Highlights from AIAA Propulsion and Energy 2016

Green aviation

Turboelectric propulsion, which uses fuel-burning engines to generate electricity, has the best shot at making a big dent in commercial aviation’s carbon footprint within the next 30 years rather than batteries or hybrid engines.

That was the key finding presented by the federal Committee on Propulsion and Energy Systems to Reduce Commercial Aviation Carbon Emissions, which is advising NASA on research priorities.

The committee concluded that turboelectric propulsion, coupled with distributed propulsion and boundary layer ingestion, could lower emissions and fuel burn by at least 20 percent compared with today’s large commercial aircraft, AIAA’s Ben Iannotta reported.

“If they screw up, fire them. If they succeed, give them the things they need to get their job done.”
Bran Ferren, chief creative officer of Applied Minds, on encouraging innovation

No current “battery chemistries” are capable of powering commercial jets carrying 100 passengers or more, said Alan Epstein, vice president for technology and environment for Pratt & Whitney. What’s more, the U.S. lacks “megawatt class” facilities necessary for advanced research on battery propulsion, said Karen Thole, a committee co-chair and professor of nuclear and mechanical engineering at Penn State.

Thole cautioned that the committee’s message was not, “Stop working on batteries.”

On the topic of engine technologies, including nacelles and heat-tolerant internal coatings, Epstein said ultimately, propulsion and aircraft designs will need to be considered together as a system, even if that was not the committee’s focus.

The committee also lauded the potential of sustainable alternative fuels to reduce aviation’s carbon footprint. That’s critical, said Steven Csonka, executive director of the Commercial Aviation Alternative Fuels Initiative, because “we expect to be using fuel in aircraft at least for the next five decades.”

Reusable rockets: Holy Grail or chasing our tail?

Space visionary Wernher von Braun was the first to imagine reusable launch systems, once proposing to build components that could be reused nearly 1,000 times to send crews to Mars.

That von Braun’s dream is possible has been borne out by the X-33, X-34 and X-37, panelists told a capacity crowd, reported AIAA’s Duane Hyland.

Experts agreed that reusable systems — especially from the perspective of liquid engine technology — wasn’t a question of feasibility, but rather, as Doug Bradley, chief engineer of advanced space and launch at Aerojet Rocketdyne, put it, “an inability.”

“I think you should learn to say yes to the point of discomfort.”
Rex Geveden, chief operating officer of BWX Technologies, on one way to propel your career

Bradley meant that the need to explore space more cheaply will drive the demand for reusable launch vehicles.

Ben Goldberg, vice president of science and engineering for the Propulsion Systems Division at Orbital ATK, cautioned that reusing systems may not always make sense due to costs and mission needs. For instance, an ocean landing, due to the corrosive nature of seawater, might not make sense for a reusable system, while a land touchdown may.

Reusability in space systems is at a crossroads, but the panelists predicted a bold turn toward greater and greater reliance on reusable systems, making the goal of cheap and dependable spaceflight a reality.

Nuclear-powered space exploration

As the U.S. continues to explore deeper reaches of the solar system, it’s becoming apparent that nuclear power — either in the form of radioisotope power systems, fusion reactors or fission reactors — can play a significant role in powering those missions.

Duane Hyland reported on a panel discussion on how going beyond solar-powered space missions could make venturing to farther edges of the solar system practical and reduce transit times.

“Once you get to Jupiter, you have 1/25th of the sun’s solar rays available to you, and when you get to Saturn, it’s 1/100th of the rays,” noted Leonard Dudzinski with NASA’s Science Mission Directorate.

“It will be China that does it.”
Pierre Chao, founding partner of Renaissance Strategic Advisors, on who will break the Boeing-Airbus duopoly in commercial aviation

Rex Geveden, chief operating officer for BWX Technologies, said nuclear-fueled spacecraft could cut the journey time between Earth and Mars by a month or two.

Nuclear power’s high cost, however, could limit its use in space. The U.S. space program uses plutonium-238, which is available only from Russia. It costs $3 million per kilogram, said John Casani, an independent consultant formerly with NASA’s Jet Propulsion Laboratory.

Dudzinski said that price tag means missions would cost $400 million on average, making them unattractive to most planners. Panelists recommended switching to uranium, which costs just $2,500 per kilogram and is widely produced and easily integrated.

Nuclear power faces other disadvantages. They include heavier weight relative to energy output, public wariness and a lack of visionary advocates.

Getting beyond additive manufacturing’s “Betamax” stage

Additive manufacturing has made significant inroads with rocket engine makers. The next steps are to define standards and inspection processes to ensure confidence and wide acceptance of additively-manufactured components.

“We’re in the Betamax-tape part of this additive thing,” said Jay Littles, director of advanced launch vehicle propulsion at Aerojet Rocketdyne, referring to the 1970s-era Sony videotape standard that was beat out by VHS. “It’s going to be interesting to see where we go over the next decade.”

Ben Iannotta reported that several panelists pointed out obstacles to greater use of additive manufacturing, which uses laser or electrons to fuse metal powder into parts.

Elizabeth Robertson, leader of the Liquid Engine Systems Branch of NASA’s Marshall Space Flight Center in Alabama, said that until inspection issues are figured out, there may be limits on “human rating” of additively manufactured parts, referring to the ratings NASA requires before trusting technologies to launch people.

“You’ll have no regrets, and you’ll be able to sleep well at night.”
Allan McDonald, retired manager at Morton Thiokol, builder of Challenger’s solid rocket motors, on speaking up about safety concerns

Littles agreed that quality assurance is a big challenge, given the complex geometries and larger sizes of such components.

Littles said other goals include making larger components and understanding the performance of specific additive manufacturing machines.

“Additive really does open up the design window, but there’s also a lot of stuff that you can’t do — geometries to avoid,” Littles said.

On the other hand, Robertson said, fewer part counts translates to “fantastic” reliability.”

She recounted that in 2012, NASA decided to make components for a prototype engine to demonstrate additive manufacturing. Managers saw a 30 percent reduction in cost and part reduction from 250 to six.

Robertson said the quality of additive manufacturing currently varies more depending on the individual worker instead of the company. “Right now, additive is still an art.” ★

Highlights from AIAA Propulsion and Energy 2016