Years after shuttle, NASA rediscovers the perils of liquid hydrogen

America's space agency on Saturday sought to launch a rocket largely cobbled together from the space shuttle which itself was designed and built more than four decades ago

It comes as no surprise that the launch of NASA's Space Launch System rocket was scrubbed a few hours before it was supposed to go off. There was a line that carried liquid hydrogen into the rocket. A quick-disconnect is a persistent leak at the inlet.

The launch team at Kennedy Space Center tried a number of times to stop the leak. The launch director called a halt at 11:17 am due to hours behind on their timelines.

Engineers and technicians are going to inspect the vehicle at the launch pad on Monday. A partial fueling test may be an option if the launch team decides to replace the quick-disconnect hardware. NASA may be able to keep the vehicle on the pad in the future. The engineers could decide to perform the repairs inside the Vehicle Assembly Building.

NASA will be able to launch from September 19 to October 4 because of the dynamics of the Artemis I mission. The US Space Force, which operates the launch range along the Florida coast, would have to grant a waivers to make that window happen.

The flight terminated system is powered by batteries that can last 25 days. The battery rating needs to be extended by about 40 days. The space agency is going to have some talks with range officials.

NASA has an Artemis I launch opportunity from October 17 to October 31 if the rocket is rolled back to the Vehicle Assembly Building.

A tiny, tiny element

The space shuttle was an extremely complex vehicle, mingling the use of solid-rocket boosters, which are something akin to very, very powerful firecrackers, along with exquisitely built main engines powered by the combustion of liquid hydrogen propellant and liquid Oxygen to serve as an oxidizer.

The shuttle scrubbed almost every launch attempt over its lifetime. The shuttles scrubbed as many as five times. It wasn't easy for launch controllers to manage the space shuttle's complex fueling process.

The lightest element in the universe is hydrogen. The mass of a single gram requires 600 sextillion hydrogen atoms to be reached. Hydrogen can squeeze through the smallest gaps because it is so small. It's not a big problem at ambient temperatures and pressures, but it's a big problem at high pressures.

To keep a rocket's fuel tanks topped off, propellant lines leading from ground must remain attached to the booster until the very moment of launch. The lines break away from the rocket in the last second. It is difficult to seal these connections under high pressure and low temperatures in order to be fail-safes in detaching from the rocket.

NASA has a tolerance for small amounts of hydrogen leaking. Anything higher than a 4% concentration of hydrogen in the purge area is considered a fire hazard. NASA's Artemis I Mission Manager said that the hydrogen leak was two or three times larger. We weren't going to be able to work our way through it. It exceeded our flammability limits when we saw a leak.

In the past, launch controllers stopped the flow of hydrogen into the vehicle in order to warm it up. They wanted the quick-disconnect to fit better with the booster when they started again. The thing didn't. They applied a lot of pressure to re-seat the quick connect.

NASA believes that the leak may have been caused by an open valve. During the chilling down of the rocket, this happened. A command was sent to a wrong valve during a sequence of commands being sent to the rocket. The problem was fixed within 3 or 4 seconds. There was a brief over-pressurization of the hydrogen line.

Deferring to the experts

Why does NASA use liquid hydrogen as a fuel for its rockets if it is so difficult to work with and there are better alternatives? Hydrogen provides better "gas mileage" when used in rocket engines because it is a very efficient fuel. The answer is that Congress mandated that NASA continue to use space shuttle main engines.

Congress directed NASA in 2010 to use existing contracts, investments, workforce, industrial base, and capabilities from the Space Shuttle and Ares 1 projects.

Ars asked NASA Administrator Bill Nelson if it was the right decision to continue working with hydrogen after the space shuttle. Nelson was one of the leaders of the space authorization bill.

Nelson meant that the Senate was involved in the design of the SLS rocket. The industry officials, who would continue to win lucrative contracts from NASA for their work on shuttle related hardware, were happy to support the new rocket design.

Garver was NASA's deputy administrator at the time. She said the decision to use space shuttle components for the agency's next generation rocket seemed like a terrible idea, given the challenges of working with hydrogen.

She told Ars in August that they took programs that couldn't fly very often and stacked them together differently to make it easier to use. We've flown them before but they've proven to be problematic. This is something that made me think. It was going to change. The contractors and the ice cream cone are to blame.

NASA is facing the challenge of managing this hardware through more tests and inspections. The core stage of the rocket was manufactured by Boeing in Louisiana. It was tested in Mississippi before it arrived at Kennedy Space Center. The complete rocket has been assembled and tested on the launch pad.

Saturday's launch attempt was the sixth time NASA has tried to completely fuel the first and second stages of the rocket. It has failed all of the wet dress rehearsals. When the scrub was called, the liquid hydrogen tank was only 11 percent full.

It might be the seventh time that it will work out.