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Modular Impulsive Green Monopropellant Propulsion System (MIMPS-G): For CubeSats in LEO and to the Moon
Modular Impulsive Green Monopropellant Propulsion System (MIMPS-G): For CubeSats in LEO and to...
Nosseir, Ahmed E. S.;Cervone, Angelo;Pasini, Angelo
aerospace Article Modular Impulsive Green Monopropellant Propulsion System (MIMPS-G): For CubeSats in LEO and to the Moon 1 , 2 , 1 , 2 , Ahmed E. S. Nosseir * , Angelo Cervone * and Angelo Pasini * Department of Space Engineering, Faculty of Aerospace Engineering, Delft University of Technology (TU Delft), 2629 Delft, The Netherlands Sede di Ingegneria Aerospaziale, Dipt. di Ingegneria Civile e Industriale, Università di Pisa (UniPi), 56122 Pisa, Italy * Correspondence: email@example.com or firstname.lastname@example.org (A.E.S.N.); email@example.com (A.C.); firstname.lastname@example.org (A.P.) Abstract: Green propellants are currently considered as enabling technology that is revolutioniz- ing the development of high-performance space propulsion, especially for small-sized spacecraft. Modern space missions, either in LEO or interplanetary, require relatively high-thrust and impulsive capabilities to provide better control on the spacecraft, and to overcome the growing challenges, particularly related to overcrowded LEOs, and to modern space application orbital maneuver require- ments. Green monopropellants are gaining momentum in the design and development of small and modular liquid propulsion systems, especially for CubeSats, due to their favorable thermophysical properties and relatively high performance when compared to gaseous propellants, and perhaps simpler management when compared to bipropellants. Accordingly, a novel high-thrust modular impulsive green monopropellant propulsion system with a micro electric pump feed cycle is pro- posed. MIMPS-G500mN is designed to be capable of delivering 0.5 N thrust and offers theoretical total impulse I from 850 to 1350 N s per 1U and >3000 N s per 2U depending on the burnt mono- tot Citation: Nosseir, A.E.S.; Cervone, propellant, which makes it a candidate for various LEO satellites as well as future Moon missions. A.; Pasini, A. Modular Impulsive Green monopropellant ASCENT (formerly AF-M315E), as well as HAN and ADN-based alternatives Green Monopropellant Propulsion (i.e., HNP225 and LMP-103S) were proposed in the preliminary design and system analysis. The System (MIMPS-G): For CubeSats in LEO and to the Moon. Aerospace 2021, article will present state-of-the-art green monopropellants in the (EIL) Energetic Ionic Liquid class 8, 169. https://doi.org/10.3390/ and a trade-off study for proposed propellants. System analysis and design of MIMPS-G500mN will aerospace8060169 be discussed in detail, and the article will conclude with a market survey on small satellites green monopropellant propulsion systems and commercial off-the-shelf thrusters. Academic Editor: Filippo Maggi Keywords: green monopropellant; chemical rocket propulsion; CubeSats; small satellites; micro Received: 12 May 2021 electric pump feed cycle Accepted: 17 June 2021 Published: 19 June 2021 Publisher’s Note: MDPI stays neutral 1. Introduction with regard to jurisdictional claims in CubeSat propulsion is evolving to fulﬁll the requirements of modern space missions published maps and institutional afﬁl- and applications that demand propulsion capabilities to enable active orbital operations, iations. such as orbital altitude and inclination changes, orbital transfers, formation ﬂying, ren- dezvous operations–generally, operations requiring high-thrust impulsive maneuvers. An example for commercial CubeSats utilizing a green propulsion system, namely HPGP by ECAPS, is the SkySat LEO imaging constellation by Planet Lab from 2016 to 2020 . Other Copyright: © 2021 by the authors. science missions for CubeSats utilizing a propulsion system are MarCO Mars deep-space Licensee MDPI, Basel, Switzerland. CubeSat utilizing a cold-gas propulsion system launched in May 2018 , and Pathﬁnder This article is an open access article Technology Demonstrator (PTD) by NASA, launched in January 2021 which utilizes the distributed under the terms and Hydros-C water-based propulsion system . Challenges facing this evolution include, conditions of the Creative Commons as an example, the need for design-modularity and components miniaturization. Design Attribution (CC BY) license (https:// modularity may be considered as a cornerstone for rapid fabrication and assembly of creativecommons.org/licenses/by/ 4.0/). Aerospace 2021, 8, 169. https://doi.org/10.3390/aerospace8060169 https://www.mdpi.com/journal/aerospace Aerospace 2021, 8, 169 2 of 26 subsystems and components, which usually reduce development costs and time. Miniatur- Aerospace 2021, 8, 169 2 of 27 ization of components is crucial to the space industry in general, since nowadays every gram of payload mass to orbit may have a signiﬁcant monetary value, adding to that the presence of onboard size restrictions. Design modularity and miniaturization is a of subsystems and components, which usually reduce development costs and time. Min- major point of focus for various research work in the space propulsion ﬁeld in general, iaturization of components is crucial to the space industry in general, since nowadays every gra either for m of electric payload mass to orbi propulsion [4,t ma 5] or y ha for ve a chemical significa pr nt moneta opulsion ry val in standalone ue, adding to systems or that the presence of onboard size restrictions. Design modularity and miniaturization is a in multimode systems, as extensively studied by Rovey, J. L. et al. . On another note, major point of focus for various research work in the space propulsion field in general, green monopropellants are the current trend in liquid propellant propulsion for small either for electric propulsion [4,5] or for chemical propulsion in standalone systems or in satellites, either in scientiﬁc or industrial research and development as well as commercial multimode systems, as extensively studied by Rovey, J. L. et al. . On another note, green activities, due to their safety, stability, storability, relative design simplicity, as well as high monopropellants are the current trend in liquid propellant propulsion for small satellites, performance, and may soon face global legal regulations for a greener environment–as either in scientific or industrial research and development as well as commercial activities, expected by the authors. These facts were the motive behind the design of (MIMPS-G) the due to their safety, stability, storability, relative design simplicity, as well as high perfor- Modular Impulsive Propulsion System to utilize Green monopropellants and is a prospec- mance, and may soon face global legal regulations for a greener environment–as expected tive system for micro and nano spacecraft, particularly CubeSats, requiring a modular by the authors. These facts were the motive behind the design of (MIMPS-G) the Modular propulsion system for high-thrust impulsive orbital maneuvers. From the study of the Impulsive Propulsion System to utilize Green monopropellants and is a prospective sys- tem for micro market andand nan the curr o spacecraft, partic ent state-of-the-art ularlpr y CubeS oducts ats in , re the quir gr ing een a modu propulsion lar propuls industry ion , it was syst deemed em fornecessary high-thrust to im design pulsive o a gr rbit een al man monopr euver opellant s. From the propulsion study of the system market that an would d help the current state-of-the-art products in the green propulsion industry, it was deemed nec- in solving several challenges related to acquiring higher performances and lower costs as essary to design a green monopropellant propulsion system that would help in solving well as demonstrating competitive advantages to currently proposed systems, as will be several challenges related to acquiring higher performances and lower costs as well as discussed in Sections 4 and 5 of this manuscript. The design and development plans have demonstrating competitive advantages to currently proposed systems, as will be dis- taken place within a research work carried out at the beginning of the year 2020 between cussed in Section 4 and 5 of this manuscript. The design and development plans have the Department of Aerospace Engineering in the University of Pisa and the Department of taken place within a research work carried out at the beginning of the year 2020 between Space Engineering of the Aerospace Engineering Faculty in TU Delft. the Department of Aerospace Engineering in the University of Pisa and the Department The baseline design of MIMPS-G500mN is a standard 1U CubeSat size that can of Space Engineering of the Aerospace Engineering Faculty in TU Delft. be expanded or clustered depending on the spacecraft size, required thrust level, and The baseline design of MIMPS-G500mN is a standard 1U CubeSat size that can be mission’s DV budget. One of the critical components in this propulsion system that expanded or clustered depending on the spacecraft size, required thrust level, and mis- required special attention and deep analysis was the feed and pressurization system. It was sion’s ΔV budget. One of the critical components in this propulsion system that required special attention found that convent and deep analy ional systems sis was the such feed and pressu as stored gas or rizat blow-down ion system. pr It was found essure-fed systems that conventional systems such as stored gas or blow-down pressure-fed systems were were introducing more limitations over time, especially due to the increasing performance introducing more limitations over time, especially due to the increasing performance re- requirements and the size and mass restrictions on the inert parts of CubeSats. Foreseeing quirements and the size and mass restrictions on the inert parts of CubeSats. Foreseeing that eventually, designers would face design-simplicity trade-offs in favor of performance, that eventually, designers would face design-simplicity trade-offs in favor of perfor- it was time to investigate, study, and analyze unconventional and more complex feed mance, it was time to investigate, study, and analyze unconventional and more complex and pressurization systems for small-sized spacecraft. Thus, in the preliminary design of feed and pressurization systems for small-sized spacecraft. Thus, in the preliminary de- MIMPS-G500mN, Figure 1 and Video S1, autogenous pressurization and micro electric sign of MIMPS-G500mN, Figure 1 and Video S1, autogenous pressurization and micro pump feed (micro e-Pump feed cycle) were proposed using commercial off-the-shelf electric pump feed (micro e-Pump feed cycle) were proposed using commercial off-the- (COTS) components. shelf (COTS) components. Figure 1. MIMPS-G500mN realistic render. Aerospace 2021, 8, 169 3 of 26 In the following sections of this article, the three proposed green monopropellants, belonging to the Energetic Ionic Liquids (EILs) class, will be reviewed emphasizing their physical properties, performance and their development status. These three selected propellants were a result of a trade-off study that will be discussed in detail in Section 1.2. Furthermore, the feed and pressurization systems of the designed propulsion system will be discussed, and the basic concepts will be elaborated on. The rest of the article will discuss the system analysis, requirements identiﬁcation, design methodology, and preliminary design process and the results will be numerically tabulated. Finally, a market survey on the state-of-the-art monopropellant propulsion systems for small-sized spacecraft, as well as commercial off-the-shelf green monopropellant thrusters will be presented, highlighting the main performance parameters and technical speciﬁcations of such systems and thrusters to serve as a reference for our proposed propulsion system MIMPS-G500mN, as well as a reference for the readers of this manuscript. This article presents a more detailed analysis and results and extends the research work presented by the authors in the conference papers [7–9]. 1.1. Space Mission Requirments Spacecraft propulsion systems are typically designed and developed according to a predeﬁned set of requirements dictated by the space mission analysis and design phase. Usually, any modiﬁcation or compromise during the project development affects the design process and outcomes of the spacecraft’s different systems and subsystems in order to maintain the strict requirements of the mission orbital operations. In addition to that, the size restrictions in micro- and nanosatellites inherit more challenges and limitations on the spacecraft systems’ development, especially the propulsion system and its subsystems, which in turn leads to the development of a “single-purpose” or “one-time-use” micro propulsion systems that are solely developed for a particular mission. To overcome such challenges, scientists and engineers are focused on optimizing various spacecraft component designs such as the power generation and storage systems, electronics, communication and control systems, and structural interfaces onboard the spacecraft to provide more integration ﬂexibility and adaptability. The propulsion sys- tem remains one of the most challenging parts to optimize in terms of maintaining high performance and suitable costs. In the last two years, a lot of scientiﬁc efforts were put together in order to reach a new level of optimization through pushing the boundaries of systems engineering and bending the norms of conventional design and manufacturing as well as investigating new propulsion subsystems operation concepts. It was found that it is time to accept drastic changes and to consider trading off design simplicity for high-performance by manipulating current technologies to adapt more complex propulsion feed and pressurization systems as well as new propellant storage tank designs. In the design of MIMPS-G, the greatest focus was put on modularity and expandability as key design elements to enable ﬂexibility and adaptation of the propulsion system to various space mission requirements, especially the ones deﬁned by modern orbital operations from the point of view of small satellites and CubeSats. Accordingly, MIMPS-G is not a “single-purpose” or “one-time-use” propulsions system, otherwise, it is designed to fulﬁll different space missions with various DV requirements relying on the modularity and expandability properties, where the 1U main propulsion module is capable of delivering at least total impulse of I = 850 N s with the possibility to add extension tanks of at least tot I = 1100 N s per tank, theoretical values. The baseline design of the 1U main propulsion tot module relied on studying orbital maneuver requirements of different CubeSat missions; examples are presented in the following paragraph. Modern CubeSat missions have evolved from technology demonstration missions to real missions involving long-life commercial applications and scientiﬁc space explo- ration. Big economies are growing around “Earth Observation Services” as an example, that are mainly provided by private sector players, thanks to the small satellites industry, particularly CubeSats. Such commercial missions that rely on operating small satellite Aerospace 2021, 8, 169 4 of 26 constellations in signiﬁcantly low earth orbits (LEO) require a dedicated propulsion system onboard the spacecraft to ensure long life and maximum proﬁtability. These types of missions and applications require active orbital operations such as formation ﬂying, atti- tude control, and drag compensation, especially in orbits subject to rigorous atmospheric drag. Recently, due to the growing number of satellite constellations, obstacle avoidance maneuvers in crowded LEO orbits impose high-thrust impulsive capabilities. Table 1 shows DV requirements for drag compensation and lifetime extension of nanosatellites in LEO. Tables 1 and 2 present data derived by Nardini, F. T. et al. . Table 1 considered that the 1U and 3U spacecraft are of 1 and 4 kg, respectively, while the 8 and 10 kg space- craft are of 6U standard size, all with the small cross-section facing the ﬂight path; Data were derived using the NRLMSISE-00 atmospheric model, assuming a drag coefﬁcient C = 2.2 and no deployable panels for standard CubeSat sizes. As for scientiﬁc deep-space exploration demonstrated in Lunar and interplanetary missions, orbital transfers require a signiﬁcant DV budget. Table 2 presents different orbital transfer maneuvers and the required DV utilizing relatively high-thrust impulsive shot maneuvers. Clear assumptions were not mentioned or explained by the source  regarding the derivation of some data in Tables 1 and 2, such as the precise method of calculation for the lifetime and the burn duration in case of impulsive shot maneuvers; the values of DV for LEO to GEO and LEO to Lunar Orbit transfers are quite similar and clear calculations are not explained, therefore these data were taken as generic reference and were not applied in any calculations during the design phase of our propulsion system. Table 1. Drag compensation for nanosatellites in LEO . Lifetime DV for 50% Increase Orbit Altitude (km) Spacecraft Mass (kg) (y m d) Life-Time(m s ) 1 1.3 d 9.28 4 4.4 d 7.92 8 2.8 d 8.80 10 3 d 8.57 1 21.8 d 11.96 4 2 m 26 d 11.67 8 1 m 22 d 11.77 10 1 m 26 d 15.76 1 6 m 13 d 14.20 4 2 y 1 m 11 d 13.77 8 1 y 3 m 12 d 14.01 10 1 y 4 m 18 d 14.01 Table 2. Orbital changes DV using impulsive shot maneuvers [10,11]. Maneuvers DV (km s ) LEO to GEO 3.95 (no plane change) GTO to GEO 1.5 (no plane change) LEO to Earth Escape 3.2 * LEO to Lunar Orbit 3.9 GTO to Lunar Orbit 1.7 Calculated using Edelbaum’s equation. * For jet exhaust to initial circular velocity ratio = 10. 1.2. Green Monopropellants Trade-Off Study ASCENT or the Advanced SpaceCraft Energetic Non-Toxic propellant, formerly known as AF-M315E for Air Force Monopropellant, was developed by the Air Force Research Laboratory AFRL in 1998 . This propellant is a hydroxylammonium nitrate HAN-based green monopropellant, and when decomposed produces an adiabatic ﬂame temperature of about 2100 K which is much higher than that of the classic monopropel- lant hydrazine (~1200 K). ASCENT offers a 63% increase in density and a 13% increase in speciﬁc impulse over hydrazine , which makes it better in the miniaturization of Aerospace 2021, 8, 169 5 of 26 propulsion systems over the latter. The theoretical vacuum speciﬁc impulse I ranges sp from 260 to 270 s depending on the evaluation conditions. This propellant possesses high solubility and negligible vapor pressure of all its solution constituents, thus promoting high mixture stability at a wide range of temperatures, and low toxicity hazards in development and testing environments . The favorable solubility and vapor pressure properties were found to be interesting, particularly for the micro electric pump feed system development. An advantage ASCENT possesses over most current state-of-the-art green propellants is its maturity. Thorough development of HAN-based propellants has taken place since the beginning of the development program of the Liquid Gun Propellants (LGP) by the U.S. Army until reaching this product and was tested in space on 1 N and 22 N thrusters through the GPIM Green propellant Infusion Mission launched in 2019 . LMP-103S is the most mature among the ammonium dinitramide ADN-based green propellants and was qualiﬁed by ESA the European Space Agency and was in-space demon- strated through the High-Performance Propulsion System (HPGP) on Mango-PRISMA satellite launched in June 2010 [16,17]. Advantages of LMP-103S over ASCENT include lower combustion temperature which allows using materials with lower melting point and simpler designs for the thruster development. The adiabatic ﬂame temperature of LMP-103S is around 1900 K while its theoretical vacuum speciﬁc impulse I is about sp 250 s. FLP-103, 105, 106, and 107 are other examples of ADN-based propellants that were developed by the Swedish Defense Research Agency (FOI) in Europe in 1997 [18–20]. FLP-family of propellants possess thermophysical properties close to LMP-103S and their performance and composition are highlighted in Table 3. In addition, ADN-based green monopropellants showed ﬂexibility in using different ignition techniques other than cat- alytic decomposition, as demonstrated in lab experiments [16,21]; this may allow for the development of novel monopropellant thruster designs. Table 3. ADN-based monopropellants properties [18,22,23] (ideal vacuum I by  using NASA sp CEA @ 2.0 MPa chamber pressure, 50:1 expansion ratio assuming frozen condition ). r rI T sp c Propellant Formulation I (s) sp 3 3 (g cm ) (g s cm ) (K) (1) ( 2) (6) LMP-103S 63.0% 18.4% 18.6% 252 1.24 312.48 1903 (1) ( 2) (5) FLP-103 63.4% 11.2% 25.4% 254 1.31 332.74 2033 (1) (3) (5) FLP-106 64.6% 11.5% 23.9% 255 1.357 344.6 2087 (1) (4) (5) FLP-107 65.4% 9.3% 25.3% 258 1.351 348.5 2142 (1) (2) (3) (4) (5) (6) ADN. Methanol. MMF. DMF. Water. Ammonia (aq. 25% concentration). @ 20 C. HNP (Highly stable Non detonating Propellant) is a HAN/HN-based family of green monopropellants developed by IHI Aerospace of Japan. This family includes HNP209, HNP221, and HNP225, and they are formulated from hydroxyl ammonium nitrate (HAN), hydrazinium nitrate (HN), methanol, and water . HNP225 is the one among the family with the least adiabatic ﬂame temperature, approximately 1000 K, even less than hydrazine (~1200 K), and delivers theoretical vacuum speciﬁc impulse I al- sp most 200 s [24,25], properties shown in Table 4. The low-temperature combustion gasses of HNP225 allowed for the development of low-cost 3D printed thrusters since the require- ment for high heat resistant materials for the thruster ’s combustion chamber is no longer present . The HNP family of green monopropellants ignite using catalytic decomposi- tion. Igarashi et al. 2017  performed tests with newly developed proprietary catalysts and showed excellent response and stability compared to hydrazine, either in pulsed mode operation or continuous mode, with preheating temperatures starting from 200 C for HNP221 and HNP225 monopropellants. HNP2xx family performance chart represented in Figure 2 provides for comparison with hydrazine and state-of-the-art EILs, as well as highlighting the melting point of Inconel 625. Aerospace 2021, 8, 169 6 of 27 . The HNP family of green monopropellants ignite using catalytic decomposition. Iga- rashi et al. 2017  performed tests with newly developed proprietary catalysts and showed excellent response and stability compared to hydrazine, either in pulsed mode operation or continuous mode, with preheating temperatures starting from 200 °C for HNP221 and HNP225 monopropellants. HNP2xx family performance chart represented in Figure 2 provides for comparison with hydrazine and state-of-the-art EILs, as well as Aerospace 2021, 8, 169 6 of 26 highlighting the melting point of Inconel 625. Table 4. Performance and physical properties of HNP2xx green monopropellants family  as cited in . Table 4. Performance and physical properties of HNP2xx green monopropellants family  as cited in . Theoretical Density Volumetric ρIsp Chamber Temp. Propellant Vacuum ρ Theoretical Density −3 Volumetric (g s cm ) rI Chamber Tc (K) T emp. sp −3 Propellant Vacuum r Isp (s) (g cm ) T (K) (g s cm ) I (s) (g cm ) sp HNP209 260 1.32 343 ~1900 HNP209 260 1.32 343 ~1900 HNP221 241 1.22 294 1394 HNP221 241 1.22 294 1394 HNP225 213 1.16 245 990 HNP225 213 1.16 245 990 @ 1.0 MPa chamber pressure, 100:1 expansion ratio, and ideal vacuum conditions. @ 1.0 MPa chamber pressure, 100:1 expansion ratio, and ideal vacuum conditions. Figure 2. HNP2xx green monopropellants family performance chart compared to other EILs. Figure 2. HNP2xx green monopropellants family performance chart compared to other EILs. Adapted from Igarashi and Matsuura 2017  with permission. Adapted from Igarashi and Matsuura 2017  with permission. Among the state-of-the-art green monopropellants surveyed above, four EILs were Among the state-of-the-art green monopropellants surveyed above, four EILs were considered for a trade-off study, Table 5, either for their maturity or for their promising considered for a trade-off study, Table 5, either for their maturity or for their promising potential. During the process of nominating candidate propellants for the propulsion potential. During the process of nominating candidate propellants for the propulsion sys- system design, the rocket performance characteristics of each propellant (such as the tem design, the rocket performance characteristics of each propellant (such as the volu- volumetric speciﬁc impulse) were not the main focus as the selection criteria. Signiﬁcant metric specific impulse) were not the main focus as the selection criteria. Significant atten- attention was put on the propellants’ thermochemical characteristics (i.e., the adiabatic tion was put on the propellants’ thermochemical characteristics (i.e., the adiabatic flame ﬂame temperature) since the lower adiabatic ﬂame temperature would impact the thruster temperature) since the lower adiabatic flame temperature would impact the thruster de- design simplicity as well as mass and costs reduction. The rest of the selection aspects such sign simplicity as well as mass and costs reduction. The rest of the selection aspects such as operation pressure-temperature conditions, service temperature and vapor pressure were as operation pressure-temperature conditions, service temperature and vapor pressure placed according to the typical requirements of the spacecraft propulsion systems under were placed according to the typical requirements of the spacecraft propulsion systems study. The characteristics of the proposed EIL green monopropellants for MIMPS-G500mN under study. The characteristics of the proposed EIL green monopropellants for MIMPS- propellant trade-off study and the propellants trade-off requirements are presented in G500mN propellant trade-off study and the propellants trade-off requirements are pre- Tables 5 and 6, respectively. sented in Tables 5 and 6, respectively. Table 5. Performance and physical properties of the proposed EIL green monopropellants for MIMPS-G500mN [14,16,21,25] as cited in . Theoretical Density Volumetric Chamber Freezing Vapor Propellant Vacuum r rI Temp. Temp. Pressure Maturity sp 3 3 I (s) (g cm ) (g s cm ) T (K) T ( C) (kPa) sp c AF-M315E 266 1.47 391 2166 <