Help with setInterval

is there any reason why my function is being called instantly and not after the set milliseconds?

var rocketintervalID:Number=0;
onMouseDown = function () {
if (shots > 0 && canshoot) {
shots–;
canshoot = false;
shotsheard = true;
s_rocket.start(0, 1);
rocketintervalID = setInterval(exploderocket(), 1500);
}
}

function exploderocket(){
insert explosion animation here
clearInterval(rocketintervalID);
}

this is just a piece of my code.when someone clicks the mouse i want it to fire then rocket, then after a set about of time it makes an explosion. the explosion is happening instantly, at the same time as the rocket sound. tried setting the interval to like 100000 with no change. what am i doing wrong?