NASA Invests in Cryogen Storage Mission Concepts


WASHINGTON — NASA wants to fly a mission in 2015 that will demonstrate core technologies needed for long-term storage and transfer of cryogenic rocket fuels in space — a capability the agency says is critical for future crewed missions beyond Earth orbit.

The U.S. space agency on Aug. 5 announced that four companies are getting up to $600,000 each to study mission concepts for demonstrating in-space storage and transfer of liquid hydrogen and liquid oxygen. Awardees must design a demonstration mission that costs between $200 million and $300 million, NASA said.

In particular, NASA wants to advance the state of the art for in-space storage of liquid hydrogen — the most troublesome cryogen to store in space because of its relatively low boiling point of approximately minus 253 degrees Celsius.

“What we’d like to demonstrate in space in the next few years is the ability to store liquid hydrogen for several months,” said Chris Moore, deputy director of NASA’s Advanced Capabilities Division. The ability to do so would constitute “a major advance because we can only store it for several hours now,” he said.

Moore’s division is part of NASA’s Exploration Technology Development Program, which is funding the studies. The Glenn Research Center in Cleveland is managing the contracts, which were awarded to Analytical Research Associates, Huntington, Ala.; Ball Aerospace & Technologies Corp., Boulder, Colo.; Huntington Beach, Calif.-based Boeing; and Lockheed Martin Space Systems in Denver.

Prescribed technical objectives include the capability to store liquid oxygen with “zero boil-off” and liquid hydrogen with “minimal boil-off” in space. Studies also must address cryogenic fluid transfer in microgravity, including “bubble-free” transfer of super-cooled liquid propellants.

Companies also must propose ways to measure the flow of cryogens in space, and police storage systems for leaks, according to an amended solicitation that NASA released in April. Hydrogen is notorious for its propensity to leak — something scientists ascribe to the very small size of the hydrogen molecule.

The basic mission architecture to prove the space-worthiness of advanced cryogenic storage technologies will require “a spacecraft of some sort,” said Patrick McKenzie, business development director for exploration at Ball Aerospace. “We’re not talking the behemoth, billion-dollar spacecraft. We’re talking the smaller type spacecraft that … will serve as the platform for the experiment itself.”

Ball, as part of its concept study, might include something along the lines of the Next Generation Satellite and Commodities spacecraft — a vessel the company successfully flew in 2007 as part of the Orbital Express on-orbit satellite servicing mission for the U.S. Defense Advanced Research Projects Agency.

NASA’s Aug. 5 announcement again stirred up talk in some quarters of the space community that the agency was preparing to ramp up the development of space-based propellant depots — so-called gas stations in space from which passing spacecraft refill their fuel reservoirs.

Depot supporters have proposed placing depots in low Earth orbit, at gravitationally stable Lagrange points between the Earth and the Moon, and near Mars. Keeping a supply of accessible cryogenic propellant in space would allow high-energy rockets fueled by cryogenic fuels to launch from Earth with less fuel — and, consequently, less mass — and refuel en route to their destinations.

Moore downplayed the idea that the Aug. 5 award was directly tied to an agency initiative to develop propellant depots.

“It’s not really looking at ultimate applications, just testing the enabling technology,” he said.

Notably absent from the NASA solicitation for these mission concept studies was any mention of the autonomous on-orbit rendezvous and docking flight systems that would be necessary for any sort of propellant depot.

That technology “is required for space depots, but it’s not required for the fundamental technologies that NASA’s looking for in this [study],” said Al Herzl, program manager for Lockheed Martin’s demonstration mission concept studies for in-space cryogenic propellant storage and transfer.

Moore, meanwhile, pointed out the applicability of long-term cryogen storage to NASA’s official deep-space exploration strategy: launching astronauts — and all the propellant they need — on a planned heavy-lift rocket called the Space Launch System (SLS).

NASA is mostly interested in long-term cryogen storage because to pay a visit to a near-Earth asteroid, or to Mars, “we need to be able to store these cryogenic propellants for up to a year at a time,” said Moore.

SLS, according to the configuration described by NASA Administrator Charles Bolden in a July hearing before the House Science Committee, will closely resemble the cancelled Ares 5 cargo rocket planned for the Constellation program.

SLS would use both shuttle- and Apollo-derived components, including the space shuttle’s main engines and, at least initially, solid boosters. A planned cryogenic upper stage would add a J-2X engine, an evolved version of the Saturn 5 upper stage. The largest SLS configuration would be capable of lifting 130 metric tons to low Earth orbit.

SLS would therefore be capable, out of the box, of performing both the uncrewed lunar flyby Bolden says the agency is planning for 2017 and a crewed version of the same mission now slated for the early 2020s.

SLS would not, however, be able to take an astronaut crew on a return trip to an asteroid without “some sort of substantial investment in technology” said Pat Troutman, an engineer at NASA’s Langley Research Center in Hampton, Va.

The Aug. 5 announcement represents one fork in the road NASA is exploring for this future investment. Another alternative under consideration is advanced solar electric propulsion, said Moore at NASA headquarters.

Troutman said that investing in long-duration, near-zero boil-off cryogen storage instead of advanced solar power would yield the greater benefit. Although he said “the jury’s still out” about whether solar or cryogenic propulsion is better suited for near-Earth asteroid exploration, cryogenic propulsion has cross application to a Mars mission that solar power lacks.

“If we invest in solar electric earlier, we don’t have to do zero boil-off for asteroids. But then we have to do it again later for Mars anyway,” said Troutman.