Recent rocket and space shuttle experiments have demonstrated the capability to launch electron beams of moderate power (100 W to 10 kW) into the earth's ionosphere and magnetosphere. In this letter we describe how such beams, when fired from rockets or satellites, can create significant ionization in the E and F-regions of the ionosphere. Through proper selection of beam-related parameters, an interesting variety of plasma density structures, including plasma sheets and plasma filaments, can be created and studied over periods of 30 minutes to 1 hour, depending on the rate of plasma recombination and the density of the ambient plasma. Observations of these structures can give new information relating to the physics of plasma density structures in the ionosphere and the effects these features have upon the scattering of radio waves. It is also possible that observations of the density structures will provide a new means for studying neutral winds and electrodynamic phenomena in the ionosphere.