scope:

A major problem in designing a cryogenic system in a spacecraft or launch vehicle is avoiding back-pressure buildup, which will affect the ability to service and deservice the vehicle with cryogenic reactants. Servicing lines should be sized adequately for an existing baseline system; then the baseline tubing should be oversized to accommodate increased fluid flow rates that can result from new equipment or changes in requirements. If these accommodations are not part of the initial design, servicing or venting paths may need to be added later.