The scientific and technological needs of the U.S. Department of Energy posed by the Accelerated Strategic Computing Initiative/Academic Strategic Alliances Program (ASCI/ASAP) encouraged the University of Illinois at Urbana-Champaign (UIUC) to establish the Center for Simulation of Advanced Rockets (CSAR) in September 1997.
The goal of CSAR is the detailed, whole-system simulation of solid propellant rockets from first principles under both normal and abnormal operating conditions. The design of solid propellant rockets is a sophisticated technological problem requiring expertise in diverse subdisciplines. These subdisciplines include the ignition and combustion of composite energetic materials; the solid mechanics of the propellant, case, insulation, and nozzle; the fluid dynamics of the interior flow and exhaust plume; the aging and damage of components; and the analysis of various potential failure modes. These problems are characterized by very high energy densities, extremely diverse length and time scales, complex interfaces, and reactive, turbulent, and multiphase flows.
The primary target of CSAR is the reusable solid rocket motor (RSRM) of the NASA Space Transportation Systems, better known as the Space Shuttle. The basic components of the Space Shuttle include the solid rocket boosters, the external liquid fuel tank, and the orbiter.
The solid rocket boosters (SRBs) are the largest solid-propellant motors ever to be flown and the first to be designed for reuse. Their total length is 149.16 feet (45.46 meters) and they have a diameter of 12.16 feet (3.71 meters).
At launch each motor weighs around 1,255,415 pounds. The solid propellant makes up about 1,106,140 pounds, or around 88 percent, of the motors total weight. Prior to launch the SRBs carry the entire weight of the external tank and orbiter, the whole system weighs about 4.5 million pounds. Each SRB has a thrust of around 3,000,000 pounds at launch, providing 71.4 percent of thrust at lift-off. Before the SRBs separate from the external tank they accelerate the shuttle to approximately 3,100 mph and take it up to an altitude of around 150,000 feet (28 miles).
The picture to the right shows just some of the SRB's different components.
Shown here is a diagram of the SRB (taken from the Thiokol data book) and a schematic of a small region on the combustion surface.
The propellant in a typical SRM consists of a high density packing of ammonium perchlorate (AP) particles, which act as the oxidizer and can burn alone if ignited at pressures above 20 atm, embedded in a rubber fuel binder (PBAN or HTPB). Aluminum (Al) particles are also added, which burn in the gas-phase products of the AP-binder combustion. Aluminum, as an additive, is used to increase the chamber temperature and dampen chamber acoustics.
Typical composition of a propellant is 70% by weight AP, 16% by weight Al, and 14% by weight binder. Burning of the propellant takes place within 10 to 50 microns of the surface at high chamber pressure.
A picture of a bimodal (200 micron/5 micron) heterogeneous solid propellant (from Hickman and Brewster). The left picture shows the distribution of the 200 micron AP particles. The right picture is a close-up, showing the distribution of the 5 micron AP particles.
The sheer size of the solid rocket booster is what presents a problem. The SRB is measured in meters while the combustion layer being studied is measured in microns; it takes one million microns to equal one meter. Because of this vast difference in length scales, the development of a single integrated numerical code to cover the entire range of length scales is prohibitively expensive, and a sub-grid combustion model had to be developed. Rocfire is exactly that, a three-dimensional unsteady simulation of composite propellants. The process involves many complicated mathematical and scientific procedures, and some of them are discussed in more detail in later sections.
For more information regarding the SRBs and the other components of the Space Shuttle check out these Web sites:
NASA Spaceflight Webpage: Relevant information about spaceflight, including SRMs.
The Space Shuttle Clickable Map: Images and details of the Space Shuttle apparatus.
Space Shuttle News Referense Manual ~ SRB: Detailed information on the SRBs and other numerous aspects of the entire Space Shuttle.
The Space Transporation System: Images and details of the Space Shuttle apparatus.
Thiokol Propulsion: Description from the developers and makers of the SRBs.
T.L. Jackson (webmaster)
E-mail: tlj@csar.uiuc.edu
URL: www.csar.uiuc.edu/~tlj
Site Last Modified: February 1, 2003