I recently bought the ALIEN core rule book, and here is a scenario idea I had. It is in rough draft form and still half-baked but I welcome any suggestions and criticisms.
Background: The characters are unemployed contractors offered a huge payout if they take a nine month job to be transported to a refinery located beyond the Outer Rim to get it up and running again. At the end of the nine months, they are to be replaced by a permanent crew of over a hundred workers with heavy machinery, robotic vehicles, and construction equipment to make further repairs and improvements. If the characters accept this assignment, they'll make so much that they'll never have to work again... If the characters ask why they're being paid so much, the answer is there is a labor shortage and the company signed a contract with an interplanetary government which is time sensitive. If the characters ask why the refinery is not currently operational, the answer is that it was owned by a company that was nearly bankrupt from bad investments and was unable to keep in running. It was recently acquired from a company merger, and the new company signed the government contract. The characters happen to have the right skill sets and are nearby and the company can't afford to take no for an answer. The characters could negotiate for more money, but 90% of the payout is at the completion of their contract. To them the job seems easy but tedious... They've done refinery repairs before.
Start: After a period of hypersleep, the characters are dropped off at the refinery which is abandoned and in disrepair. Water drips everywhere. They power it up and get things running again. There is a lot of old automation, some that still works, some that needs repair. A lot of unrefined ore needs processed and prepared for shipping. They split up to do their various tasks, but stay in communication. The lights flicker, and there are power outages. They find some stuck doors, some welded shut.
Once on site and work is underway, things begin to seem fishy as a number of characters find things out independently. A character tries breaching a stuck door using heavy equipment like a mining laser that will cut through anything. Someone gets the refinery A. I. working and it shows concern for all of the workers who were supposed to be emergency evacuated: "Did they make it? How long have I been off-line? Did my warnings make it to the core worlds? I stated that no organics were to be sent here." Another character may discover the acquisition of the refinery was done by a holding company which was a front for Weyland-Yutani.
INSERT ALIENS/MONSTERS HERE (the twist could be that they have nothing to do with the classic Xenomorph alien)
For the Game Mother only: The story behind the story is that the Weyland-Yutani corporation acquired some confidential documents about a possible infestation of alien life forms through industrial espionage, and bought the company owning the refinery to keep it quiet because they do not want another 'Acheron Incident' with colonial marines getting involved and all assets destroyed. The company had the characters hired as guinea pigs with the option of paying them 90% at the completion of their contract. The relief team of over a hundred workers is a sham, and in reality will be company security and scientists.
How it could end: The refinery A.I. may help the characters set the reactor to overload as way to destroy the refinery and everything in it. There is one last escape ship which characters may attempt to board after initiating the reactor overload.