# Why did NASA launch a spacecraft into an asteroid?

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I’m sure they did this whole thing on paper before executing, but why did they need to actually do it?

Normally, I’m all for funding space agencies, but there doesn’t seem like a whole lot of value in doing this. If you know all of variables in concept, you should be able predict that it would work. Right?

In: 0

Just to make sure it worked the same way the math said it should.

You never know for sure until you actually try it.

Also flashy tests help with funding.

It was to test if they could redirect asteroids that would certainly impact Earth. It was just a hypothesis until they tested it 🙂

I’m not sure you can say with confidence you can hit a small object with a satellite traveling at 12,000km/hr until you actually do it.

I think it makes sense to do a trial run before we have to take our real shot at an incoming asteroid that’s going to take us out. We’ve clocked asteroids going through our solar system at over 100,000km/hr! When a real threat is coming at us we may only get one shot at deflecting it.

We know that our impactor has a certain momentum. How much of that momentum will be transferred to the asteroid we’re impacting? Will the asteroid break up when hit? How much debris will be thrown off, and in which directions? How closely will all that match our on-paper modelling?

In addition to this: space is hard. Doing something for the first time is also hard. If we ever actually *need* to impact a space rock to redirect it, we might need to do so in a rush. Having a working, tested plan will make it easier, faster, and more likely to succeed.

Earth doesn’t like asteroids

Asteroids like earth

Qe wanna use spacecraft to redirect in case one sneaks up on us

> you should be able predict that it would work. Right?

Sure. But… if there is a giant asteroid about hit Earth we probably want to be really sure that it works. Like not just ”we ran the numbers” sure but actually have done it sure. There is also a lot of practical experience that doing this achieves. Building a spacecraft in theory doesn’t allow you to find and solve all the problems you run into when really doing it.

Bear with me for this example:

In theory, the material of brake disc and pads does expand when hot.

In practice some brakes need to be measured when cold as measuring it hot will read them as too thin. Go figure.

So basically, you can’t be sure to have predicted every variable. A practice test should prove you understood how to correctly apply a sound theory. You may get the theory right and completely miss how it applies.

It was less about figuring out if they could hit the asteroid and more to see what would happen to it afterwards.

It is hard to model such an impact when you don’t know exactly what these rocks are made of and how they will behave if you crash an object into one.

The idea is to crash the probe into the asteroid and then to observe it over a period of weeks and months to see how much its orbit changed.

The obvious benefit of that is that if we ever actually need to divert an asteroid from hitting earth, we will have a better idea about how hard we will have to hit it.