Re: NASA orbit simulation software



Greg D. Moore (Strider) wrote:

Umm, no. If they are using hte same software and put in the same inputs, they'd see the same outputs.

Ah, but that's where the fun comes in...each center has to figure out those inputs on its own. That's how you find errors in the input data.

Software is very deterministic that way. If they DO see something different, it's a hardware issue, not a software issue.

If you really want to test the answer, you calculate it two DIFFERENT ways.

Yeah, but Jorge seemed to imply that each center had "its" favored program and wasn't going to use the one used by the other center(s).
So if you end up with two different outcomes from two different programs, then you know something is obviously wrong, but what exactly and in which program run? Was it a faulty input of information or did the program deal with those particular inputs in a way that led to a incorrect answer?
That's where the real mess would start, as center "a" doesn't have much experience with the program center "b" is using and vice-versa.

But having different space centers using different programs to try to figure out the same thing is bound to cause communications problems if one program comes up with a different solution than the others, and they want to figure out _why_ that occurred.

You're assuming that they are trying to figure out the same thing. (which given NASA is a bureaucracy may be true, but is not generaly the goal).

It might be a very good idea to have them try to figure out the same thing, and see if their answers agree.
Extra math work is pretty cheap compared to the cost of a spacecraft and its booster.
A real-world example of this occurred in the Soviet space program.
The math whiz-kids back in Moscow would send the specs to Baikonur of what launch trajectory a booster was to use and what propellant load was needed for it to put its payload into the desired orbit.
As one launch approached, one of Korolev's assistants looked at the incoming figures on the amount of propellant to be loaded on a specific launch, and they didn't look right to him based on past experience with other launches and the weight of the payload that would be carried. The payload would not reach orbit due to too little propellants being carried.
He ran through the math several times and still kept coming up with a different answer than what Moscow was telling them, so finally went to The Chief Designer and told him there was a problem.
Korolev asked him if he was _completly sure_ a mistake had been made, as one didn't question orders without a very good reason, and this could mean delaying the launch.
The assistant stuck to his guns, and Korolev called Moscow and demanded that they double-check their math, although headquarters was not used to being talked back to.
The assistant felt like his head was on the chopping block as first one and then another hour passed with no return call from headquarters. Finally, a call came in... there had indeed been a "small" error in the amount of propellants to be loaded and new figures were sent to Korolev...which agreed exactly with those the assistant had found with his math work.
Not only was the launch now saved by the assistant's hunch and boldness in bringing it to Korolev's attention, but The Chief Designer now had something to rub Moscow's nose in if they ever gave him trouble about planning a mission.
The assistant got his own private dacha out of that incident.
Having two separate teams figure out the same information in two different ways via original information inputs that they themselves had to determine would be a great idea; but each team should be completly conversant with the method the other team is using so they can quickly find the problem if the two end results differ significantly.

Pat

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