Ripley lets out a scream and strikes the button that opens the airlock door, instantly de-pressurising the cabin.

 

The alien is blown towards the door.....

 

but manages to get a grip on the edges.

 

Ripley readies the harpoon gun.

 
The alien starts to pull itself back inside....

 
as Ripley fires.

 
a direct hit, the alien loses it's grip on the door.....

 
and is thrown out into space.

 
the airlock door closes and traps the harpoon weapon in it.

 
It uses the cable as a tether to reel itself back to the ship.

 
Ripley wonders what it's going to do.

 
It tries to gain access back in the craft through one of the rocket engines.

 
She decisively hammers the button that fires the engines.

 
The alien is blasted by the rockets and cannot hold on.

 
Ripley watches as the evil creature is....

 
blown into space.

 
The main engines burn  

 
Finally, it's gone.

 
She makes a last log recording. "Final report of the commercial starship Nostromo.  Third officer reporting.  The other members of the crew, Kane, Lambert, Parker, Brett, Ash and Captain Dallas are dead, cargo and ship destroyed.  I should reach the frontier in about six weeks, with a little luck the network will pick me up.  This is Ripley, last survivor of the Nostromo, Signing off."

 
She says "Come on cat" to Jones....

 
Then they both go to sleep.

 
The end.