But to fly so low as to slow the ship down if unpowered, they'd generate enormous heat from atmospheric friction. They could use shields but then the ship would

But to fly so low as to slow the ship down if unpowered, they'd generate enormous heat from atmospheric friction. They could use shields but then the ship would glow, alerting the natives below and violating the Prime Directive. And they called it "standard orbit". Orbiting doesn't require power. Even a satellite in a very low orbit only needs a slight boost once in a while to counter the drag.