It is shown by means of numerical simulations that an injection of a tenuous suprathermal electron beam into a fully ionized plasma from spacecraft can lead to an excitation of ion acoustic waves. The return current carried by the ambient electrons has a drift speed that is much slower than the beam speed, so that these electrons can excite the ion waves via wave-particle interaction. Numerical simulations confirm the excitation of ion acoustic waves and the acceleration of ions near the spacecraft producing a high-energy tail. ¿ American Geophysical Union 1988