Linux Use Rocketing at Jet Propulsion Laboratories

Breckheimer has benchmarked a number of computers since 1984, using a program called nbodyf. This program takes an initial vector and integrates it with the equations of motion for all planets in the solar system over a five-year period. In 1984, a DEC VAX 11/780 took an hour and a half to run the program. Now an HP J5000 can do the same thing in under three seconds. While speed is important, the computer system must also get the correct result. Therefore, the answer is tested using a subset of INSS containing about 1 million lines of code. When run on the benchmark tests, the $2500 PC running Linux compared very favorably with results obtained on an HP 755 which cost over $30K. Linux Red Hat version 5.0/5.1 was installed on a generic 200MHz PC with 64MB RAM. It ran the nbodyf program in 14.5 seconds, versus 13.3 seconds for an HP 755/125 running HP-UX 9.07, and beat the times for the HP J21, HP C110 and HP 755/99. On the other tests, it ran as well or better than the 755/125. Later tests were run using a 450MHz PC, and its performance improved roughly in proportion to clock speed. “An additional side benefit we observed was a slight improvement in accuracy,” says Breckheimer. “The Fortran 77 compiler, obtained from Absoft, utilizes 80-bit registers for some of the built-in functions used by our navigation software. On all previously tested UNIX platforms, we were limited to 64-bit arithmetic, so the Linux version of Absoft Fortran 77 offered some definite improvement.”

Year after year, Linux is gaining greater acceptance within NASA. Given the huge investment that exists in older systems, it is not likely that Linux will replace Windows or UNIX in the short term, but Linux is working well where it has been used. “Having Linux's desktop functionality tremendously improves the engineers' efficiency and speed,” says Rodriquez. “Projects greatly benefit when engineers have readily available desktop analysis tools.” His one complaint, however, was the limited amount of peripheral hardware that Linux supports. But with so many computer vendors now offering Linux and the increasing number of Linux applications, this situation is rapidly changing. Breckheimer, who has been working with INSS through several platform incarnations, feels that Linux “opens up a significantly cheaper path to future computing for many of the projects we support. While HP, Sun and SGI workstations dominate our operations environment, Linux-based PCs may make a significant impact soon. As more projects accept Linux, computer costs for navigation systems will continue to decrease significantly.” So, while you don't have to be a rocket scientist to appreciate the advantages of Linux, these days even rocket scientists are beginning to adopt it as an alternative to Windows.