March 30, 2023

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Years after the shuttle, NASA rediscovered the dangers of liquid hydrogen

Years after the shuttle, NASA rediscovered the dangers of liquid hydrogen

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

Kennedy Space Center, Florida.— The US space agency on Saturday sought to launch a largely paved rocket from the space shuttle, which was designed and built more than four decades ago.

Since the Space Shuttle has often been delayed due to technical issues, it is surprising that the first launch of NASA’s Space Launch System rocket was removed a few hours before the launch window opened. The showstopper was an 8-inch line carrying liquid hydrogen to the rocket. This resulted in a continuous leak in the intake, known as a quick disconnect, leading into the vehicle.

Valiantly, the launch team at the Kennedy Space Center tried three different times to stop the leak, to no avail. Finally at 11:17 a.m. ET, after hours of the refueling schedule, launch manager Charlie Blackwell-Thompson called for a halt.

What comes next depends on what engineers and technicians find on Monday when they inspect the car at the launch pad. If the launch team decides they can replace the onboard quick disconnect device, it may be an option to perform a partial fuel test to determine the integrity of the repair. This may allow NASA to keep the vehicle on the platform before the next launch. Alternatively, engineers may decide that repairs are best done inside the vehicle assembly building, and return the missile back inside.

Due to the orbital dynamics of the Artemis I mission to transport an unmanned Orion spacecraft to the Moon, NASA will then have the opportunity to launch from September 19 to October 4. Then obtain a waiver from the US Space Force, which operates the launch range along the Florida coast.

The dispute revolves around the flight termination system, which operates independently of the missile, with batteries rated for 25 days. NASA will need to extend this battery rating to about 40 days. The space agency is expected to have these discussions with field officials soon.

If the rocket is returned to the Vehicle Assembly Building, which will be a necessary service to the flight termination system or do more than quick work on the launch pad, NASA has another opportunity to launch Artemis I from October 17 to October 31.

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very small item

The Space Shuttle was a very complex vehicle, blending the use of solid rocket boosters – which are something like very powerful fireworks – along with exquisitely built main engines that combusted liquid hydrogen fuel and liquid oxygen to act as an oxidizer.

Over its life, due to this complexity, the shuttle was cleaned on average about once per launch attempt. Some shuttle flights were washed up to five times before finally taking off. For the launch controllers, the complex refueling of the space shuttle was not very easy to manage, and hydrogen was often the culprit.

Hydrogen is the most abundant element in the universe, but it is also the lightest. it takes 600 sextillion Hydrogen atoms have a mass of one gram. Because it is so small, hydrogen can squeeze through the tiniest of gaps. This is not a huge problem at ambient temperatures and pressures, but at extremely cold temperatures and high pressures, hydrogen easily leaks out of any available opening.

To keep the rocket fuel tanks at the front, the fuel lines leading from the ground systems must remain connected to the booster until the moment of launch. At the last second, the “quick disconnect” at the end of these lines separates from the rocket. The difficulty is that, in order for this equipment to be secure in separation from the rocket, it cannot be attached together tightly enough to completely block the passage of hydrogen atoms—it is extremely difficult to seal these connections under high pressure and low temperatures.

Therefore, NASA tolerates a small amount of hydrogen leakage. However, anything above 4 percent hydrogen concentration in the purge zone near rapid separation is considered a flammability hazard. “we “They were seeing two or three times more than that,” said Mike Sarafin, NASA’s Artemis I mission manager. It was obvious that we wouldn’t be able to make our way through it. Every time we see a leak, it quickly crosses the flammability limits.”

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The launch controllers turned off the hydrogen flow into the car twice, hoping the quick disconnect would warm up a bit. They hoped that when the slowly flowing hydrogen aboard the rocket was restarted, the rapid separation would find a tighter fit with the booster. you did not. Again they tried to apply a great deal of pressure to bring back the quick separation seat.

NASA officials are still assessing the cause of the leak, but they believe it may have been due to a faulty valve opening. This happened during the cooling process of the rocket before loading liquid hydrogen fuel. Amidst a series of about a dozen commands being sent to the missile, a command was sent to a faulty valve to open it. This was corrected within 3 or 4 seconds, Sarafin said. However, during this time, the hydrogen line that would develop a rapid detachment problem was briefly hyperpressurised.

Referral to experts

So why would NASA use liquid hydrogen as fuel for its rockets, if it’s so hard to handle, and it’s easier to deal with alternatives like methane or kerosene? One reason is that hydrogen is a very efficient fuel, which means it provides “more gas mileage” when used in rocket engines. However, the real answer is that Congress mandated NASA to continue using the Space Shuttle’s main engines as part of the SLS rocket program.

In 2010, when Congress wrote NASA authorization bill Leading to the creation of the Space Launch System, it directed the agency to “leverage on existing contracts, investments, investments, manpower, industrial base, and capabilities from the Space Shuttle and Orion and Ares 1 projects, including … existing propulsion systems in the United States, including liquid-fuel engines, and external tank or tank related capabilities, and solid rocket engines.”

During a press conference Saturday, Ars asked NASA Administrator Bill Nelson if it was the right decision for NASA to continue working with hydrogen after the agency’s experience with the space shuttle. In 2010, Nelson was a US senator from Florida, and the leader of the space authorization bill alongside US Senator Kay Bailey Hutchison of Texas. “We’re back to the experts,” Nelson said.

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By this Nelson meant that the Senate worked alongside some officials at NASA, and within the industry, to design the SLS rocket. Those industry officials, who would go on to win lucrative contracts from NASA for their work on the shuttle-related hardware, were very happy to support the new rocket’s design.

Among the opponents of the idea was Laurie Garver, who served as NASA’s deputy administrator at the time. She said the decision to use Space Shuttle components for the agency’s next-generation rocket sounded like a terrible idea, given the challenges of working with hydrogen that have emerged over the past three decades.

“They took difficult, expensive software that couldn’t fly very much, and put them together differently, and they said now, all of a sudden, it’s going to be cheap and easy,” she said. “Yes, we’ve moved them before, but they’ve proven to be both problematic and challenging. That’s one of the things that baffled my mind. And what about that would change? I attribute that to this kind of groupthink, contractors and ice cream cone licking.”

Now, NASA is taking on the challenge of managing these difficult devices with more inspections and tests after so much already. The rocket’s core stage, made by Boeing, shipped from its Louisiana plant more than two and a half years ago. It underwent nearly a year of testing in Mississippi before arriving at the Kennedy Space Center in April 2021. Since then, NASA and its contractors have been working to fully assemble the rocket and test it on the launch pad.

Effectively, Saturday’s “launch” attempt was the sixth time NASA has attempted to refuel the first and second stages of the rocket, then delve deeper into the countdown. So far, it hasn’t passed any of these refueling tests, known as wet-cloth proofs. On Saturday, the base’s massive liquid hydrogen tank, with a capacity of more than 500,000 gallons, was only 11 percent full when the scrub was called.

Maybe the seventh time is magic.