Fastrac Engine -- A Boost for Low-cost Space Launch
But rocket design for the 21st century breaks with aerospace Fastrac engine hot-fire test at Marshall Center tradition and embraces a new challenge to build engines that are cheaper and better.
The new Marshall-developed engine, called Fastrac, is - true to its name - on a fast track to propelling the next generation of launch vehicles. While some of the concepts for the Fastrac engine have been around for decades, actual technology development and design began in early 1996 and the engine's first flight is planned for late 1999 - a much faster-than-usual design cycle. For example, it took nine years to develop and design the Space Shuttle Main Engine.
Fastrac is only the second American-made engine of the 29 new rocket engines developed in the last 25 years. The simple, robust, easy-to-build engine is part of the Low Cost Technologies effort, one element of NASA's Advanced Space Transportation Program managed at Marshall. The program is paving the highway to space by developing technologies that will dramatically reduce the cost of getting to space.
Using the Fastrac engine as the propulsion system for a future launch vehicle is one means to achieve NASA's goal of making space launch affordable. Because much of the research and small payload market has been "locked out" of space by high launch costs, NASA is trying to open the door to cheaper space travel. The Fastrac provides 60,000 pounds of thrust to boost payloads weighing up to 500 pounds.
Each Fastrac engine will initially cost approximately $1.2 million - about one-fifth of the cost of similar engines. That price is expected to drop even more within a few years as design enhancements are discovered and incorporated through industry participation and flight experience. As improvements are made, the cost is expected to drop to $350,000 per engine. Fastrac incorporates drastic reductions in the cost of turbomachinery, which uses pumps to increase propellant pressure and a turbine to provide energy to turn the pump. Initially, each turbopump will cost about $300,000 - one-tenth of the average cost of a current rocket engine turbopump. That cost also is expected to drop to about $90,000.
In a salient departure from traditional engine design, NASA and its business partners have adapted commercial, off-the-shelf technologies and common manufacturing methods to develop the Fastrac engine. Significant involvement by small business has aided in broadening the competition and producing lower cost hardware.
For example, Barber-Nichols, Inc. of Arvada, Colo., worked alongside Marshall engineers to design and manufacture the turbopump. The Colorado-based company is experienced in building turbomachinery for the automotive industry and chemical plants, and not traditionally associated with the aerospace industry. The company helped design a turbopump for the Fastrac engine that can be built easily using commercial manufacturing techniques.
The Fastrac engine is 7 feet long and 4 feet wide, and weighs almost 2,000 pounds.
How It Works
The engine is fueled by a mixture of liquid oxygen and kerosene, the same propellants used for the largest rocket engine ever built - the Saturn F1. Kerosene doesn't provide the same kick as hydrogen - which combines with liquid oxygen to fuel the Space Shuttle - but is cheaper and easier to handle and store.
The engine is started with a hypergolic igniter - a starter fluid that spontaneously ignites when oxygen is fed to the chamber. Once the kerosene is injected, the engine is running. The propellants are then supplied to the gas generator and thrust chamber assembly for mixing and burning.
The engine uses a gas generator cycle, which burns a small amount of kerosene and oxygen to provide gas to drive the turbine and then exhausts the spent fuel. That's the same cycle that was used on the Saturn rockets, but much more simplistic than the Shuttle engine system.
The Fastrac engine is a much simpler piece of machinery than previous American-made rocket engines. It has significantly fewer parts than engines that have driven other American spacecraft.
The reduced number of parts is a result of selecting technologies and design concepts that use simple manufacturing and assembly processes. For example, casting might be preferred over machining, because the latter method could require fabrication in several pieces due to shapes.
Chamber pressure is supplied by a single turbopump, unlike a Shuttle main engine which has four turbopumps. The Fastrac turbopump features only two pumps - one for fuel and one for liquid oxygen.
Another design feature that keeps the engine simple and inexpensive is its avionic - or electronic - control system. Typically a sophisticated, expensive part of a rocket engine, the avionics of the Fastrac engine are supplied from the vehicle's computer and are only used to open and close the valves. The thrust and mixture ratio is set during ground calibration. That's much simpler and cheaper than most rocket engine avionics, which continually modify the amount of propellants flowing into the chamber as changes in thrust are observed by on-board computers.
A typical rocket launch produces a temperature in the range of 5,500 degrees Fahrenheit, hot enough to melt almost any material. A common solution to keep the engine from overheating is regenerative cooling, which circulates liquid fuel around the engine chamber and nozzle through hundreds of feet of tediously welded tubing.
The Fastrac engine design avoids complex plumbing - opting instead to cool the chamber by charring or scorching its inside surface as the engine heats. The process is called ablative cooling. Layers of silica-phenolic composite material form a liner inside the chamber. The liner decomposes to prevent excessive heat build-up.
Nearly all of the engine's parts are reusable. The ablative chamber nozzle and the hypergolic ignition cartridge will be replaced after each flight. The chamber nozzle's protective, interior liner is damaged by intense heat inside the chamber. The hypergolic ignition cartridge must be refilled with propellant and replaced after each flight.
The first vehicle scheduled to be powered by the Fastrac engine is the X-34, a technology testbed vehicle to demonstrate key vehicle and operational technologies applicable to future low-cost Reusable Launch Vehicles (RLVs). The engine is scheduled for delivery to the X-34 program in mid-1999 and its first flight is scheduled for late-1999.
The engine is now undergoing development and reliability testing. Individual components, such as the gas generator, turbopump assembly and thrust chamber assembly, are being tested at Marshall. In August 1998 the Marshall Center shipped the first complete engine system to NASA's Stennis Space Center in Mississippi with plans to conduct about 85 hot firings. These tests simulate launch of the X-34 vehicle and potentially a first stage booster, with the tanks and engine assembled.
The Fastrac engine is being designed at Marshall and built by NASA's industry partners, including several small businesses. Major subcontractors include Summa Technology Inc. of Huntsville, which builds components such as the gas generator, propellant lines,ducts and brackets; Allied Signal Inc. of Tempe, Ariz., and Marotta Scientific Controls Inc. of Montville, N.J., which supply valves; Barber-Nichols Inc., which builds the turbopump; and Thiokol Propulsion, a divison of Cordant Technologies Inc. of Salt Lake City, Utah, which builds the ablative chamber nozzle.
For more information on Fastrac and other Marshall Center activities, contact the Marshall Media Relations Office at (256) 544-0034 or visit Marshall's News Center on the Web at: