Sunday, June 12, 2022

The Coming of Age for Liquid Hydrogen Systems: 1960 - present

Apollo fuel cell (left); shuttle external tank (middle); new LH2 dewar tank at KSC under construction

In my last post I wrote about the use of hydrogen in the development of jet engines in the 1930s, and successful test flights with a liquid hydrogen jet aircraft in the 1950s. However, the applications where liquid hydrogen (LH2) systems were fully deployed at very large scale were in the space program and rocketry [1].

Large Scale Liquid Hydrogen Systems Deployment

The initial use of LH2 in rockets was with the Centaur which was first flown in 1962. Integrated with several first stages over the years, it evolved into a workhorse upper stage with over 245 launches and counting.

During the Apollo program, the massive Saturn V rocket that sent astronauts and payloads to the moon used LH2 in its second and third stages. The second stage held 260,000 US gallons (984 000 liters) of LH2; the third stage had 66,770 US gallons (252 750 liters) of LH2 onboard.

The Space Shuttle stored its hydrogen in the enormous brownish-orange External Tank (ET) recognized by anyone who watched a launch live or on video. Loaded into the ET for every shuttle launch was 390,000 US gallons (1 476 000 liters) of LH2.

Contemporary rockets that use LH2 include the European Space Agency's Ariane 5 with over 110 launches. NASA's new Space Launch System (SLS) also uses LH2 and is expected to perform its first launch in the second half of 2022.

All of the above use cases of LH2 over the past six decades has required extensive ground support systems and associated logistics. Large scale production, distribution, storage, fueling, and other operations are well established for LH2 as a result [2].

Hydrogen Fuel Cells

Propulsion wasn't the only use of hydrogen in the space program. The Apollo program used hydrogen fuel cells for power, heat, and potable water for the astronauts [3]. Likewise, the Space Shuttles relied on hydrogen fuel cells to provide power during every one of the 135 missions they flew.

NASA also developed regenerative (i.e., reversible) fuel cells that can operated "in reverse" as an electrolyzer. This technology enabled the use of a single unit to generate hydrogen from water when a power source is available (e.g., solar panels during the day), and then generate electrical power in fuel cell mode when needed (e.g., at night).

Hydrogen fuel cells have more than double the efficiency compared to combustion processes for generating electricity. Yet they retain a key advantage of traditional fossil fuels - the capability to store and distribute large quantities of fuel to be used when needed for energy production.


[3] "Power and Water the NASA Way", Apr 26, 2016.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind liquid, slush and gaseous hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology based start-ups; and provided R&D and engineering support to hundreds of organizations. Matt has three patents and more than 50 publications including the Cryogenic Fluid Management report series. More about him can be found here.