Stunnel

A stunnel was a portmanteau of Stellar Tunnel, an interstitial connection which could be used for interplanetary or interstellar transport.

When the Daleks attacked Pluto's moon, Charon, a group of human scientists there tried to use a stunnel to escape. (PROSE: GodEngine)

The Interstitial Mass Transit System planned to create a stunnel to connect Mars with Arcturus. (PROSE: Transit)