David Simpson

I am a scientist (a physicist) who works with one of the on-board computers of the Hubble Space Telescope. This computer (called the DF-224) rotates the Telescope to point to the objects that the astronomers want to observe, then keeps it steady while the observations are being made.

To keep the Telescope steady, the DF-224 computer reads in data from several different sensors that tell it how far the Telescope is pointed from where it should be. It then performs a long series of calculations to find how to best rotate the telescope to keep it steadily pointed on target, and finally sends the commands to perform the tiny rotations that keep the telescope steady. This whole set of calculations is done 40 times each second, and can keep the telescope pointed at its target with an accuracy of about two millionths of a degree.

The DF-224 computer is about 20 years old and is barely able to perform all the necessary calculations quickly enough. Right now we're very busy trying to re-write its software so it will run on a newer computer that will replace the DF-224 and be installed by astronauts on the Space Shuttle in 1999. It will be a lot of work to get the software done by then, but it's just the kind of challenge I've always enjoyed.

I have wanted to be a scientist all my life. As a boy, I was always reading science books, experimenting with my telescope, microscope, and chemistry set, building radios and model rockets, collecting rocks and fossils, and so forth. I kept a notebook of my science experiments and of fun math problems I had worked, and I taught myself calculus from a library book because I couldn't wait for them to teach it in school.

I remember once in seventh grade when our math teacher asked us to make a poster showing the prime numbers between 1 and 100. I thought a poster would be too boring, so instead I built a simple computer out of a wooden board, batteries, wire, a small light bulb, and a nail. The wood had a hole for each number from 1 to 100, and I wired it so that the light bulb would light up if you put the nail in a hole that corresponded to a prime number. I was always trying to find ways to make things more interesting and fun.

I have always believed that learning is a lifelong process, and I have been going to school for practically my whole life -- 30 years now! After high school, I went to get my bachelor's degree in physics at the Virginia Polytechnic Institute and State University, then master's degrees in physics and mathematics at the Johns Hopkins University. I'm now about half-way through my Ph.D. in physics at the University of Maryland, and I plan to get at least two more degrees when I finish that. I'm always wanting to learn new things -- not just physics and math, but also things like Latin, cooking, history, music, skiing, and ballroom dancing.

What I like best about my job on the Space Telescope is the people I get to work with. There are a great many technical challenges with this job, and each person in our group contributes his or her own special set of talents and skills. The people who work here are the most talented that I've ever gotten to work with -- and they're a lot of fun to work with too!

You can learn more about the on-board computers for the Hubble Space Telescope and other NASA spacecraft by checking out our group's Flight Software Systems Branch Web page.

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