It might be a strange question, but shouldn’t we worry about the rest of the computations being done in the entire route, if this is “much more” than expected?
No, the accounts are good. The problem is the wording of the article:
Much less fuel is needed for track corrections than is expected On its way to its final orbit around the Earth, which will leave fuel for at least ten years.
The word “expected” is a misleading word, chosen by mistake, or whatever you want to call it.
It is simply not possible to calculate the exact amount of fuel required, this calculation is very complicated (see post multikoe for details). So they calculated two things: the mean and the expected deviation (for more information, search for “standard deviation” or “normal distribution”).
The point is, you don’t take in the amount of fuel you’ll need on average; In 50% of cases you will need less, but in the other 50% you will need more…so you have a 50% chance of running out of fuel. What they do is make sure, say, 99% *) Of the cases have sufficient fuel. This leaves 1% where they have a problem (not that the task is completely lost, but they are running out of fuel elsewhere; in other words, they are less than the required 5 years old), and a 99% chance that it is favorable.
*) I have no idea what percentage NASA is actually using, so “99%” is just an example.
That’s why I find the word “expected” embarrassing, which sounds like average. But the point is not that they require less fuel than the “average” scenario, but less than the “everything goes against” scenario. In other words, it was almost certain (you know, “expected”) that they would be left with the fuel: “Less fuel was used than expected…, just as expected.” But this seems very confusing. I would describe it like this: “They had enough fuel on board when everything goes wrong, and not everything goes wrong, so the fuel that was supposed to be a margin of safety can now be used for the mission itself.”
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