launch license from the U.S. Federal Aviation Administration to perform that orbital launch, and that license, in turn, depends on an ongoing environmental review of Starship launches from Boca Chica. The FAA hasn’t set a schedule for completing that review. But the draft version was open for public comments through the beginning of November, and it’s likely to take the FAA months to review those comments and incorporate them into the final version of the report. That suggests that the initial orbital flight of Starship atop Super Heavy will also take place sometime in early 2022.
Starship could put NASA in a bind. The agency is funding a version of Starship to serve as a lunar lander for the Artemis program, transporting astronauts to and from the surface of the moon as soon as 2025. So NASA clearly wants Starship development to proceed apace. But a successful Starship launch vehicle, fully reusable and able to place 100 tonnes into orbit, could also make the SLS obsolete.
Of course, on the eve of the first SLS launch, NASA isn’t going to give up on the vehicle it’s worked so long and hard to develop. “SLS and Orion were purpose-designed to do this mission,” says Pam Melroy, NASA deputy administrator. “It’s designed to take a huge amount of cargo and people to deep space. Therefore, it’s not something we’re going to walk away from.”
Jeff Foust, a frequent contributor to IEEE Spectrum, is a senior staff writer with SpaceNews. He has a Ph.D. in planetary sciences from MIT and a B.S. in geophysics and planetary science from Caltech.
Design iteration times for topological insulators drop from days to minutes—superconductors, watch your back
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.
MIT researchers discovered hidden magnetic properties in multilayered electronic material by analyzing polarized neutrons using neural networks.
A new AI algorithm has been developed that offers to drastically trim back the time needed to iterate designs of a promising new material called the topological insulator.
The potential of topological insulators—which feature the strange property of being insulators on the inside but conductors on the outside—has transfixed electronics researchers for the past decade. One area of interest has been achieving electronics without dissipation, or loss to heat. For years the only material that seemed to offer electronics without resistivity were superconductors. However, superconductors lack a degree of robustness and were susceptible to the most minute of disturbances.
Topological insulators seemed to offer a reasonable alternative to the fragility of superconductors. However, to develop and perfect a topological insulator meant first understanding how a material’s magnetic and nonmagnetic layers interact—including the induced magnetism in the nonmagnetic layer—a phenomenon called the “magnetic proximity effect.” To detect this phenomenon researchers use a technique known as polarized neutron reflectometry (PNR) to analyze how magnetic structure varies as a function of depth in multilayered materials.
PNR, in other words, was a necessary element of developing topological insulators, but it’s also been a substantial slowdown in the process of exploring and iterating new possible materials. Both PNR’s inherent complexities and the vast amounts of data it produces have been a challenge.
“In traditional methods, people needed to spend time guessing at tens of parameters again and again. With this AI approach there is no need to guess—and it’s painless.”
—Mingda Li, MIT
However, now researchers at MIT have developed an artificial intelligence algorithm for sorting through all the PNR data to help researchers significantly reduce the data-analysis time.

“It has reduced the analysis from days to minutes without exaggeration,” said Mingda Li, professor at MIT and the principal researcher in this work. “In traditional methods, people needed to spend time guessing at tens of parameters again and again. With this AI approach there is no need to guess—and it’s painless.”
PNR starts by aiming two polarized neutron beams with opposing spins at a sample. Those beams are reflected off the sample and collected on a detector. If one of the neutrons comes in contact with a magnetic flux, such as those found inside a magnetic material, it will change its spin state, resulting in different signals measured from the spin-up and spin-down neutron beams. As a result, the proximity effect can be detected if a thin layer of a normally nonmagnetic material—placed immediately adjacent to a magnetic material—is shown to become magnetized: the magnetic proximity effect.
The PNR signal, as it’s first fed into the AI, is a complex signal that’s difficult to deconvolve. But in doubling the resolution of the signal, the AI is able, essentially, to amplify the proximity-effect component of the signal, thus making the data easier to interpret. In the group’s work, their algorithm could discern proximity-effect properties at length scales of 0.5 nanometer. (The typical spatial extent of the proximity effect, Li said, is on the order of one nanometer, so the AI is able to resolve to the size scales needed.)
The AI method succeeds over traditional algorithms, Li said, because it transforms the PNR data into a hidden “latent space”—a sort of simplified but still useful representation of compressed data—that makes analysis much easier.
To leverage this ability to transform data into latent space, each piece of PNR data is first labeled according to the particular parameters most relevant to the researchers. The algorithm then looks for nuanced links between different data points and amplifies them, in contrast to the conventional method of treating each data point independently.
The MIT researchers built their algorithm from PyTorch, the open-source machine-learning framework.
“We are not an AI group designing things like convolutional neural networks, but the package is powerful enough to be adopted in existing research facilities, like the [U.S.] National Institute of Standards and Technology,” said Li.
In addition to locating the proximity effect in PNR data, Li said, it can also be used for finding other nuanced spectral signals, such as SARS-CoV-2 virus in lipid bilayers (which is also measured by PNR). He also envisions using their algorithm to find materials that can host qubits for quantum computing. “Those are direct applications without need to modify much of [the] codes,” Li added.
In fact, quantum computing applications, Li said, are the most immediate applications for this AI beyond the PNR data mining.
“There has been some recent controversies in identifying whether some material systems may host qubits,” Li said. “This work will improve the resovability and help on that.”
It’s purportedly twice the speed of container ships—so can the venture sail?
Computer visualization of the Argo green LH2 hydrofoil cargo ship—a next-generation hydrofoil vessel that uses carbon-fiber composite wings and mast.
With a hundred years of history backing them, hydrofoils are known for their high speeds. Swiftness is achieved by using aircraft-like wings beneath the craft to lift the hull out of the water and “fly” above the surface to reduce drag. Their popularity peaked in the 1970s only to decline thereafter due to reasons like stability challenges, materials issues, and high production and maintenance costs.
But now, Boundary Layer Technologies (BLT), a four-year-old marine technology startup based in Alameda, Calif., aims to use the technological advances of the past 50 years to create Argo, a liquid hydrogen (LH2) hydrofoil cargo vessel, to vie with container ship and airfreight transport—the latter business alone being valued at over US $6 trillion.
“Every aspect of the technology that goes into foiling ships has advanced since the ’70s,” says Ed Kearney, founder and CEO of BLT. In particular, the use of carbon-fiber composite for the wings and mast, in place of the previously used stainless steel “has solved the structural performance of the wings. They are now more slender, create less drag, and so significantly decrease fuel use.”
Traditionally, hydrofoils “have been small because of the higher energy demands of larger boats (on lift-off),” says Zhaohui Qin, who teaches computational fluid dynamics at Cedarville University, in Ohio, and who advised the college’s winning design team in the 2019 Mandles Prize for Hydrofoil Excellence. However, he agrees the reduction in weight with the development of composite materials makes larger vessels like Argo possible.
Other technology advances include computing power and computational fluid-dynamics simulation software that enables engineers to design wings using numerous iterations in fluid simulations, compared to using towing tanks, which makes Argo more economical and quicker to design.
To avoid hitting floating objects, Argo will employ X-band radar. And forward-scanning sonar will be used to detect submerged objects and mammals at ranges up to 1,500 meters, which will give pilots up to about 75 seconds to avoid submerged obstacles, says Kearney.
Argo will also have around 1.6 megawatt-hours of lithium-ion batteries on board primarily to boost the power needed to raise the hull up to 5 meters above the surface—including the payload of 200 tons, 70 percent more than a Boeing 747-400 freighter. It is designed to have a range of almost 2,800 kilometers, and a cruising speed of 40 knots—twice as fast as container ships, according to BLT.
Although popularized decades ago, hydrofoil technologies have advanced by leaps and bounds in recent years, due to both advanced materials and smart CAD simulation environments, says Boundary Layer Technologies CEO Ed Kearney. Boundary Layer Technologies
But Stephen Turnock, professor of maritime fluid dynamics and head of the Department of Civil, Maritime and Environmental Engineering at the University of Southampton, England, queries some of BLT’s claims. “In principle, hydrofoils can go faster [than container ships] for the same installed power. But doubling the speed sounds like a marketing line. For many ship voyages, local speed limits restrict the gains that can be made during the high-speed part of the voyage.”
Qin echoes this reservation, questioning whether Argo can achieve such “speed advantages and still be economically profitable.”
Argo will carry the liquid hydrogen in 26,000-kilogram, 370-cubic-meter LH2 tanks housed in the vessel’s two hulls. A vaporizer supplies the conditioned gaseous H2 to a 10-megawatt fuel-cell stack. DC power from the stack is converted to AC and fed to motor inverters to drive the propulsion system. The propulsion system comprises four 2.5-MW motors that drive contrarotating propellers via Z-drive gearing, which enables rapid changes in thrust direction.

Kearney points out that industry has been using liquid and gaseous hydrogen for over 100 years, and consequently, safety protocols are very well understood. So he doesn’t envisage any special problems when it comes to using LH2.
Turnock agrees that hydrogen can be operated safely, which is why shipping authorities are looking into developing protocols needed to operate vessels using hydrogen and fuel cells. But he notes that the fast foiling of hydrofoils may create additional hazards, which is why they must also ensure the H2 and fuel-cell systems are sufficiently well protected in the event of a collision.
Argo is slated to launch in 2024. “We will likely have to rely on a mix of blue and green hydrogen from countries like China, Japan, and [South] Korea to service our initial intra-Asia trade routes,” says Kearney. But by early 2025, he notes Australia is due to supply Asia with 118,000 tonnes of green hydrogen annually. “And we’re already talking with producers to secure long-term supply contracts.”
Currently, the Argo team is specifying the design requirements for the major systems and modeling their performance. But Kearney says they have built, tested, and demonstrated 60 percent of the technology in prototype vessels. According to Kearney, in 2019, they completed a prototype called the P3— the first hydrofoiling container ship. It was built in 10 weeks for a cost of $150,000, as proof of concept.
The company has secured financial backing from Y Combinator, Lower Carbon Capital, and other, unnamed, backers. In addition, it has received a $180 million letter of intent from Flexport, a digital freight forwarder interested in shipping components for electronics makers in Asia, where BLT intends to begin freight services.
Meanwhile, the company plans to launch an electric hydrofoil ferry, Electra, in Q1 2024. It is designed to carry 150 passengers and cruise at 40 knots with a range of 185 km, its power coming from a 9,000 kWh lithium-ion battery system.
“Electra has more than an 80 percent technology overlap with Argo,” says Kearney. “By reducing drag by a factor of two, its power requirements are halved, which increases its speed and range.”
By launching the smaller Electra ahead of Argo, Kearney sees it bringing in early revenues, as BLT works with partners to develop its freight service.
“During the next 18 months, we will build and test full-scale Argo major subsystems,” says Kearney. Construction is targeted to begin in Q3 2023, and operations to start in Q3 2024.
The business plan calls for Argo to provide door-to-door transit times just 15 to 24 hours longer than air freight, but at 50 percent of the cost. Given the vessel’s small size—33 meters in length—Kearney says Argo will be able to bypass congested ports and unload and reload in only 2 hours, compared to three days for larger container ships.
That’s if all goes according to plan, of course. BLT is still working to reach the functional design stage, so there is much to do and no doubt challenges to overcome before even a full-scale prototype is ready to test.
But as Turnock points out, the world is today moving both toward decarbonization and away from the luxury of flying—both of which open up a niche for new emission-free, non-aircraft-based competitors.
Qin agrees, saying Argo has the potential to compete in relatively short-distant transport markets, if its claimed efficiency and low pricing is realized.
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