TweenMax timeScale issue

ok so i have an object that tweens 700 pixels across the screen with TweenMax, at any given moment, i would like to have the ability to slow that objects speed down by half speed, but also have to ability to resume it to the regular speed,

right now i use this

TweenMax.to(ship,3{y:700,timeScale:1,overwrite:true,onComplete:removeTween,onCompleteParams:[ship]})

to slow the ship down, i apply the same tween over the object but with timeScale set to .5, i know this is doomed for failure, is there some way to alter just the timeScale variable only rather apply a new tween?