To shorten the distance from 85 light years to 20 light years, the starship Enterprise must travel at a significant fraction of the speed of light. The relevant formula for this calculation is l = l0√(1 - (v/c)²), where l is the contracted length, l0 is the proper length, v is the velocity, and c is the speed of light. By applying this formula, one can solve for the required speed (v) to achieve the desired distance contraction. This question highlights the fascinating implications of relativity in space travel. Understanding these calculations is essential for theoretical discussions on interstellar travel.