P&W offers Russian-based engine for NASA's SLI

GRAHAM WARWICK / WASHINGTON DC

Pratt & Whitney is proposing a Russian-based rocket motor for NASA's Space Launch Initiative (SLI) to develop a second-generation reusable launch vehicle (RLV) to replace the Space Shuttle. The move comes as attention begins to focus on a two-stage vehicle with a kerosene-fuelled flyback first stage.

P&W's proposed AR-1000 liquid-oxygen/kerosene engine is a reusable derivative of the RD-180 rocket motor produced by Russian Energomash under a joint venture with the US manufacturer. The RD-180 powers the Lockheed Martin Atlas III and V expendable boosters, but was originally derived from the RD-170 engine designed to power Russia's Buran reusable launch vehicle.

Under the initiative, P&W is also working on the Cobra liquid-oxygen/liquid-hydrogen engine, and the lower-thrust RLX, in a joint venture with Aerojet. Originally, they were also teamed to develop the Ajax liquid-oxygen/hydrocarbon rocket motor, but split last year to offer competing kerosene-fuelled engines. Boeing Rocketdyne is also offering hydrogen and hydrocarbon solutions.

Interest is shifting towards a kerosene-fuelled first stage as NASA and the US Air Force complete a 120-day study into co-operating on RLV development, says P&W vice-president, booster propulsion systems, Rick Bachtel.

Advantages of kerosene over liquid hydrogen include easier storage and handling, compatibility with the USAF's jet-fuel infrastructure and higher density, which results in a smaller, albeit heavier vehicle, that is easier to fly back and handle on the ground, says Bachtel.

Because NASA and the USAF require a US-built engine, Energomash and the Russian government have agreed to license the RD-180 technology to P&W, says Bachtel. The US company plans to redesign the engine with a single combustion chamber for simplicity and to make design changes to extend life, increase redundancy, improve maintainability and introduce health monitoring.

Of the three companies developing architectures for NASA's second-generation RLV, Lockheed Martin has already settled on a kerosene-fuelled first stage and hydrogen-fuelled second stage, Bachtel says.

Although NASA initially favoured an all-cryogenic solution, recent studies have favoured a kerosene-fuelled first stage for operability reasons, he says. Boeing and Northrop Grumman are studying both approaches.

NASA is expected to narrow the number of second-generation RLV architectures under development to three, one from each company, later this year.

Source: Flight International