NASA's Space Launch System rocket launches at LC-39B on September 1, 2022.

Years after space shuttle, NASA rediscovers dangers of liquid hydrogen

enlarge / NASA’s Space Launch System rocket launches at LC-39B on September 1, 2022.

Kennedy Space Center, Florida— On Saturday, NASA attempted to launch a rocket largely cobbled together from the space shuttle, which itself was designed and built more than four decades ago.

With the space shuttle often delayed by technical issues, it’s no surprise that the first launch of NASA’s Space Launch System rocket was scrubbed hours before the launch window opened. The showstopper is an 8-inch-diameter pipeline that carries liquid hydrogen into the rocket. It had a persistent leak at the entrance, called a quick disconnect, that led to the vehicle.

The Kennedy Space Center launch team made valiant attempts to stop the leak 3 different times, to no avail. Finally at 11:17 a.m. ET, hours behind their schedule to refuel the rocket, launch director Charlie Blackwell-Thompson called it off.

What happens next depends on what engineers and technicians find when they inspect the vehicle at the launch pad on Monday. If the launch team decides that the quick-disconnect hardware on the launch pad can be replaced, there is an option to perform a partial refueling test to determine the integrity of the repair. This could allow NASA to keep the vehicle on the launch pad until the next launch. Alternatively, engineers may decide that repairs are best done in the vehicle assembly building and roll the rocket back inside.

Thanks to the orbital dynamics of the Artemis 1 mission, sending the unmanned Orion spacecraft to the moon, NASA will next have the opportunity to launch between September 19 and October 4. Making the window, however, required securing the rocket to the launch pad and then getting a waiver from the U.S. Space Force, which operates the launch site off the coast of Florida.

The problem is the flight termination system, which is powered independently of the rocket and has a battery life of 25 days. NASA needs to extend the battery life rating to about 40 days. The space agency is expected to have these discussions with range officials soon.

If the rocket rolls back to the Vehicle Assembly Building, which will be necessary to service the flight termination system or perform more cursory work on the launch pad, then NASA has another Artemis I from Oct. 17 to Oct. 31. launch opportunity.

a tiny element

The Space Shuttle is an extremely complex vehicle that mixes the use of solid rocket boosters—similar to very, very powerful firecrackers—and an ingenious main engine powered by the combustion of liquid hydrogen propellant and liquid oxygen, as an oxidizer.

Due to this complexity, the shuttle will scrub almost once per launch attempt, on average, over its lifetime. Some shuttles were scrubbed as many as five times before finally taking off. For launch controllers, managing the shuttle’s complex refueling process has never really been much easier, and hydrogen is often the culprit.

Hydrogen is the most abundant element in the universe, but also the lightest. need 600 600 million Hydrogen atoms reach a mass of one gram. Because it’s so small, hydrogen can squeeze through the smallest of gaps. At ambient temperature and pressure, this isn’t much of a problem, but at ultra-low temperatures and high pressures, hydrogen can easily seep out of any available opening.

To keep the rocket’s fuel tanks full, the propellant lines from the ground system must remain connected to the booster until the moment of launch. At the last second, “quick disconnects” at the ends of these lines separate from the rocket. The difficulty is that, in order to be failsafe when disconnected from the rocket, the device cannot be bolted tight enough to completely block the passage of hydrogen atoms — sealing those connections at high pressure and low temperatures is extremely difficult.

Therefore, NASA can tolerate small hydrogen leaks. However, in the purge area near the quick disconnect, any hydrogen concentration above 4% is considered a flammability hazard. “us “We’re seeing two to three times more than that,” said Mike Sarafin, NASA’s Artemis 1 mission manager. “Obviously, we can’t get through it. Every time we see a leak, it’s very Our flammability limit is almost exceeded.”

Twice, the launch controller stopped the flow of hydrogen into the vehicle, hoping the quick disconnect would warm up a little. They hope the quick disconnects will work more closely with the boosters when they restart the slow-flowing, cryogenic hydrogen on the rocket. It didn’t. Another time, they tried to put a lot of pressure to reinstall the quick disconnect.

NASA officials are still evaluating the cause of the leak, but they believe it may have been due to the wrong valve being opened. This happens during the cooling of the rocket before loading the liquid hydrogen propellant. In a sequence of about a dozen commands sent to the rocket, one was sent to the wrong valve to open. This is corrected within 3 or 4 seconds, Sarafin said. During this period, however, the problematic quick-disconnect hydrogen line was briefly overpressurized.

follow the experts

So why does NASA use liquid hydrogen as fuel for its rockets, if liquid hydrogen is so difficult to use and there are easier-to-handle alternatives like methane or kerosene? One reason is that hydrogen is a very efficient fuel, which means it provides better “fuel consumption” when used in rocket engines. The real answer, however, is Congress requiring NASA to continue using the space shuttle main engine as part of the SLS rocket program.

In 2010, when Congress wrote the authorization bill for NASA that led to the creation of the Space Launch System, it directed the agency to “leverage existing contracts, investments, labor, industrial base, and capabilities of the Space Shuttle, Orion, and Ares 1 programs, including… …existing U.S. propulsion systems, including liquid-fuel engines, external fuel tanks or tank-related capabilities, and solid rocket motors.”

During a news conference Saturday, Ars asked NASA Administrator Bill Nelson if it was the right decision for NASA to continue using hydrogen after gaining experience with the space shuttle. In 2010, Nielsen was a U.S. senator from Florida and, along with U.S. Senator Kay Bailey Hutchison of Texas, was the leader of the space authorization bill. “We listen to the experts,” Nelson said.

What Nelson means is that the Senate designed the SLS rocket with some officials from NASA and industry. These industry officials will continue to receive lucrative contracts from NASA, work on space shuttle-related hardware, and are more than happy to support new rocket designs.

One of the opponents of the idea was Lori Garver, who was NASA’s deputy administrator at the time. Given the challenges of using hydrogen over the past 30 years, the agency’s decision to use space shuttle components for its next-generation rockets seemed like a bad idea, she said.

“They take finicky, expensive procedures that can’t be flown very often, stack them in different ways, and then all of a sudden, it’s going to be cheap and easy,” she said. “Yeah, we’ve driven them before, but they’ve proven to be problematic and challenging. That’s one of the things that blows my mind. How does it change? I attribute it to this groupthink, contracting Traders and self-licking ice cream cones.”

Now, NASA faces the challenge of managing this finicky hardware with more inspection and testing. The rocket’s core stage is built by Boeing and shipped from its factory in Louisiana two and a half years ago. It spent nearly a year in Mississippi testing before arriving at Kennedy Space Center in April 2021. Since then, NASA and its contractors have been assembling the complete rocket and testing it on the launch pad.

In fact, Saturday’s “launch” attempt was NASA’s sixth attempt to fully fuel the rocket’s first and second stages before the countdown began. To date, it has not successfully passed any of these refueling tests, the wet dress rehearsal. On Saturday, the core-level large liquid hydrogen tank had a capacity of more than 500,000 gallons, but was only 11 percent full when the scrub was called.

Maybe the seventh time will be a charm.

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