We investigate the accuracy attainable by forthcoming space-based observations of the cosmic microwave background (CMB) temperature and polarization anisotropy in constraining the dark energy density parameter ΩQ and equation of state wQ = pQ/ρQ. Despite degeneracies among parameters, it is possible for high-precision observations such as those from the Wilkinson Microwave Anisotropy Probe and Planck to provide interesting information on the nature of the dark energy. Furthermore, we show that imposing a flat universe constraint makes it possible to obtain tight limits in the space of dark energy parameters even from the CMB alone.
