Measurements of the ion and electron densities associated with the wake of shuttle orbiter were made by the Plasma Diagnostics Package (PDP) during the 1985 Spacelab 2 mission. Cross sections of the wake at distances of 50--250 m downstream and measurements along the wake axis from 5 to 100 m were obtained. The POLAR wake model, developed for The Air Force Geophysics Laboratory to study charging of spacecraft in low-altitude high-inclination orbits, was used to perform a three-dimensional simulation of the plasma wake evaluated at points along relative trajectory of the PDP. The POLAR code uses several simplifying assumptions to predict wake densities. These include neglecting the magnetic field and assuming that the plasma is quasi-neutral. The code models plasma density ahead of the expansion front, using a neutral approximation, and models the plasma density behind the expansion front by using the self-similar solution of the expansion of a plasma into a vacuum. For cases where Ti≈Tc, the front is not sharp and thermal motion can account for most of the expansion. This approach is computationally very efficient. The results presented here are the first known comparison between such a model and actual in situ data obtained for objects of scale size ≈104 &lgr;d. Excellent qualitative and quantitative agreement are found at distances greater than ≈30 m, indicating that at least to first order, the model's approximations are justified. An intriguing disparity between the model and data suggests that the orbiter's near wake may be filled predominantly by a pick-up ion population created from neutral contaminants and that these would have to be included if accurate wake models of large gas-emitting objects are required. ¿ American Geophysical Union 1989