for me, and Ridley (it was mentioned at the time), the reason for making Prometheus was to explain that original SPACE JOCKEY (you know, that one that Giger designed and everyone forgot to ask him about),
To be quite frank, I was expecting something BIOMECHANICAL like this; space worm:
Scene 1: deep space. This off-white space worm pull and stretches itself through space using its own spasming centre of gravity.
Scene 2: track to a view INSIDE this worm. We see platelet-like 'red blood cells' and tendrily 'white blood cells', close in one one of them. We see that this red blood cell has a black iris in the middle of it, a sphincter of black goo. The outer casing of the cell splits, the 'doughnut' shearing into two crescents, each containing a percentage of this black goo. The white blood cells in the worm recognise this act and attacks. One white blood cell sinks half its tendrils into one crescent. Another white blood cell digs half of its tendrils into the other.
Scene 3: the upper crescent (with its tendrily attacker sticking out of the top of it) straightens out, becoming the turret. This straightened out turret rolls over so that its attached tendrils reach forward and grip the lower crescent; the upper tube pulls the lower crescent towards it. The surface starts to undulate as the elephantine Space Jockey begins to be defined, spawned by the black goo within. The turret also begins to be defined.
Scene 4: The proto-Space Jockey embeds itself into the inside wall of the wormlike thing, those tendrils that remain free align themselves along the side of the Space Jockey. As the detail of the Space Jockey resolves, the inner surface of the worm starts to change also, taking on the familiar Giger-ribs look. The remaining 'blood cells' pop into a green sparkly soup, filling the void.
Scene 5: external view of the worm as its surface changes from off-white to giger-ised embossed, curving and swelling into the classic derelict shape. A shadow looms across it from the Engineer UFO. Space Jockey ORRERY rings pour out of the derelict, actually further out than the map rings in Prometheus and, when they disappear, it takes the whole derelict-Juggernaut with it - transdimensionally.
Notice that on the THE EVOLUTION box art I used to illustrate this sphincter-ish meander, they've white-washed the original (elephantine) Space Jockey over whatever it became in Prometheus, some back-engineered suit for a stunted giant. I wanted to see how THE ORIGINAL space jockey came about. I wanted to see why the EGG CARGO. Alas, and alak.