1. Briefing might need to be redone. It seems a bit "unofficial"
2. Loadout: change the numbers of ships & weapons available.
3. Set a background for the mission
4. libra2pop is useless. Its set to "true" so it always happens, and you could simply put it in the ship information, rather than as an event.
5. Same with the libra1 one (0:04 is most of the times before the player gets the in-game screen). If you want to simulate an ongoing battle, just change it individually for each ship in the ship info boxes.
6. If you want Beta 1 to be unable to die in the mission, add a ship-guardian before the "set-invulnerable". Only this way, you can prevent having it killed by a "single hit", taking down its 100% with one hit.
7. More messages and a RTB message/directive (you'll need another chained event for that) would be nice.
Else than that, good work. The structure is clean and simple, there's little or no typoes or grammar problems, and the events seem to work as they should and are linked in an useful way.