Green Propulsion Research at TNO the Netherlands

Abstract

This paper describes the recent theoretical and experimental research by the Netherlands Organisation for Applied Scientific Research (TNO) into green replacements for hydrazine, hydrazine derivatives and nitrogen tetroxide, as propellants for in-space propulsion. The goal of the study was to identify propellants that are capable of outperforming the current propellants for space propulsion and are significantly less hazardous for humans and the environment. Two types of propellants were investigated, being monopropellants and bipropellants. The first section of the paper discusses the propellant selection. Nitromethane was found to be the most promising monopropellant. As bipropellant, a combination of hydrogen peroxide (HP) and ethanol was selected, where the ethanol is rendered hypergolic with hydrogen peroxide. The second part of the paper describes the experimental verification of these propellants by means of engine testing. Initiation of the decomposition of nitromethane was found to be problematic, hypergolic ignition of the hydrogen peroxide and ethanol bipropellant however was successfully demonstrated.

Review of State-of-the-Art Green Monopropellants: For Propulsion Systems Analysts and Designers

“…Typically, methanol is used to control the burning rate of the monopropellant while the ammonium nitrate (AN) is used as a stabilizer [10] beside other stabilizing additives; a new article by M. Claßen et al [11] introduced novel additive promoters of new azido esters and suggested it would improve the total energy and performance of ionic liquid propellants. As an example, the maximum specific impulse of 78 wt% ADN in water mixture (Ionic Liquid) is 192 s when used as monopropellant, while the specific impulse rises to 252 s when methanol (molecular fuel) is added to the mixture, as in the case of LMP-103S (63.4 wt% ADN, 25.4 wt% water and 11.2 wt% methanol) at a nozzle area expansion ratio of 50 [12] as cited in [3]. In the next paragraphs different EILs will be reviewed (i.e., HAN, HAN/HN, HNF, ADN) based on green monopropellants emphasizing on their composition, physical properties, performance, stability of storage and handling, toxicity, material compatibility, ignition methods, and in-flight heritage or proposed missions.…”

“…Moreover, transportability and handling of hydrazine and similar hazardous propellants extend an economic burden on the space industry. Accordingly, greener alternatives that would compensate for these drawbacks are being studied and developed rapidly nowadays [3,4]. Different global entities were involved in accelerating such research activities through various projects and missions such as Green Advanced Space Propulsion (GRASP), Pulsed Chemical Rocket with Green High Performance Propellants (PulCheR), and Replacement of hydrazine for orbital and launcher propulsion systems (RHEFORM) European projects and Green Propellant Infusion Mission (GPIM) technology demonstrator project by NASA.…”

“…Due to their favorable characteristics, green propellants demonstrate higher commercial value by being able to cut costs related to transportation, storage, handling, and further reduces ground operations time. Recently, a more specified definition has been noted by Mayer et al [3], based on the Acute Toxicity Classification (ATC) by the Global Harmonized System of classification and labeling of chemicals (GHS) [6], which denotes that propellants possessing ATC levels of three and safer are considered as green propellants. ATC levels are typically categorized on a 1:5 scale where level one denotes the most toxic class and level five is considered the least toxic class.…”

“…Before discussing each green monopropellant family in detail, relatively different classifications in literature were proposed for green alternatives of hydrazine monopropellant, one of them considered mainly three types: Energetic Ionic Liquids, Hydrogen Peroxide, and Nitrous Oxide by Batonneau et al [7] as cited in [8]. However, Mayer et al [3] further classified propellants including nitrogen compounds with oxygen into two groups: Oxides of Nitrogen subcategory and Nitro Compounds subcategory. The former included mono and dinitrogen oxides (NO, NO 2 , N 2 O, N 2 O 3 , N 2 O 4 , N 2 O 5 ), which were evaluated as potential oxidizers for bipropellant systems; among which the only compound that was considered as potential green propellant was the nitrous oxide (N 2 O) due to its relative nontoxicity (GHS [6] class 5) and being liquid within a wide part of the typically requested temperature-pressure envelope of [−30, +80] • C and [0.1, 3] MPa, respectively.…”

“…The former included mono and dinitrogen oxides (NO, NO 2 , N 2 O, N 2 O 3 , N 2 O 4 , N 2 O 5 ), which were evaluated as potential oxidizers for bipropellant systems; among which the only compound that was considered as potential green propellant was the nitrous oxide (N 2 O) due to its relative nontoxicity (GHS [6] class 5) and being liquid within a wide part of the typically requested temperature-pressure envelope of [−30, +80] • C and [0.1, 3] MPa, respectively. The latter, Nitro Compounds group, was described as organic substances containing dinitrogen monoxide (i.e., hydrocarbons and nitrous oxide) group, such as (mono)nitromethane (CH 3 NO 2 or NM), which was also considered as a promising candidate green propellant being relatively nontoxic (GHS class 4) [3]. Gohardani et al [9] aimed at reviewing and investigating a number of promising green propellants in a part of the paper; the mentioned three candidate propellant categories were hydrogen peroxide, nitrous oxide fuel blends, and ionic liquids.…”