We study an electromagnetic environment around a spacecraft in the solar wind plasma, where the Debye length &lgr;D is much larger than the scale size of the spacecraft Ro. We perform computer experiments using a two-dimensional electromagnetic particle code (KEMPO) with a half open boundary model whose internal boundary corresponds to the spacecraft. We show formation of an ion acoustic shock around the spacecraft and clarify its parametric dependence on the background plasma parameters. Scale size of the shock is about 3~4&lgr;D. The shock formation is observed when the solar wind proton temperature is lower than the electron temperature (Ti/Te<1). We also investigate the effects of electron secondaries from the surface of the spacecraft, such as photoelectrons and/or secondary electrons emitted by the solar wind proton impact. Our results show that the electron secondaries play an important role in the shock formation. The shock disappears when the temperature of the electron secondaries is comparable with the solar wind electron temperature Ts~Te. ¿ American Geophysical Union 1995