Following a long kosmiche phase, Tangerine Dream finds a new theme in the mid-70s: “Rubycon,” “3 AM at the Border of the Marsh from Okefenokee,” “Invisible Limits,” and this track. Everything depends on a reading of borders and limits. The border, whether Julius Caesar’s, Georgia’s, or NASA/Apollo’s, is a place of “fear” and trembling (a menacing e-minor dominates “Stratosfear,” for example, which finds the band hurtling toward guitar-based, Pink Floyd territory). One cannot simply overcome the border, or wish it away, in part because it’s the living end.