How to create trail for sky rocket/spaceship

Hi.

I´m working on an asteroid game and don´t get it to create a nice trail for my spaceship(s).
It doesn´t need to look spectacular, just “nice”.

I tried a comic look alike version with angled mc´s, whose scale are tweened down and up. But it´s not the right look.
And I tried some flame effects by as3, but it not seems to be a smart solution. Nice look, but needs a lot of memory space.
Maybe someone got a inspiration, I don´t need a solution.
Thanks.