Static firing tests of oxygen-hydrogen propulsion units with propellant tank load of up to 2700 kg of hydrogen are run with special safety precautions and using emergency test protection system covering up to 60% of contingencies. Test on propulsion units with higher hydrogen propellant loads (up to 7000 kg) require additional safety measures, based on improved effectiveness of the fire and explosion prevention systems, emergency protection, and the coverage ratio for emergency (off-nominal) situations. The key factors for improving off-nominal situations coverage ratio during tests are research into systems for earlier detection of hydrogen leaks and the use of inhibitors with nitrogen as the phlegmatizing agent to prevent explosion of the hydrogen/air (oxygen) mixtures. The paper presents results of studies into systems for early detection of hydrogen leaks and design of monitoring equipment based on fiber optics and microcavity structures that have higher speed of response, selectivity, immunity to noise and reliability. Key words: propulsion system, safety, emergency protection system, off-nominal situation, hydrogen leak, fiber-optic technology.
