Steaming into space

NASA, the US Air Force and their aerospace contract team have successfully completed testing of two key rocket engine components destined for use in a hydrogen-fuelled staged combustion rocket engine.

The tests – of a new, liquid-hydrogen turbopump and an oxidiser preburner – are part of a project called the Integrated Powerhead Demonstrator, or IPD.

The project is a joint venture between NASA’s Next Generation Launch Technology program, managed for the Agency at the Marshall Space Flight Center in Huntsville, AL and the Integrated High Payoff Rocket Propulsion Technologies program, managed for the Department of Defense by the US Air Force Research Laboratory at Edwards Air Force Base, CA.

Both tests are part of studies intended to lead to the development of a hydrogen-fuelled, full-flow, staged-combustion rocket engine with 250,000-pound thrust – the first of its kind. The engine will employ dual preburners that provide both oxygen-rich and hydrogen-rich staged combustion, which will help to cool engines during flight, achieve higher engine efficiency and reduce exhaust emissions.

The project is intended to address two major technological challenges – turbine life and bearing wear – which traditionally have limited performance among rocket engines.

By sending all of the propellant flow through the turbine, the same amount of energy can be extracted with a lower-temperature gas than that used by the current shuttle – thus reducing the likelihood of material fatigue caused by sustained high temperatures.

The high-performance IPD turbomachinery will also include hydrostatic bearings that fully support the rotor of both the fuel and oxidiser pump. Because the hydrostatic bearings actually cause the rotor to float on a layer of liquid during operation, bearing wear only occurs for a few seconds during engine startup and shutdown. Rocket turbomachinery, in comparison, typically uses ball bearings or roller bearings. Minimizing operational contact eliminates bearing wear as a major life-limiting factor for the turbomachinery.

The liquid-hydrogen fuel turbopump itself was developed for NASA and the Air Force by the Rocketdyne Propulsion and Power division of the Boeing Company of Canoga Park , CA. The turbopump test series, conducted at the Stennis Space Center, was completed on October 29.

The turbopump is designed to provide high-pressure hydrogen to the rocket engine thrust chamber, enabling the combustion process and generating thrust. The turbopump extracts energy from hot gases, which are generated by the fuel preburner and flow through the turbine, causing the turbopump rotor to spin at more than 50,000 rpm. As the rotor spins, an impeller attached to the other end of the shaft pumps the hydrogen to pressures greater than 6,600 psi. These high pressures are necessary to generate the 3,000 psi combustion gases in the thrust chamber, which expand through the chamber and nozzle to produce 250,000 pounds of thrust.

The design and technologies of the fuel turbopump address key life limitations of current reusable rocket engines, and is intended to achieve a lifespan of 200 flight missions and 100 flights between periods of engine refurbishment – 10 times the current capability of reusable rocket engines.

Testing of the oxidiser preburner was completed on October 28 by component designer Aerojet Corporation at its Sacramento, CA, facilities.

The oxidizer preburner – which initiates the combustion process – is designed to generate oxygen-rich steam for use by the oxygen turbopump’s turbine. The preburner burns a large quantity of liquid oxygen with a small quantity of hydrogen to produce this steam, which then mixes with additional hydrogen fuel to be burned in the main combustion chamber.

The preburner is the first flight-capable, oxygen-rich preburner developed in the US for a large-scale engine. The use of oxygen-rich steam to power the oxygen turbopump is intended to increase the safety of engine system operation, limiting seal failure between the pump and the turbine that could leak extremely hot gases into the turbine and cause them to burn prematurely.

Integrated testing of both systems is scheduled to begin in late 2004 at NASA’s Stennis Space Center near Bay St. Louis, MS.

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