Ten years ago (mid 2011) the classic propellant hydrazine was included in the list of substances of very high concern for authorization (SVHC) by REACH legislation of the European Chemicals Agency (ECHA). Hydrazine is one of the high performance monopropellants with low flame temperature, which makes it an efficient propellant. However, its toxicity to humans and environment has put, firstly, an economic burden on using such propellant during various development and operation phases. Secondly, an ethical burden toward the environment if such sense to be considered. It is worthy to note that hydrazine is not just an appealing efficient propellant for Space-use, but it is also seems to take a critical role in aeronautical military applications such as fueling the auxiliary power units of the F-16 fighters and Eurofighter Typhoon.
Speaking of today in 2021/2022 and from a technical point of view, the economical as well as the environmental hazards concerns are taken seriously into account when considering ‘space mission analysis & design.’ The latter two aspects when coupled are crucial during the conceptualization of a given space mission as well as developing modern spacecraft critical components such as the propulsion systems.
Basically, space industry is currently oriented toward adopting the so-called ‘Green Propellants.’ A very simple technical definition for Green Propellants can state that the propellants possessing no (or very marginal) health concerns or environmental hazards either in storage, transportation, or operation phases of a project lifecycle, are considered to be ‘green’ – this would opt out propellants with high-toxicity like hydrazine, but fossil hydrocarbons are not yet considered ‘non-green’ fuels in the framework of Space propulsion applications in contrary to fuels in automobile industry. More detailed technical definitions can be referenced in the these academic articles: Article 1, Article 2.
Current Green Propellants industry is reaching maturity that several global research efforts have already provided commercially available and space-tested green propellants. Examples are: the US Air Force developed propellant AF-M315E (currently known and commercialized as ASCENT); the European LMP-103S developed by Bradford ECAPS; and the Japanese HNP-family of green monopropellants developed by IHI Aerospace Co., Ltd. These propellants are suitable for spacecraft use in in-space propulsion, usually for the small spacecraft class.
There were rumors among the aerospace European community (particularly since 2017) that EU would ban completely the use of hydrazine by 2021, so far nothing is clear however about this intention.
See also this Metaculus question on a similar ban for the EU.
Will the US propose a ban on hydrazine for spacecraft propulsion by 2025-01-20?
This question resolves positively if any branch of the US federal government makes a formal proposal to ban Hydrazine and Hydrazine-derivative spacecraft fuels before 2025-01-20. It is not necessary for this proposal to recieve a vote or become law to resolve this question.