October 16, 2021. By Kolemann Lutz
Researchers at NASA Kennedy Space Center (KSC) developed the IRAS technology with zero loss storage and transfer, remove system heat loads, propellant densification, in situ liquefaction.
While liquid hydrogen and liquid oxygen are excellent, high-performance rocket propellants, they are cryogenic -- meaning super cold. The oxygen in liquid state is minus 297 degrees Fahrenheit and hydrogen is minus 423 degrees Fahrenheit. Because of ambient temperatures, storing these commodities is like storing ice in an oven. Liquified gases like hydrogen, nitrogen, liquid natural gas, oxygen, and argon are usually stored below their boiling points.
The previous storage tanks NASA KSC was using were vacuum-jacketed with three-foot-thick perlite (amorphous volcanic glass, 70–75% Silicon Oxide:SiO2) insulation. Although, 50% of the liquid hydrogen purchased to fuel the space shuttle's was lost due to boil off evaporation. As significant cryogenic losses come from compressors, turbines, and heat exchangers, novel methods are sought to optimize heat transfer.
The storage tank illustrated on the left, outlines how LH2 and LOX have been stored at KSC for over half a century. The new tank holds 1.25 million gallons (4731 cubic meters) and Integrated Refrigeration and Storage (IRaS) and glass "bubble" thermal insulation in the space around the inner vessel. An integrated heat exchanger with a cryogenic refrigeration system helps remove heat. "IRaS is important because it allows unprecedented control in storing cryogenic liquids. The normal evaporation rate or 'boil off' can now be a thing of the past,” mentioned by Dr. Bill Notardonato, a principal investigator in Kennedy's Exploration Research and Technology Programs.
New glass "bubble" insulation is also being tested to replace perlite powder. 2015 Field tests in Mississippi showed that liquid hydrogen losses through boil off can be reduced by 46%. With IRaS storage systems, liquid boil off can be eliminated altogether, which is important for larger storage tanks such as NASA’s cryogenic tank that holds 1.25 million gallons of LH2.
Multilayer insulation (MLI) or called superinsulation) provides passive thermal shielding and is composed of reflective films (usually aluminium or aluminized polyester film) separated by insulating interlayers (polyester, glass-fibre nets, or paper). The reflecting layers reduce heat transfer by radiation, the insulating interlayers reduce heat transfer by conduction between reflecting layers, and the high vacuum reduces convection and residual gas conduction.
As multi-layer insulation for cylinder tanks can be sensitive to thermal shock and vibrations during transport, typical thermal expansion and contraction of the tank walls can compact perlite, creating cold spots and increasing boil off. The spherical shape of hollow 3M glass bubbles don’t experience compaction or settling caused by vibrations or thermal expansions and contractions and can be installed into existing annulus around MLI insulation.
The high strength-to-density ratio of 3M glass bubbles 1.7 MPa strength and density of .125 to .38 g/cc means they can withstand the forces exerted during cryogen filling, emptying, and thermal cycling. 3M™ Performance Additive iM30K is the world's first hollow glass microsphere capable of withstanding injection molding and extrusion pressures of 30,000 psi.
The spherical shape, low density, volume, and thermal performance of 3M glass bubbles reduce both the weight and volume of the insulation. The 3M Glass bubbles also provide excellent H2O and oil resistance for underwater applications and have found use in a variety of fields: Construction, Insulation and Buoyancy, Mining, Paints and Coatings, Rubber and Plastic, Transportation.
Moreover, cryogenic liquids or superconducting machines such as pulse tube cryocoolers with high 120Hz frequency and high 5MPa pressure (Radebaught, 2012) can be used to
provide low mass compressors and longterm, reliable cooling to develop high temperature superconducting (HTS) generators, magnets, coils, sensors, and motors.
While Zero Point Boil Off (ZBO) keeps cryogenic liquids indefinitely by matching the tank heat leak, IRAS goes further to provide full control of the state of the fluid: gas, liquid, densified liquid, or slush. The change was like going from storing ice in a foam cup to keeping it in a freezer. Similar to how a freezer regulates temperatures, spending about 15 cents with in electricity with IRaS recovers $1 in hydrogen.
As the SLS core rocket is designed to send humans and payloads beyond Earth to Moon and Mars, the SLS core stage and in-space stage requires 730,000 gallons of liquid hydrogen and liquid oxygen to fuel the four core stage and single upper stage engine.
A fully configured Starship with booster will use about 1,000 tonnes of liquid CH4, which can be stored at a much warmer and more convenient temperature of -161.6° (-260 deg F), recovering energy and costs.
A combination of 3M glass bubbles and IRaS hold great potential to impact cryogenics for generations and to store significant quantities of liquified gases on the surface of Mars, Moon, and beyond.
