Why Hydrogen Leaks Continue to Be a Major Headache for NASA Launches

NASA’s Space Launch System is powered by a mix of liquid hydrogen and liquid oxygen. Together, these parts present for a compact and intensely highly effective rocket propellant, however these identical attributes are additionally what make this gasoline a legal responsibility.

The second launch try of SLS needed to be referred to as off on Saturday, September 3, after engineers didn’t resolve a hydrogen leak in a fast disconnect—an 8-inch inlet that connects the liquid hydrogen gasoline line to the rocket’s core stage. As a results of the setback, SLS in all probability gained’t launch till October on the earliest. The Artemis 1 mission, during which an uncrewed Orion spacecraft will journey to the Moon and again, should wait.

Ground groups have been in a position to repair a hydrogen leak through the first failed launch try on Monday, August 29, however the launch was finally referred to as off after a defective sensor erroneously indicated that an engine hadn’t reached the required ultra-cold temperature. The leak on Saturday proved to be far more troublesome to include, with engineers making an attempt three fixes, none of which labored. “This was not a manageable leak,” Mike Sarafin, Artemis mission supervisor, advised reporters after the scrub.

NASA continues to be evaluating its subsequent steps, however the rocket should return to the Vehicle Assembly Building to endure a mandated security verify associated to its flight termination system. The rocket could require some {hardware} fixes on account of an inadvertent command that briefly raised the stress throughout the system. The unintended over-pressurization could have contributed to the leaky seal, and it’s one thing engineers are at the moment evaluating as a risk.

Inheriting the hydrogen downside

Hydrogen leaks are nothing new for NASA. Scrubs of Space Shuttle launches occurred with upsetting regularity and have been usually the results of hydrogen leaks. One of the extra notorious episodes was “the summer of hydrogen,” when floor groups spent greater than six months making an attempt to find an elusive hydrogen leak that grounded the Shuttle fleet in 1990. SLS is closely modeled after the Space Shuttle, together with using liquid hydrogen propellant, so hydrogen-related scrubs may actually have been predicted. But SLS is what it’s, and NASA has little selection however to handle this limitation of its mega Moon rocket.

Jordan Bimm, an area historian on the University of Chicago, says NASA continues to make use of liquid hydrogen for political slightly than technical causes.

“Since the creation of NASA in 1958, the agency has used contractors located around the U.S. as a way to maintain broad political support and funding for space exploration in Congress,” Bimm advised me. “The first system to use liquid hydrogen was the Centaur rocket developed in the 1950s and 1960s. In 2010, the U.S. Congress, in their authorization act funding NASA, mandated that the Agency use existing technologies from the Shuttle in their next-generation launch system.” To which he added: “This was a political decision meant to maintain contractor jobs in key political districts and from that funding and support in Congress for NASA.”

This growth meant that the RS-25 engine from the retiring Space Shuttle, together with its reliance on a liquid hydrogen/liquid oxygen combination, must be carried over to SLS. In whole, NASA managed to gather 16 engines from the retired Shuttles, of which 4 are at the moment affixed to the SLS rocket standing on the launch pad at Kennedy Space Center in Florida.

This scenario, stated Bimm, is a reminder of the catchphrase from the 1983 movie The Right Stuff: “No bucks, no Buck Rogers.” NASA, he stated, “must often prioritize shoring-up political support from Congress to maintain its exploration program.” The ongoing use of RS-25 engines “is another example of how something as mundane as fuel choice can be political and how often the most straightforward and desirable solutions are not politically viable for a large national agency created in the Cold War era of ‘Big Science’,” stated Bimm.

Instead of choosing propellants like methane or kerosene, NASA selected to make use of a mix of liquid hydrogen and liquid oxygen to energy its heavy-lift rocket. By comparability, SpaceX’s upcoming Starship makes use of liquid methane, with liquid oxygen because the oxidizer. “With their sights set on Mars, SpaceX selected liquid methane in the hopes of being able to extract this element [when] on Mars as a form of cost-saving resource utilization,” Bimm defined. The U.S. area company, perpetually cash-strapped and having to please politicians, was working underneath a unique set of rules when designing SLS.

“Based on current information and analysis, the [proposed SLS design] represents the lowest near-term costs, soonest available, and the least overall risk path to the development of the next, domestic heavy lift launch vehicle,” wrote NASA in a 2011 preliminary project report. “Selecting this SLS architecture would mean that a new liquid engine in the near term would not need to be developed, thus shortening the time to first flight as well as likely minimizing the overall…cost of the SLS.”

The irony is that SLS, which was alleged to fly in 2017, has but to launch, and its whole growth prices, together with the Orion crew capsule, have now exceeded $50 billion. That excludes the estimated $4.1 billion price pegged for every launch of SLS. And by inheriting Space Shuttle parts, NASA has additionally inherited the hydrogen downside.

A helpful however pesky molecule

Hydrogen is extraordinarily helpful as a rocket gasoline. It’s available, clear, light-weight, and, when mixed with liquid oxygen, burns with excessive depth. “In combination with an oxidizer such as liquid oxygen, liquid hydrogen yields the highest specific impulse, or efficiency in relation to the amount of propellant consumed, of any known rocket propellant,” according to NASA. When chilled to -423 levels Fahrenheit (-253 levels Celsius), hydrogen might be crammed right into a rocket, providing an amazing quantity of gasoline for the buck. “The advantages of liquid hydrogen as a fuel is its efficiency at storing the energy you want to release to propel the rocket, as well as its low weight, which is always a consideration in spaceflight,” stated Bimm.

NASA’s Apollo-era Saturn rocket second stage used liquid hydrogen, as did the Shuttle’s three primary engines. Hydrogen is often used for second levels (Europe’s heavy-lift Ariane 5 rocket is an efficient instance), and because the liquid gasoline wanted for maneuvering spacecraft in orbit. Rockets that at the moment use liquid hydrogen embrace Atlas’s Centaur and Boeing’s Delta III and IV, whereas Blue Origin’s BE-3 and BE-7 engines additionally depend on hydrogen.

“The disadvantages of hydrogen are that it is very difficult to move around and control due to the small molecular size of hydrogen which leads to leaks and the need to keep it in a liquid state which requires cooling to extremely low temperatures,” stated Bimm. What’s extra, hydrogen is extremely unstable when in a liquid state, and it may well burn in giant portions. As the lightest identified ingredient, it’s additionally very leaky. NASA explains the numerous challenges of utilizing liquid hydrogen as gasoline:

To maintain it from evaporating or boiling off, rockets fuelled with liquid hydrogen have to be fastidiously insulated from all sources of warmth, resembling rocket engine exhaust and air friction throughout flight by way of the ambiance. Once the automobile reaches area, it have to be shielded from the radiant warmth of the Sun. When liquid hydrogen absorbs warmth, it expands quickly; thus, venting is important to stop the tank from exploding. Metals uncovered to the acute chilly of liquid hydrogen turn into brittle. Moreover, liquid hydrogen can leak by way of minute pores in welded seams.

Despite these challenges, NASA opted for liquid hydrogen when designing SLS, and now it’s paying the worth.

New rocket, standard issues

When tanking SLS, the sudden inflow of cryogenic hydrogen causes vital adjustments to the rocket’s bodily construction. The 130-foot-tall (40-meter-tall) hydrogen tank shrinks about 6 inches (152 mm) in size and about 1 inch (25.4 mm) in diameter when stuffed with the ultra-cold liquid, according to NASA. Components hooked up to the tank, resembling ducts, vent strains, and brackets, should compensate for this sudden contraction. To obtain this, NASA makes use of connectors with accordion-like bellows, slotted joints, telescoping sections, and ball joint hinges.

But hydrogen—the smallest molecule within the universe—usually finds its approach by way of even the tiniest of openings. The gasoline strains are notably problematic, as they can’t be hard-bolted to the rocket. As their title suggests, the fast disconnects, whereas offering a decent seal, are designed to interrupt free from the rocket throughout launch. This seal should forestall leakage underneath excessive pressures and ultra-cold temperatures, nevertheless it additionally must let go because the rocket takes flight. On Saturday, a leak within the neighborhood of the fast disconnect reached concentrations nicely past the 4% constraint, exceeding NASA’s flammability limits. Unable to resolve the leak, NASA referred to as the scrub.

That NASA has but to completely gasoline the primary and second levels and get deep into the countdown is a real trigger for concern. The area company has handled hydrogen leaks earlier than, so hopefully its engineers will as soon as once more devise an answer to maneuver the venture ahead.

Still, it’s a irritating begin to the Artemis period. NASA wants SLS because it seeks a everlasting and sustainable return to the lunar atmosphere, and because it eyes a future human mission to Mars. NASA goes to must make SLS work, and it might need to take action one aggravating scrub at a time.