Fill in the blanks with the correct form of the verbs.

1. After (check) all systems, the computer begins the countdown.
2. As soon as the countdown (end) , the rocked is launched. 
3. When the computer (activate) the abort engine, the LAS is ejected. 
4. After (fire) for 3 seconds, the abort engine burns out.
5. Once the crew capsule (separate) from the LAS, the parachutes open.
6. After (open) , the parachutes lower the capsule gently into the sea.