WORLD’S LARGEST DOUBLE WALL LIQUID HYDROGEN SPHERE
Ever since the outset of NASA’s push for manned missions to Mars and beyond, the NASA engineers knew they had some growing pains to overcome: all of their launch pad infrastructure was designed and built to support the early rocket and shuttle programs. Traveling further into space than ever before will require larger rockets, and larger rockets require higher fuel consumption. Understanding this, NASA decided it was time to invest in a launch pad makeover. Headlining this renovation is the 1.25M Gallon Liquid Hydrogen Double Wall Sphere, the largest double wall sphere in the world.
Designing a cryogenic pressure vessel for launch operations is no simple task. Since the LH2 Sphere is hundreds of yards from the rocket, pressure building coils are used to build pressure in the sphere and piston the LH2 to the rocket. There are no pumps in the transfer system, so a substantial amount of pressure is needed to overcome the head loss in the piping and keep the flashing to a minimum. In addition, the LH2 is so cold (-423F) that the operators do not transfer the fuel from the sphere to the rocket until immediately before liftoff as a means of protecting certain rocket components. The NASA LH2 sphere is designed to 105 PSIG and rated for temperatures less than -450 degree F, driving the inner sphere stainless steel to thicknesses over 1.4″.
One of NASA’s highest priorities in the design of the sphere was the vessel’s boil-off performance. This led to the design and implementation of two independent, original systems to combat boil-off, both being the first of their kind in application. One of these
systems is a heat exchanger inside the inner sphere that introduces helium from a cryogenic refrigerator to supercool the hydrogen. The second is the use of microsphere insulation, rather than industry standard perlite, that is conveyed into the annular space between the inner sphere and outer jacket. After all the insulation is transferred into this space, a high vacuum is established to further reduce the heat transfer between the two concentric spheres. These two systems combined will virtually eliminate product boil-off, with the potential to save NASA millions of dollars over the lifespan of the vessel.
From the Florida Summer heat to multiple hurricanes, the site conditions for construction were never ideal. The entire construction team was required to evacuate site for hours at a time, sometimes days, when SpaceX would launch from Launch Complex 39A. There were also a few dress rehearsals for the Artemis Program on Launch Complex 39B that prevented construction for extended durations. Even after these unpredictable factors, the sphere was erected and tested well within the budget.
Since this was the first double wall sphere designed and built since the 1990s, much of the testing was pioneered by our engineers and NASA. The most notorious of these tests was the cold shock test: a rapid introduction of cryogenic product to the inner sphere to ensure the steel reacted as expected and there was no unexpected low temperature embrittlement. Helium leak testing was also performed on every welded joint on the inner sphere, outer sphere, and interconnecting piping, making this double wall sphere the largest vessel to be 100% helium leak tested.
The notability of the NASA LH2 sphere is not merely derived by its role in interplanetary travel. Rather, the stage has been set to scale green hydrogen storage so that interplanetary travel may continue to be driven by human curiosity instead of necessity.
ASME Pressure Vessel
- 1.25M Gallon Double Wall LH2 Sphere
- Cape Canaveral, FL
August 1, 2022
ASME VIII, Div 2
Steel Tonnage Used