Specifically the sounds he gets on songs like "High Landrons," "Venus Reprise," and "A Change Has Come to Me?"
He used an MXR rackmount flanger for the first two, and later a Toadworks Barracuda Flanger.
I've tried a few in the Helix, but haven't been able to dial in that "spaceship swooshing across the sky" that he gets - almost like a doppler effect.
Any suggestions, and what settings?