Understanding the magnetic exchange coupling and fundamental Hamiltonian of the parent compound of FeAs-based superconductors is extremely important, because such information will lay the foundation from which superconductivity induced changes can be investigated. For example, it is well known that spin waves in the parent compound of cuprates can be described very well by local moment Heisenberg Hamiltonian. Since the parent compound of FeAs-based superconductors are semimetals, much has been debated about the microscopic origin of the magnetism in these materials. We propose an experiment on MAPS focused on measuring the low temperature spin-wave dispersion in the HHL zone of the non-superconducting parent BaFe2As2. Such a study will also probe the lattice effect on magnetic exchange couplings along the c-axis.