This part of ISO 15859 specifies limits for the chemical composition and physical properties of propellants based on nitrogen tetroxide (N2O4)-based propellants and establishes the sampling and test requirements applicable for the verification of the nitrogen tetroxide composition. This part of ISO 15859 is applicable to N2O4-based propellants, used as oxidizers in propellant systems of space systems as well as in both flight hardware and ground facilities, systems and equipment, of the following types and grades. — Types — NTO: N2O4 with red-brown colour, — MON-1: N2O4 and NO with green colour, — MON-3: N2O4 and NO with green colour, — MON-10: N2O4 and NO with green colour, — MON-25: N2O4 and NO with green colour; — Grades — standard: no iron requirement, — low-iron: 0,5 μg/g or 1,0 μg/g iron maximum. This part of ISO 15859 is applicable to influents only within the specified limits herein. This part of ISO 15859 is applicable to any sampling operation required to ensure that, when the fluid enters the launch vehicle or spacecraft, the fluid composition complies with the limits provided hereafter or with any technical specification agreed to for a particular use. NOTE NTO is the acronym for nitrogen tetroxide and MON is the acronym for mixed oxides of nitrogen.