ELi5 How does a rocket not fly away when testing thrust?

Question

I see the thrust of rocket engines, and things like vector engines, being tested a lot at the moment with all the Space X stuff happening. How come these rockets that are testing their thrust don’t actually lift off? They don’t appear to be held down so well as to not let the thrust overpower it.

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Answer 1

For short tests, the rockets are nearly full of fuel and the thrust of the engines is mostly balanced out by the weight of the stage. A rocket would typically have a thrust/weight ratio of about 1.2.

For long full duration tests, the standard hold-downs aren’t strong enough. [SpaceX uses cables that attach to the top of the stage.](https://www.nasaspaceflight.com/wp-content/uploads/2018/02/Block5.jpg)