The Broom Method
A NASA worker demonstrating the broom method of detecting a hydrogen flame, which are invisible during the day. (Source: NASA)
In order to fuel its rockets, NASA scientists must take two of the most basic elements, hydrogen and oxygen, and cool them down hundreds of degrees into their liquid states. In this more efficient form, a rocket’s tank volume can be maximized, providing the needed fuel to achieve lift. This process is a potentially dangerous one, as hydrogen is highly combustible. If at any point during storage, fueling, or flight the liquid form evaporates back into gas, a leak could mean a massive explosion.
NASA has had a long history of contending with this issue. Hydrogen leaks were a persistent thorn in the side of the Space Shuttle program, grounding the entire fleet for six months while engineers searched for an elusive leak during the “Summer of Hydrogen”. Because of its efficiency as a fuel source, hydrogen continues to be used by many space agencies, as opposed to other alternatives.
The Endeavour orbiter returning from space after STS-118. This mission was the first to deploy hydrogen tape, which luckily caught a leak before takeoff. (Source: NASA)
In spite of the dangers of hydrogen, NASA lacked a comprehensive system for detecting a leak for much of its career. Part of hydrogen's danger is that it gives off low radiant heat, meaning its flame is invisible in daylight. NASA came up with a rather creative solution for the issue. During the Apollo missions, scientists and engineers would simply walk through the facilities with a long broom held out in front of them. When the broom touched the invisible burning hydrogen, the end would suddenly combust and they could mark another area which had dangerous gas within it. It was low-tech — but it worked.
During the Space Shuttle years, NASA made use of more complex sensors to detect leaks and ultraviolet cameras to spot flames already burning. These measures, while more effective than just waving a broom around, still did not provide an immediate visual indicator of a leak to those on the ground. The agency needed a new technology to spot leaks, one that could be precise and immediate.
Commercial hydrogen tape being used to detect a leak, one of many technologies developed by NASA and now available to the public. (Source: ASI Magazine)
Working in conjunction with the Florida Solar Energy Center, and making use of a preexisting Japanese patent, scientists at NASA developed a chemochromic tape that changes color in the presence of hydrogen. Hydrogen reacts with the compounds suspended in the outer layer of the tape, indicating a leak. It was first used in 2007 during an Endeavour shuttle flight and has since found a variety of industrial uses in the private sector.
Hydrogen leaks continue to be a concern. The second attempted launch of the recent Artemis 1 mission was aborted when a persistent leak could not be shut off. Although systems for detection and management have advanced, NASA faces the same dilemma it did during the Apollo days: the most efficient fuel is also the most dangerous and the easiest to leak. As NASA and the other space agencies ready more missions in the coming years, special attention will have to be paid to this old problem. In this case, it really is rocket science.
Klebanoff L. Hydrogen Storage Technology: Materials and Applications. CRC Press; 2012. doi:10.1201/b13685