Working in Mysterious Ways
People keep asking what the mystery of the Earth-Link is. Me? I say let her stay a mystery. She's done plenty for humanity, so she deserves to remain a secret. But Earth, itself, on the other hand...—Zero on the Earth-Link
The Earth-Link only opens up when a certain type of radiation is emitted from a matter-antimatter engine. This was proven on the maiden voyage of the ISS Deomcies, the first ship to ever use one such engine. This explains why only one Skregg ship has ever made a trip through the Earth-Link; the Skregg are not advanced enough to use more than one matter-antimatter engine.