The parameter space of n ordered points in a projective d-space that lie on a rational normal curve admits a natural compactification, which is a projective variety. A seemingly elementary question, asked independently by both Speyer and Sturmfels is: what are the defining equations? In this talk, I will explain the motivation, a complete result for d = 2, a partial result for d = 3, the challenges involved for larger dimension. This is joint work with A. Caminata, N. Giansiracusa, and L. Schaffler.