Question: How fast do you want the year to go backwards? Do you want the timer to stop at 1900? When do you want the satellites to disappear?

If it is a very fast countdown, you can have a dynamic textbox on the stage, and use code to update the text inside the box.

1) Create a Dynamic text box on the Tablet
2) Turn the TextBox into a MovieClip
3) Create a variable for the Year
4) Write a function that will be called by an ENTER_FRAME
5) Add event listener to your TextBox

1) Create a text box and make sure the type is Dynamic. Give your text box an instance name "yearTxt" Be sure to choose a font and embed the numbers.
2) Select your text box and convert it to a MovieClip using F8 on keyboard. Be sure to give your MovieClip and instance name "yearMc"
3) In your actions layer, write the following code:
Code:
var theYear:int =2013;

function countDown(e:Event):void{
	yearMc.yearTxt.text=theYear;
	
	if(theYear==1969){
		//put code here to kill your satellites
		satellite1.alpha = 0;
		satellite2.alpha = 0;
	}
	if(theYear==1900){
		yearMc.removeEventListener(Event.ENTER_FRAME, countDown);
	}
	theYear--;
}

yearMc.addEventListener(Event.ENTER_FRAME, countDown);
Hope this helps!