It calculates the `uncomputable'. New NASA supercomputer system can analyze complex processes

THE National Aeronautics and Space Administration (NASA) yesterday dedicated a unique supercomputer system that will help scientists and engineers calculate the seemingly uncomputable. They may be able to find out what happens when galaxies collide, watch the air pour around an aircraft without actually building it, and study the turbulence inside a storm as it roars across the Great Plains. NASA's Ames Research Center here has cranked up its numerical aerodynamic simulation (NAS) facility, a system that NASA believes could have direct ramifications on our lives. It also may help the United States keep ahead in the two technologies it still dominates: computers and aerospace.

While dozens of supercomputers exist on university campuses and in corporate computing centers, NAS is unique because it is a system, a symbiotic electronic community centering around a supercomputer with the whole far more powerful than the sum of its parts, according to Ron Bailey, chief of the NAS Systems Division. The system is capable of showing what happens in extremely complex and chaotic processes over a period of time in three dimensions, in full animation, and in color, the stuff that computer scientists' dreams are made of.

To an engineer, flowing air acts like a fluid in motion, so the study of the air stream over a plane's wing is a study in fluid dynamics. So, too, is the flow of water around a submarine hull, the dynamics of a storm, and the turbulence of gases inside an engine. These problems may not sound complicated; indeed, the equation used to solve them is based on the simplest and most basic equation in physics, yet they have been virtually uncomputable until now.

``In essence, the equation we're solving is F = ma [force equals mass times acceleration],'' says Paul Kutler, chief of the Fluid Dynamics Division at NASA. ``That's Newton's Third Law. But when you expand those terms to make them applicable to viscous fluids, those equations get very, very complicated.''

In the case of studying the airflow around a wing, the computer might break down everything that happens into millions of discrete points on a three-dimensional grid. Then it might call up five differential equations to determine the air pressure, density, and velocity in all three dimensions every fraction of a second for every point on the grid, a staggering amount of numbers.

``That's why you need a supercomputer,'' Dr. Kutler says.

The supercomputer at the core of NAS is a Cray 2, arguably the world's fastest computer. The Cray, which has four processors instead of the usual one, can hit a speed described as ``two gigaflops,'' meaning 2 billion floating-point calculations each second, although it tests at only 1.7 gigaflops doing NASA's typical calculations. The internal memory can contain every word in every book in the library of a medium-sized city, 268.4 million words, according to Dr. Bailey.

Surrounding the Cray are two Amdahl 5840 mainframes, adding computer power and a place to store much of the data. In addition, NAS has four Digital Equipment Corporation VAX 11780s, which provide even more power and handle the communications between the computers and the people using them. There are 38 high-powered engineering work stations and more than 200 disk drives. Researchers also can call in from personal computers by telephone, Bailey says.

All the computers use the same operating system (UNIX), the basic commands that run the machines. Bailey says this enables the researchers to use any of the computers without having to learn a new command language. When NASA adds another supercomputer in 1988, it can be plugged into the system easily. Everything is connected to everything else; the software is off-the-shelf.

Researchers at 27 locations around the country, including other NASA facilities, universities, and every major aerospace company, are now plugged into NAS.

Kutler says NAS will solve problems that simply cannot be solved any other way. The proposed aerospace plane, which could reach orbital altitudes and cut flying time across the Pacific by more than half, cannot be tested in a wind tunnel, and scale models are no help.

NAS already has been used to study the flow of water around submarine torpedo tube doors and the internal workings of the space shuttle's main liquid-fueled engines. As a result of the Challenger accident, NAS is studying the dynamics of aborting shuttle missions just as the shuttle separates from the boosters and the fuel tank right after launch - four separate vehicles flying apart simultaneously, one of which carries humans. NAS also is working on making helicopter blades more efficient.

``It is interesting to note that the US has a favorable trade balance in only two areas: aerospace and computers,'' Bailey says. In both cases, the US is being challenged by the Japanese in computers and by the Europeans in aerospace. ``Here we have a program in which one can help the other and vice versa.''