Linear Hyperdrive
From ROI Wiki
A Linear Hyperdrive is an advanced hyperdrive technology that gets its name from the method in which it operates. Namely, the drive's power curve increases linearly, and is only limited in top speed by how much energy you can push through the system, or how much plasma pressure that the nacelles can withstand. The top end speed of a linear hyperdrive has not yet been discovered, even though it has already been proven to be able to cross vast distances in a matter of days or hours that would take a comparable warp drive powered vessel months or even years to cover the same distance.