Pushing the envelope – The phrase is used to describe going beyond known limits, especially in aerospace related activities.

This originates in mathematics; the term envolope describing the area under the line on a graph depicting limits – in this way, anything within the ‘envelope’ is within the limits. The term ‘flight envelope’ was first used in 1944 to describe the area under (or above depending on the orientation) the line on a graph showing limits of aircraft, as affected by various factors (usually, but not always, altitute).