Space Propulsion | Moog Sees Higher-thrust Liquid Propellant Engine as Right Fit for Mars Missions

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SAN FRANCISCO —With the backing of the U.K. Space Agency and Enterprise Ireland, Moog Inc. is leading an effort to develop a liquid propellant engine capable of providing higher thrust with less propellant than existing propulsion systems. 

The goal is to create a 1,100 Newton-class engine for planetary missions that can send more scientific instruments into orbit around Mars than is possible with 500 Newton-class engines. The engines will be efficient enough to save 150 kilograms of propellant on a 3,500 -kilogram spacecraft, Moog officials said.      

“Interplanetary missions are becoming ever more ambitious in terms of scale and the spacecraft sent to planets are becoming larger,” said Lolan Naicker, Moog’s lead engineer for the High Thrust Apogee Engine (HTAE). “To accommodate more science instruments on a spacecraft, you need to trim down all the service aspects of that spacecraft. For instance, the propulsion design needs to be reduced in mass.”

HTAE development work is being conducted under the European Space Agency’s (ESA) Mars Robotic Exploration Program, an initiative designed to pave the way for European contributions to future international Mars exploration missions. Within that program, ESA is funding development of key mission technologies including HTAE. 

“One thing we noticed with existing propulsion: Sizing is not ideal for large Mars missions,” said David Perigo, chemical propulsion engineer at ESA’s European Space Research and Technology Center in the Netherlands. “Thrust for standard apogee engines is a little low.”

That was not a problem in previous missions, including Mars Express, because of the small size of the spacecraft, Perigo said. As spacecraft sent to Mars approach the 4-ton mark, however, the task of moving into the planet’s orbit becomes far more difficult, requiring an exceptionally long orbit-insertion burn fueled by 300 kilograms of propellant more than missions traditionally need for an impulsive burn at the perigee point. 

To make room for that fuel, missions planners would need to reduce the mass of the scientific payload. Instead, they are seeking a higher-thrust engine capable of performing the maneuver with less propellant. 

The team led by Wescott, U.K.-based Moog ISP began designing the bipropellant apogee engine in late 2011. A preliminary design review for HTAE is scheduled for late 2013, followed by a critical design review two years later, said Ronan Wall, Moog’s HTAE program manager.

By 2016, HTAE will be available for use on Mars exploration missions or other jobs that might require a similar capability such as electric propulsion missions featuring a chemical propulsion system to move the spacecraft into the correct orbit or “green” monopropellant engines that require higher flow rates than existing bipropellant engines, Wall said.

Moog is starting with a blank slate in its HTAE design. Instead of seeking to make evolutionary improvements to engine components, Moog engineers are surveying a wide range of materials, technologies and manufacturing techniques. For example, Moog plans to test three dozen injector designs and three combustion chamber designs. Company engineers also are looking at various materials that could be used to create HTAE’s high-temperature combustion chamber, including platinum alloys, composites and ceramics. 

“We want to see what we can pick up in terms of truly optimizing these engines,” Wall said. “If we get the right combination of injectors and chambers, we will be feeding that down into our existing products and increasing their capability as well as delivering the best thing we can for ESA.”

The HTAE will be fueled by monomethylhydrazine and mixed oxides of nitrogen. “We want to fully understand apogee engines that use that particular propellant combination,” Naicker said.

Moog ISP, a company formed in July 2012 when Moog acquired American Pacific Corp.’s In-Space Propulsion business, also is designing new valves for HTAE at its facility in Dublin. The challenge facing engineers is to create valves capable of handling almost twice the flow rate of Moog’s existing LEROS liquid apogee engine without making significant changes to the size or mass of those valves, said Martin Houston, Moog’s lead engineering for HTAE valve development.

That type of advanced technology development work is welcomed by Enterprise Ireland, a government organization that supports Irish trade and manufacturing. “Part of our strategy is to build up these technologies that could be used across a range of mission opportunities,” said Tony McDonald, Enterprise Ireland’s program manager for space industry activities. “That includes cooperation in developing advanced technology and materials. HTAE fits in very well with that strategy.” 

Sue Horne, exploration chief for the U.K. Space Agency, said her organization is providing support for HTAE because the technology developed will make Mars missions more capable. “We will get a greater return for our investment in future Mars missions,” Horne said.

In addition, the U.K. Space Agency expects the program to help support its economic goals. “By doing this, we are developing capabilities and technologies that will help the economy to grow,” Horne said. “Science is underpinning our growth agenda.”