Alien: Ridley's Criteria for the Derelict

From

The Derelict

Ridley was probably talking about George Adamski's photographs of flying saucers such as the 
Venusian Scoutship that were taken in the early 1950s

When Ridley joined the project, Chris Voss's lobster derelict had been the design that O'Bannon wanted, however it didn't satisfy Ridley and he then went through a number of different ideas for the ancient derelict ship before he settled on the concept that finally interested him that we see in the final movie. 

1. Fantastic Films: "What are the criterian for credibility in the design of alien spacecraft?"
   Ridley Scott : "I have come to accept a wide variety of possibilities. And strangely enough, the more mundane something is, the more it can sometimes stagger people. Simplicity can be more powerful than you think. Take a UFO for example. How do you design it so people believe it? One of the best UFO shots is one from the thirties with the portholes. It looks like an inverted plate with a sort of cap on it . And oddly enough it's rather archaic, it appeals to me as a solution, rather than an incredibly refined, sleek spacecraft. I like the idea of a spaceship where you've got no idea what kind of energy drives it and you've never seen anything quite like it before. "
   
   
   
   Fantastic Films: "Like Giger's instead of the Foss conceptions?"
   
   Ridley Scott : "Foss' ideas were interesting but they tended to all look alike. Giger's craft was definitely not of this world"  (Fantastic Films (UK)# 3, (US) No.12, p27) 

black and white image of Foss' derelict from Skeleton Crew August, 1990