My childhood dreams

When I was a child  used to dream of being an astronaut. I've always been fascinated by rockets, their slow lift off is really amazing; they are quiet, then all of a sudden they start their noisy and huge fight against gravity!
As many incidents teach us, that's not an easy fight, but/however (pick one, they both mean the same thing) most times they win!
But One day I'd built a model rocket but when it was lifting off, it exploded!
In that moment I realized that an astronaut could have been a very dangerous job, so I switched my interest to engineering!
In a nutshell, I would have wanted to be an astronaut, then I realized that sending someone else into space is safer!

Good effort! Just remember to use punctuation (commas ',') where you need to, and learn some more on grammar and connectives: 'but' and 'however' mean the same thing but use just one. 

Well done! ^^

My childhood dreams

When I was child used to dream to be an astronautt. I've always been fascinated by rockets. Their slow lift off is really amazing. They are quiet; then all in a of the sudden they start their noisy and huge fight against gravity!
As many incidents teach us, that's not a easy fight, * but however * most of times (or:  most of the time)they win! 

But one day I'd built a model rocket but when it was lifting off, and it exploded!
In that moment I realized that to be an astronaut could have been a very dangerous job, so I switched my interest to engineering!
In a nutshell I would have wanted been to be an astronaut then I realized that sending someone else in the Space it's is safer!

* Use "but" or "however", not both

, but most of the time...

; however, most of the time...

Good job!