“Create an artificial ion cloud in interplanetary space for studying the state of the interplanetary medium .. sounding rocket experiments of May 1963.”
It has been proposed to create an artificial ion cloud in interplanetary space for studying the state of the interplanetary medium. New data concerning excitation and ionization by sunlight are given in section 2 for the alkali-earth metals Calcium, Strontium, Barium and for the rare earth Europium which could be used for such an ion cloud. In section 3 the expansion of the artificial cloud in interplanetary space, the interaction of the ion cloud with the interplanetary medium and the minimum masses required are estimated. The results are stated in Table 3. 
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