Don Baker, a writer for a quarterly publication about IRIDIUM asked the following: One question I do have, for all who have been involved, is how the structure of the satellites can be represented via coding in flare-prediction programs. Can Rob or anyone else comment on that, in a way that will be understandable to an audience of non-programmers (including myself)? I thought the answer might be of general interest. The short answer is "No, I can't explain it to non-programmers". It's terribly mathematical and difficult to follow. In fact it is not programming that you need to know, it's mathematics. I just don't see how it can be of interest to your readers. OK, OK, let's give it a shot. o A ray of light skimming a mirror at glancing blow of (say) 1 degree will bounce off at 1 degree. That's just the definition of a reflection. o I know where the observer is with respect to the earth (latitude, longitude and the altitude above sea-level). o I know where the spacecraft is with respect to the earth (from the orbital elements). o I know the attitude of the spacecraft with respect to the earth (because Paul Maley asked the Iridium folks). o I know the orientation of each MMA (Main Mission Antennas, the mirrors) to the spacecraft (from Paul). o I now know the orientation of each MMA to the observer (this is the part that I have to do and it's hard). o Now the question is: The observer is looking at a mirror (MMA), what point in the sky does he see? (A little tricky but basically just the definition of a reflection). o How far is that point from the Sun (just the distance between two points in the sky). Well, that was easier than I thought. Your question implies a belief that somehow there is a little tiny spacecraft in my program. I suppose that's the only way to interpret a statement like "I modeled the spacecraft in software". The only thing that is modeled is the direction in which each MMA is currently pointed. A 'direction' is called a 'vector' in mathematics. So the rest is just the manipulation of vectors which is fairly ordinary mathematics (OK, it's a little advanced). Randy