AnimationTime and motionTrailLength not completing based on the given array path

I am able to create a comet that moves based on the (x,y) points in an array. While moving it leaves a trail to give the comet like effect.

My problem is that, I have to set my var motionTrailLength with a big value, (=200) and my var animationTime to (=3000), so the trail does not disappear halfway. I am attempting to shorten the var motionTrailLength to 20 and var animationTime to 1000.

The comet should move through the defined array point withouts breaking halfway. I do not have an idea why this happens and I have check the code many times. I think my logic is wrong, so I need your help.

Can someone please help check the code here and help me know whats wrong? Appreciate it very much.