Ultracold Liquid Hydrogen May Be Fuel of the Future

NASA has wrapped up testing on a new cooling system that supercools hydrogen to -423°F. It’s housed in a shuttle-era storage facility engineers saved from demolition five years ago at the agency’s Kennedy Space Center in Florida and thereafter transformed into a test site for new ground operations demo units.

The system is comprised of a 33,000-gallon liquid hydrogen storage tank recycled from the Titan Centaur program, with an internal cold heat exchanger supplied from a cryogenic refrigerator. The refrigerator, chiller and associated controls are housed in a metal storage container for insulation and to protect them from the corrosive sand and salt environment.

A team of civil servants and contractors from the center’s Cryogenic Test Laboratory (CSA CSM) designed, installed and tested the system with key support from engineers at NASA’s Glenn Research Center in Cleveland and Stennis Space Center in Mississippi. The team conducted testing in three phases over 18 months between April 2015 and September 2016, using an increasing amount of stored hydrogen – 30, 60 and 90 percent, respectively. The tests had three primary objectives: zero boiloff, liquefaction and propellant densification.

According to Bill Notardonato, the demo unit’s principal investigator in the Exploration Research and Technology Directorate at Kennedy, a zero boiloff capability is a prime candidate for use by the Ground Systems Development and Operations Program (GSDO) at the center, potentially saving NASA millions of dollars compared to previous operations. Notardonato’s team consults with GSDO on the design of the new pad B liquid hydrogen tank and future launch pad systems.

“For Space Launch System launches, GSDO will fill the rocket’s core stage and interim cryogenic upper stage with hundreds of thousands of gallons of liquid hydrogen,” says Shawn Quinn, GSDO assistant program manager. “An important feature of the new zero boiloff technology is the potential to reduce long-term energy costs and liquid hydrogen commodity costs.”

Kennedy is preparing for the first integrated launch of NASA’s Space Launch System and Orion spacecraft. Upgrades to Launch Pad 39B, where the rocket and Orion will launch on a test flight in late 2018, include a 1.4-million-gallon hydrogen tank, a size 50 percent larger than the current tank. “The goal would be to integrate the unit’s heat exchange system into the new tank, saving GSDO money by eliminating the loss of hydrogen,” says Notardonato. “By accomplishing zero boiloff of liquid hydrogen, we could save one dollar in hydrogen for every 20 cents spent on electricity to keep it cooled.”

The new unit contains a cooling system that removes heat and vents it into the atmosphere. What is left is super-cooled hydrogen stored at -423°F. Liquefaction takes gaseous hydrogen and turns it into a liquid. Instead of the usual method of compression and expansion, the hydrogen is flowed into the tank and cooled down using helium refrigerant from a cryogenic refrigerator.

Notardonato says helium refrigerant is a good choice because it is a common refrigerant that can meet the needs of an in-situ resource utilization process in deep space.

Propellant densification, or cooling a liquid below its normal boiling point to increase the storage density, was the most challenging objective. The new system performed flawlessly, transforming the liquid hydrogen into the world’s largest volume of hydrogen slush at -435°F.

Some commercial companies, including SpaceX, are using densified oxygen for rockets, enabling cost-effective reusability of their core stages. Densifying oxygen is much easier than hydrogen, but the benefits of densified hydrogen could be far greater, according to Notardonato.

Notardonato says the next goal is to take the portable liquid hydrogen system to another center for densified hydrogen engine testing that could be used for a future commercial launch vehicle, helping to curb the cost of access to space. His team is sharing results, in parallel, with the GSDO Program and in-situ resource utilization mission planners to increase awareness of this new capability.

“It’s an exciting new technology that will benefit NASA’s Journey to Mars and has the potential to also benefit the nation’s efforts to establish alternative energy sources,” Quinn says.