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

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

KENNEDY SPACE CENTER, Fla.—The U.S. space agency on Saturday sought to launch a largely DIY rocket from the space shuttle, which itself was designed and built more than a thousand years ago. four decades.

As the space shuttle has often been delayed due to technical issues, it's no surprise that the first launch of NASA's Space Launch System rocket was canceled hours before its launch window opened. launch. The highlight of the show was an 8-inch-diameter line carrying liquid hydrogen into the rocket. It caused a persistent leak at the inlet, known as a quick disconnect, leading aboard the vehicle.

Valiantly, the Kennedy Space Center launch team tried three times to stop the leak, to no avail. Finally, at 11:17 a.m. ET, hours behind their schedule to fuel the rocket, launch director Charlie Blackwell-Thompson called a halt.

What happens next depends on what engineers and technicians find Monday when they inspect the vehicle on the launch pad. If the release team decides they can replace the quick disconnect hardware at the pad, it may be possible to perform a partial refueling test to determine the integrity of the patch. 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 roll the rocket inside.

Due to the orbital dynamics of the Artemis I mission to fly an uncrewed Orion spacecraft to the Moon, NASA will then have the opportunity to launch from September 19 to October 4. However, creating this window would require attaching the rocket to the pad and then obtaining a waiver from the US Space Force, which operates the launch area along the Florida coast.

The problem is the flight termination system, which is powered independently of the rocket, with batteries that last for 25 days. NASA is expected to extend this battery capacity to around 40 days. The space agency should soon have these discussions with those responsible for the range.

If the rocket is brought back to the vehicle assembly building, which would be required to service the flight termination system or perform more than cursory launch pad work, NASA has another launch opportunity. 'Artemis I from October 17 to October 31.

A very small element

The Space Shuttle was an extremely complex vehicle, mixing the use of solid rocket boosters - which are akin to very, very powerful firecrackers - with exquisitely constructed main engines powered by the combustion of liquid hydrogen propellant and liquid oxygen to serve as an oxidant.

During its lifetime, due to this complexity, the Shuttle has rubbed up on average nearly once with every launch attempt. Some shuttle flights have been cleaned up to five times before finally taking off. For launch controllers, it has never really been easier to manage the complex space shuttle refueling process, 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 of hydrogen atoms to reach the mass of a single gram. Because it's so small, hydrogen can squeeze through the smallest of spaces. This is not such a serious problem at ambient temperatures and pressures, but at elevated temperatures and pressures, hydrogen easily escapes from any available opening.

To keep a rocket's fuel tanks filled, propellant lines from ground systems must remain attached to the propellant until the moment of launch. In the last second, the "quick disconnects" at the end of these lines detach from the rocket. The difficulty is that, to be safe from failure when disconnecting the rocket, this equipment cannot be bolted down enough to entirely prevent the passage of hydrogen atoms - it is extremely difficult to seal these connections under high pressure and low temperature. .

So NASA has a tolerance for a small amount of hydrogen leakage. However, anything above a 4% hydrogen concentration in the purge area near the quick disconnect is considered a flammability hazard. "We've seen two or three times as many," Mike Sarafin, NASA's Artemis I mission manager, said of Saturday's hydrogen leak. "It was pretty clear that we weren't going to be able to get out of this. Every time we saw a...