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Towards Greener Propulsion: Environmental Categorization of Liquid In-Space Propulsion Systems via Life Cycle Analysis
Abstract
As space activities continue to expand, with increasing numbers of launches and payloads, it becomes crucial to evaluate the environmental consequences of these developments. In this perspective, this study investigates the ground-phase environmental footprint of future in-space liquid bipropellant systems, focusing on MON3/MMH, 98%-HTP/RP-1, 98%-HTP/Ethanol, and N2O/Ethane. A lifecycle analysis from propellant production to the integration of the propulsion system into the launcher for a typical mission scenario identifies key environmental impact hotspots.
The findings reveal that the production phase of MMH stands out as particularly detrimental, primarily due to its energy-demanding distillation process and its specialized, low-volume production tailored for space applications. The MON3/MMH system continues to show the highest contribution when considering the entire phases up to propellant loading due to stringent fuelling and decontamination processes.
In terms of propulsive architecture, tank production, whether using titanium or aluminium, stands out as the primary environmental hotspot for dry architectures, with titanium proving more environmentally disruptive. In contrast, for wet architectures, the production of dry components constitutes most of the environmental impact, accounting for 95% of the total for HTP combinations and 64% for both MON3/MMH and self-pressurizing options.
... Values are normalized and presented as percentages relative to the highest impact option, MON-3/MMH, for all scenarios. These values were primarily derived from the single-score total impact, combining results from 15 impact indicators, as detailed in the related publication [29]. Fig. 6. ...
This paper presents a comprehensive framework for designing in-space propulsion systems, integrating four criteria: global propulsive performance, environmental impact, cost efficiency, and architectural reliability. The study focuses on the emerging class of Orbital Transfer Vehicles to illustrate the application of this method. By examining the synergistic potential of OTVs and greener propellants, the paper addresses different mission scenarios, including LEO, GEO, and lunar missions, with both scientific and commercial objectives. The proposed framework aims to go beyond traditional cost-centric approaches, offering a more complete evaluation method for early design phases. A case study comparing three liquid bipropellant options, pressure-fed MON-3/MMH, 98%-HTP/RP-1, and self-pressurizing N2O/Ethane, demonstrates the utility of the tool. Findings suggest that scientific missions benefit most from 98%-HTP/RP-1, while traditional propellants remain preferable for cost-driven commercial missions to GEO and the MOON, though greener alternatives are competitive for less demanding LEO missions. This innovative framework aims to guide the selection of propulsion systems to achieve greener space missions, aligning traditional performance figures with environmental responsibility.
With a continuously growing number of satellites in orbit, it becomes increasingly important to assess their impacts on the Earth's environment in a standardised manner. While interest in Life Cycle Assessment (LCA) for space missions has gained in strength in the past few years – particularly in Europe – no consensus has yet been reached on a single-score LCA system.
In this thesis, a consensus-based space LCA single-score is created through an international survey of experts. The report demonstrates retroactively the single-score’s use in ecodesigning the Delft University of Technology’s Delfi-n3Xt space mission. Moreover, a discussion is held on ways of implementing the single-score into early design phases.
Overall, this thesis highlights the importance of an easy-to-understand LCA tool for space systems. It shows the necessity for a tool that is implementable during the design phase of the mission, to incentivise space actors to further consider environmental impacts.
The fast-paced growth of the space sector brings in new challenges especially with upcoming complex missions combining multi-orbit deliveries and/or on-orbit servicing such as Active Debris Removal (ADR). Europe has taken up the challenges and is working on extending its launchers portfolio and capabilities. In this framework, a new add-on, the kick stage, confers strategic advantages to the launcher in expanding its missions' range. While many kick stages are currently developed, or already in use worldwide, this paper pays a particular attention to the new ASTRIS kick stage developed and optimized for A6 and its next kick stage generation already under conceptual study, LunaNova, at ArianeGroup Bremen for A6 Evolution. The project takes place under the ESA Future Launchers Preparatory Programme (FLPP) and is already implementing new technologies, namely innovative pressurization system and green propellants which are of special interest here. The paper starts by introducing the kick stage capabilities, especially the LunaNova ones, to then focus on the cost-oriented trade-off performed to select the fuel to use in combination with 98%-HTP to power the LunaNova vehicle. The paper then concludes by discussing the system impacts of implementing green propellants within the operational kick stage life cycle and its possible enhancement (namely the implementation of an e-pump).
This paper analyses the synergy between two innovative technologies: green propellants and electric pump feeding, for a 500 N engine thrust range. The novel approach is then compared to the legacy configuration, i.e., an MMH/NTO pressure fed system. First, a discussion of the benefits and challenges of the different technologies is presented. Subsequently, the proposed configuration relying on green propellants and e-pumps is investigated. After selecting hydrogen peroxide as the baseline oxidiser, a comparative analysis of different fuel candidates is conducted, leading to the selection of propane as fuel. Furthermore, the second part of the paper weights the novel configuration against the standard one and confronts their propulsive performance and mass budget. Results show that the implementation of electric pump feeding can leverage the performance of the selected green propellant outpacing the conventional solution.
This book is a collection of selected applications of the Analytic Hierarchy Process
(AHP) in economic, social, political and technological areas. This volume along
with other volumes on decision making, planning, conflict resolution and forecasting,
rounds out the diversity of application areas of the AHP.
Current research trends have advanced the use of “green propellants” on a wide scale for spacecraft in various space missions; mainly for environmental sustainability and safety concerns. Small satellites, particularly micro and nanosatellites, evolved from passive planetary-orbiting to being able to perform active orbital operations that may require high-thrust impulsive capabilities. Thus, onboard primary and auxiliary propulsion systems capable of performing such orbital operations are required. Novelty in primary propulsion systems design calls for specific attention to miniaturization, which can be achieved, along the above-mentioned orbital transfer capabilities, by utilizing green monopropellants due to their relative high performance together with simplicity, and better storability when compared to gaseous and bi-propellants, especially for miniaturized systems. Owing to the ongoing rapid research activities in the green-propulsion field, it was necessary to extensively study and collect various data of green monopropellants properties and performance that would further assist analysts and designers in the research and development of liquid propulsion systems. This review traces the history and origins of green monopropellants and after intensive study of physicochemical properties of such propellants it was possible to classify green monopropellants to three main classes: Energetic Ionic Liquids (EILs), Liquid NOx Monopropellants, and Hydrogen Peroxide Aqueous Solutions (HPAS). Further, the tabulated data and performance comparisons will provide substantial assistance in using analysis tools—such as: Rocket Propulsion Analysis (RPA) and NASA CEA—for engineers and scientists dealing with chemical propulsion systems analysis and design. Some applications of green monopropellants were discussed through different propulsion systems configurations such as: multi-mode, dual mode, and combined chemical–electric propulsion. Although the in-space demonstrated EILs (i.e., AF-M315E and LMP-103S) are widely proposed and utilized in many space applications, the investigation transpired that NOx fuel blends possess the highest performance, while HPAS yield the lowest performance even compared to hydrazine.
Aligning with the current shift towards greener energy, many space companies are already replacing toxic rocket fuels with greener ones. However, this often implies taking risk in a domain that is rather risk adverse. To help into taking this leap, the tool presented here gives a quick analysis of the different propulsion options able to fulfil certain types of in-space missions. Kick stages are taken as reference system for their prospects in facilitating mission logistics and their abilities to fulfill a wide range of missions. Taking as inputs mission scenarios parameters, the tool evaluates the propulsive options with respect to four figures of merit: propulsive performance, environmental performance, reliability and cost effectiveness. To illustrate the functioning of the tool, five propulsive options with different propellant combinations and feeding architectures are evaluated over three mission scenarios to LEO, GEO and MOON orbits. A final trade-off and system selection reveals that the most suitable propulsion choices vary depending on whether the mission is meant for scientific or commercial purposes.
As an emerging trend, Green Propulsion has been exponentially growing over the last decades in the space sector. This paper assesses different technologies in a trade-off study weighting their applicability to a specific class of upper stage systems currently developed by many companies and often referred to as kick-stages or orbital stages. In a generic two-stage-to-orbit scenario, many launchers require a system able to go the ‘extra mile’ to deliver one or multiple payloads on orbit(s). That is where the kick stage comes into playing a crucial role. The trade-off study reported here is based on a well-known decision-making tool, the Analytical Hierarchy Process, and is divided into two parts: low-thrust class engines such as monopropellants, including pre-mixed blends, usually employed for attitude and reaction control; and high-thrust engines such as hypergolic bi-propellants combinations used for apogee manoeuvres. Hybrid thrusters are also considered in the analysis with a dedicated parallel trade-off.
The growing demand for cheaper space access calls for a more economically and environmentally sustainable approach for launchers. Concurrently, the shift to smaller satellites and the rise of constellations necessitate launchers capable of precise multi-payload/multi-orbit injection. ASCenSIon (Advancing Space Access Capabilities-Reusability and Multiple Satellite Injection), a Marie Skłodowska-Curie Innovative Training Network funded by Horizon 2020 (H2020), aims to respond to these demands. This paper describes the activities explored within ASCenSIon dedicated to developing novel green upper stages with multi-payload/multi-orbit injection capability. The aspects investigated here include the general system architecture, innovative solutions for the propulsion system (e.g., Hybrid Rocket Engines (HREs), green propellants and electric pump feeding), Guidance Navigation and Control (GNC) solutions for the multi-payload/multi-orbit injection capability, and reliability aspects of upper stages. First, relevant space market considerations are raised. Then, solutions for more environmentally friendly propulsion systems are proposed. Since identifying a good substitute for toxic hydrazine recently became a priority, the use of green propellant technologies will be assessed, tackling specific problems such as benchmarked propulsive performances, storability and material compatibility. Another promising solution for future propulsion systems with lower environmental impact are HREs. They bring benefits in terms of flexibility, safety and cost. However, high residual mass, oxidizer-to-fuel ratio (O/F) shift during operation, low regression rate and combustion inefficiency are some of the challenges that still need to be addressed in their application. In addition, electric pump fed systems, powered by green propellants, may be a game-changer technology for future upper stages. Compared to pressure-fed, it can provide improved performance and lower inert mass. With respect to turbopumps, it may also be advantageous in terms of simplicity and costs. On the other hand, battery mass and thermal control represent some of the drawbacks to overcome. Additionally, the implementation of novel GNC solutions is critical to ensure the multi-payload/multi-orbit injection capability. The challenges brought by the design of such a system are presented, including the correlation with the overall upper stage definition. Finally, the reliability of the launchers is a key aspect to protect both the space environment and the safety of the missions. Novel methods for reliability modelling of launchers are discussed and advantageous system architectures are proposed. These novel technologies being jointly assessed, this paper presents a preliminary analysis of the discussed topics and their interconnections within ASCenSIon, aiming at satisfying new requirements for novel green upper stages.
Hydrazine propellant has historically been used as a rocket thruster monopropellant since the mid-1960s. Mission managers are well aware of its characteristics and performance. However, it is a known toxic chemical and a wide effort is underway to reduce and/or eliminate its use worldwide. Several new propellant combinations have been developed in the last few years which tout or promise to provide same or better performance as hydrazine while being "non-toxic" or "green". Yet, there is no consistent definition for what constitutes "non-toxic" or "green", and thus no good figure of merit for which to compare. This paper seeks to review the three major categories of figures of merit, and discusses how they might be used to assess the viability of a propellant.
With the first launch of VEGA approaching, the European launch vehicle family will soon be completed. VEGA aims at transporting small research- and earth observation satellites to Low Earth Orbit (LEO).
Ongoing investigations show the opportunity for a performance improvement of the launcher to cope with the market demand for evolution in P/L mass. Therefore, studies to enhance the capabilities of the launch vehicle were started.
The German Space Administration (DLR) has funded the VENUS (VEGA New Upper Stage) studies on behalf of the German Federal Ministry of Economics and Technology with Astrium Space Transportation as Prime Contractor and the DLR institute for Space Launcher Systems Analysis (SART) as subcontractor, in order to identify and assess the potential of increasing the upper stage performance. The second slice of the study, the so-called VENUS-2 study (support code FKZ50RL0910), was started in July 2009 and has been finalized mid 2011. VENUS-2 aims at investigating possible evolutions of the VEGA-launcher upper stage. In particular, conceptual lay-outs for new storable propellant upper stages have been investigated including engines.
The VENUS-2 study is divided into three study phases. Phase 1 work was focused on conceiving and analysing different new upper stage architectural concept candidates and selecting reference concepts on the basis of trade-offs and by optimization of overall launcher P/L performance. After this phase the main parameters were frozen. Phase 2 focuses on the Conceptual Design during which dedicated stage mechanical designs and trade offs were conducted, as well as thermal studies on the thermal behaviour of the stages, lay-outs of the functional propulsion systems, propellant and helium budgets on the basis of more detailed analyses, needed electrical interfaces between upper stage and avionics equipment, trade-offs for the separation systems, dedicated designs for the engines AESTUS-2 and BERTA, resulting mass budgets, and adapted launcher performance characteristics in order to update the maximum payload mass. Further, in Phase 3 development logics and plans were established.
In parallel to the study work experimental demonstration on new injector concepts addressing the BERTA engine have been conducted. Article available at: http://elib.dlr.de/71266/
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