Sentence:  Since there is a continual loss of micrometeoritic material in space because of the radiation effects , there must be a <WSD>continual</WSD> replenishment : otherwise , micrometeorites would have disappeared from interplanetary space . 
Meaning of the word marked with <WSD> tags:  occurring without interruption; chiefly restricted to what recurs regularly or frequently in a prolonged and closely spaced series