Preservation of the purity of liquid hydrogen (H2 ), which is used to fuel electrochemical generators of spacecraft power supply systems, during storage and transportation in model ZhVTs-100M railroad tank cars is studied. The quality of liquid H2 at various technological stages of transportation from the railroad tank-car filling plant to the consumer is analyzed. Experimental results are compared with the calculated stepwise increase of impurity N2 and O2 concentrations in the liquid H2. The methodology for calculating the purity of liquid H2 during transportation is clarified based on the assessment. Tanks with improved thermal insulation are proposed for maintaining its quality.