A full-engine, hot-fire test of the Fastrac engine was successfully conducted at the Stennis Space Center.
Initial flight testing of the X-34 will take place at Dryden Flight Research Center in Edwards, CA.
|
The X-34's powerplant, the single-stage Fastrac engine, has begun full-scale, hot-fire testing at NASA's Stennis Space Center in Mississippi. The 20-s test demonstrated the operation of the complete engine system. The 60,000-lb thrust engine was designed and developed at the NASA Marshall Space Flight Center in Huntsville, Alabama.
The engine, which is fueled by a mixture of liquid oxygen and kerosene, is started with a hypergolic igniter—a starter fluid that spontaneously ignites when oxygen is fed into the chamber. Once the kerosene is injected, the engine is running. 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—the same cycle used by the Saturn rockets.
Fastrac features a simpler design than previous American-made rocket engines in that it has significantly fewer parts. This is a result of selecting technologies and design concepts that use simple manufacturing and assembly processes. For example casting may be preferred over machining because the latter method could require fabrication in several pieces depending on the shapes of the parts.
Chamber pressure is supplied by a single turbopump, unlike the Space Shuttle main engine, which has four. 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 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. This is simpler and cost less than most rocket engine avionics, which continually modify the amount of propellants flowing into the chamber as changes in thrust are observed by onboard computers.
A typical rocket launch produces a temperature in the range of 5500 °F, hot enough to melt most materials. 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. However, the Fastrac engine design avoids such complex plumbing -- opting instead to cool the chamber by charring and scorching its inside surface as the engine heats, a process called ablative cooling. Layers of silica-phenolic composite material form a liner inside the chamber that decomposes to prevent excessive heat buildup.
Nearly all of the engine's parts are reusable, with the exception being the ablative chamber nozzle and hypergolic ignition cartridge. The chamber nozzle's protective, interior liner is damaged by intense heat inside the chamber and therefore needs to be replaced after each flight. The hypergolic ignition cartridge must be refilled with propellant and replaced after each flight as well.
Development and reliability testing of the Fastrac engine will continue through 1999. The Marshall Center is testing individual components and Stennis Space Center is conducting system-level tests of the full engine.
The X-34 is a Reusable Launch Vehicle (RLV), which will demonstrate technologies that will significantly reduce the cost of access to space. The vehicle is a single-engine rocket with short wings and a small tail surface. It measures 58 ft long and 11.5 ft high (from the fuselage bottom to the top of the tail), with a wingspan of almost 28 ft.
Frank Bokulich
