Re: NASA orbit simulation software



Derek Lyons wrote:
It's a very nice real world example, other than the niggling detail of
having exactly nothing to do with the real world and only being
relevant to the nonexistent problem you are handwaving into existence.
Jorge R. Frank wrote:

You might respond that the answer is for NASA to create some kind of "super-sim" that meets all the centers' requirements. But consider that NASA has been doing this work for five decades and most of NASA's sims consist of legacy code going back 3-4 decades, largely coded in languages that don't facilitate modular re-use. At the time they were coded, there was no alternative to this. Each center came to have a workforce with expertise in the particular sims they were using.

Today, there are computer languages that facilitate modular reuse, but the existing sims would have to be completely re-engineered from the ground up in those languages. While this would yield downstream benefits in code maintenance and reusability, the upfront cost of re-engineering the existing sims from the ground up - and then validating them - in order to take advantage of these languages would be colossal. And NASA operates in an annual-budget constrained environment. It is therefore always cheaper to update the legacy code - especially since each center has people who know that legacy code intimately and can update it in a relatively efficient fashion - rather than start over from square one. The only opportunities for making the leap to newer software architectures come at program boundaries, which are fairly infrequent. While JSC would never consider tearing apart its existing shuttle sims so close to the end of the program, they do intend to use JPL's planetary ephemerides in its Constellation sims.

So the various centers have workforces that know their particular software very well indeed.
But like I said, this means that there is a real problem with exchanging data between the centers as the people at the other center aren't going to know how the data was arrived at if it was derived from software that they are unfamiliar with.
Back when the Constellation program first got started, we had someone working on it at NASA contact sci.space.history and ask us where he could find data on the Apollo and Mercury Launch Escape Systems. He wasn't having any luck looking for detailed information on them, as all of the mass of paperwork that NASA generated during those programs was piled away in vast numbers of boxes with almost no indexing.
NASA has a real problem with doing the simple, non-flashy stuff if it cuts even a little way into their budgets for The Big Plan.
For a couple of million dollars all that data could be converted into pdf's and indexed. For a few million more, standardized computer programs could be written for all the space centers that would allow each of them to be able to do any sort of trajectory simulation they desired and be on the same page when it came to exchanging information...but "meat and potatoes" type projects like that don't generate the big headlines that the PAO wants. So even though they would be very useful down the line, they don't get funded - and things go along as they always have, using 50 year old non-standardized trajectory programs while mice nibble away a little more Apollo paperwork by the day.

Pat

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