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we often take the things we use everyday

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for granted we use them and we expect

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them to work that's because they were

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tested many many times before we even

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see them would you ride in a car that

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had only been tested once puffy wouldn't

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work so well how about a toaster not so

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good either

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now what about a satellite the same

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thing applies what if we had a telescope

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that couldn't take pictures luckily NASA

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was able to put glasses on Hubble but

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it's not always so easy

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that's why engineers do their best to

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make sure things work right and we'll

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keep working for a long time and how do

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you design something that can do the

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same thing over then over and over again

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you test it before we start testing

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though we should make sure we know a

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little bit about our mission that way we

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can figure out what we're testing as

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well as what we're allowed to do to

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improve it these are called constraints

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constraints help engineers get a good

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idea of where to start for example we

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probably wouldn't want to build a lunar

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lander out of let's say bricks

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actually let's use that example we need

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to land humans on the moon we have a

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design for a lunar lander and it has to

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land safely from the same height each

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time we also have to be able to reuse it

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so let's try it out

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well that didn't work

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good thing we're just testing let's try

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it again but let's think about how we

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clothes but how can we keep it from

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tipping over at all maybe some rockets

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great now maybe you were wondering what

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the letter n was doing up in the corner

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but simply N is a variable scientists

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and engineers use this variable to

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represent the number of times we've

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tested something in our example we've

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tested our design three times so N

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equals three luckily we came up with a

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good solution some designs need to be

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tested hundreds of times before they

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work but that's okay in the end all this