Space Propulsion | Development of U.S. Closed-loop Kerolox Engine Stuck in 2nd Gear

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WASHINGTON — In the past decade and a half, every U.S. agency that operates spacecraft has come to depend on one particular style of Russian-designed, kerosene-fueled rocket engine, made by former Soviet design bureaus and sold to U.S. companies for use on American rockets.

This international supply chain, forged in the late 1990s to bring NPO Energomash’s RD-180 to U.S. shores for Lockheed Martin’s Atlas 3, has bridged gaps between former Cold War rivals and produced rockets so reliable that the U.S. military buys them in bulk. NASA, likewise, is relying on Russian-built closed-loop kerosene-fueled engines — but not the RD-180 in particular — to launch eight cargo delivery missions to the international space station.

The buy-international model works so well that even an executive with the company working on an American alternative to the RD-180 — which has powered 43 flawless space launches since it made its U.S. debut on Lockheed Martin’s Atlas 3 rocket in 2000 — does not see much urgency on anyone’s part to bring such an engine to market.

“We don’t see a good business case for a pure commercial development of one of these engines,” Julie Van Kleeck, vice president of space programs at Sacramento, Calif.-based Aerojet Rocketdyne, told SpaceNews in a July 9 phone interview. “Not today.”

Nor is the government in a hurry to put up the funds, Van Kleeck said. 

But it was, once. 

In 2010, the Obama administration said it wanted to make development of a 1 million pound-thrust, closed-loop kerosene-fueled engine a national priority. However, Congress preferred a new rocket based on shuttle-derived systems, and the White House had to compromise.

Thanks to Soviet-era advances in metallurgy and combustion stability, Russian-style closed-loop kerosene engines are the best of the breed for liquid-fueled first stages. They run hotter and more efficiently than the configuration used, for example, by Space Exploration Technologies Corp., which in 2006 became the only U.S. company in decades to fly a kerosene-fueled engine it built from scratch. 

“The closed-loop combustion cycle is more efficient in that it yields about 15 [percent to] 20 percent greater thrust than the open-loop cycle for the same amount of propellant flow,” said Dale Thomas, associate technical director at the Marshall Space Flight Center in Huntsville, Ala., and head of the nearby National Institute for Rocket Propulsion Systems.

Put another way, “it allows the [rocket] stage designer to pack more energy into a smaller package,” Greg Pech, director of the engines, motors integration and product delivery team at United Launch Alliance (ULA) of Denver, said in a July 9 email. That alone is not a game-changer, Pech said, but such engines would make bulk orders cheaper, compared with the price of ULA’s Delta 4, the company’s all-American alternative to Atlas 5.

ULA is still buying imported RD-180s from a company called RD Amross, a joint venture of NPO Energomash and United Technology Corp., former parent company of Pratt & Whitney Rocketdyne. RD Amross was not conveyed to Aerojet as part of its June 13 takeover of Pratt & Whitney Rocketdyne. 

Testing, 1 … 2 …

In 2007, the Air Force Research Laboratory gave Aerojet a $110 million contract for preliminary work on an advanced hydrocarbon booster engine, which the service said should be capable of generating up to 1 million pounds of thrust — a little more than the RD-180 generates at sea level.

Van Kleeck said Aerojet Rocketdyne will leverage some of the work it did for the Air Force to develop a 500,000 pound-thrust, closed-loop kerosene engine that could be used as a side-mounted booster for the Space Launch System (SLS) NASA is working on. Competition for the side-mounted boosters would not begin until 2015 or 2016 — around the time Aerojet is scheduled to test-fire the new engine, according to Thomas. The first SLS flight that needs new boosters, meanwhile, would not be until the mid-2020s. Launches scheduled for 2017 and 2021 would use shuttle-derived solid-fuel boosters for raw power off the pad.

If Aerojet Rocketdyne brings its new engine into production, it could have a customer waiting in Orbital Sciences Corp. of Dulles, Va., which is looking for an alternative to the AJ-26 engines Aerojet sold it for the first 10 flights of the Antares medium-lift rocket — the vehicle at the heart of Orbital’s eight-flight, $1.9 billion space station cargo delivery contract with NASA. The AJ-26 is a refurbished, upgraded version of the kerosene-fueled NK-33 engine developed for a failed Soviet Moon rocket called N1, and Orbital is concerned that the remaining stockpile of refurbishable NK-33s is too small to depend upon long term.

As a replacement, the RD-180 is high on Orbital’s list. So high, in fact, that the company in June sued ULA for restricting the commercial sale of the engine. Currently, ULA is the sole U.S. buyer of RD-180 engines under an exclusivity agreement that one of its parent companies, Lockheed Martin, secured in 1997 as a condition of funding the RD-180’s development in Russia.