Gaps in a ship's protective shields that are needed for propulsion and weapons.[1]
[1] Except destructive shields like the Union TransDim shields. which can be made - mono directional transparent and even selective (the latest version could be made transparent to sound. (An invention by Circuit and SHIP)*
*When Captain Olafson asked SHIP to make the shields transparent to sound, Captain Olafson asked something completly impossible until that time. SHIP using the Narth Interface came up with a algorithm for the shield projectors to generate a shield barrier transparent to sound waves.
Circuit used this to create the TD Shield transparency adjuster. Giving credit to SHIP, Mr.Warner and Two-Three in the development. Making it possible to operate thrusters and weapons under shields without the need to create gaps.