Modern spacecraft and launch vehicle design is more oriented towards reducing system-level design and assembly complexities. In order to maintain high overall system performance while reducing these complexities, the use of smart materials and smart structural components is a well-known practice and is currently of rising interest to space systems' designers. The paper discusses a concept of smart space structures, in particular, a carbon fiber composites structure embedded with Optical Fiber Sensors (OFS) for spacecraft and launch vehicle applications. This study highlights the operational requirements for such tank and the smart features enabled by the optical fiber sensors. For the latter aspect, a quantitative comparison between Fiber Bragg Grating sensors (FBGs) and Distributed Optical Fiber Sensors (DOFS) based on Optical Frequency Domain Reflectometry (OFDR) is presented to state their core performance parameters, such as the sensitivity, sensing range, dynamic measurement capability, and spatial resolution. The increased performance and reliability in harsh environments associated with fiber optic sensors come with a reduction in size, mass, and power consumption compared to the conventional electronic sensors. Optical fiber sensors embedded in carbon fiber structures have proven their capability in providing accurate real-time measurements of temperature and monitoring structural integrity while detecting precisely possible points of rupture and failure as discussed and demonstrated in the literature review. The applications of fiber optic sensing in smart propellant tanks may extend to detecting fluid leakage, also providing increased precision in propellant gauging through temperature mapping, and can be used in on-ground qualification, pre-flight testing, as well as in-orbit operation, condition, and structural health monitoring. The article presents a statement for an optimal FOS embedding approach in composite pressure vessels and discusses the related placement and orientation method for the fiber optic sensors, coupled with a one component simplified analytical stress-strain transfer model deriving the stress component along the maximum principal direction (i.e., σ_MaxPrincipal). The novel approach is believed to serve the optimal employment of embedded FOS in composite structures, e.g., pressure vessels and light-weight structures in spacecraft, among other applications. The simplified model is believed to pave the way for effective data interpretation and processing, utilizing the available limited computational resources on-board the spacecraft.

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Modern spacecraft systems and launch vehicle design is more oriented towards reducing system-level design and assembly complexities. In order to maintain high overall system performance while reducing these complexities, the use of smart materials and smart structural components is becoming of more interest to space systems’ designers. The paper will present a concept of smart space structures, in particular carbon fiber composites embedded with Optical Fiber Sensors (OFS) for spacecraft and launch vehicle applications. Although the application is of interest as well to electric and hybrid propulsion with suitability for a variety of relevant propellants, the case study presented is on smart propellant tanks to be used in launch vehicle’s upper-stage chemical propulsion, utilizing gaseous and liquid fluids with specific interest in green propellants (i.e., EIL and NOx classes). This study will discuss the typical mission and operational requirements for such tanks and the smart features enabled by the optical fiber sensors. For the latter aspect, a quantitative comparison between Fiber Bragg Grating sensors (FBGs) and Distributed Optical Fiber Sensors (DOFS) based on Optical Frequency Domain Reflectometry (OFDR) is presented to highlight their core performance parameters, such as the sensing range and spatial resolution. The proposed smart tanks utilizing optical fiber sensors are found to be capable of providing precise readings of static and dynamic strain as well as temperatures on a wide range. The increased performance and reliability come with a reduction in size, mass, and power consumption compared to the conventional electronic sensors. Optical fiber sensors embedded in carbon fiber structures have proved capability in providing accurate real-time measurements of temperature and monitoring structural integrity while detecting precisely possible points of rupture and failure. The applications of fiber optic sensing in smart propellant tanks may extend to detecting fluid leakage and providing increased precision in propellant gauging and can be used in on-ground qualification, pre-flight testing, as well as in-orbit operation and health monitoring.@en

Green propellants are currently considered as enabling technology that is revolutionizing 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 requirements. 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 proposed. MIMPS-G500mN is designed to be capable of delivering 0.5 N thrust and offers theoretical total impulse I_Tot from 850 to 1350 N s per 1U and >3000 N s per 2U depending on the burnt monopropellant, which makes it a candidate for various LEO satellites as well as future Moon missions. Green monopropellant ASCENT (formerly AF-M315E), as well as HAN and ADN-based alternatives (i.e., HNP225 and LMP-103S) were proposed in the preliminary design and system analysis. The article will present state-of-the-art green monopropellants in the (EIL) Energetic Ionic Liquid class and a trade-off study for proposed propellants. System analysis and design of MIMPS-G500mN will 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.

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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.

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Innovation in small-satellite modern space missions and applications require propulsion capabilities to enable active operations in orbit, such as formation flying, rendezvous operations, orbital altitude & inclination changes, and orbital transfers,– generally, operations demanding high-thrust impulsive maneuvers. In addition, Green-monopropellants are current state-of-the-art of liquid propellants for small satellites space propulsion due to their safety, stability, storability, relative design simplicity, and high performance. These facts were the motive behind the design of the Modular Impulsive Propulsion System– namely MIMPS-G – that utilizes Green-monopropellants and is a prospect solution for micro- and nano- spacecraft, particularly CubeSats, requiring a modular propulsion system for high-thrust impulsive orbital maneuvers. The baseline design is a standard 1U that can be expanded depending on the spacecraft size, required thrust level, and mission’s ΔV requirements. System analysis and preliminary design of MIMPS-G are discussed, and system architecture is presented. Different pressurization-systems are investigated – conventional and unconventional relative to small-satellites – emphasizing on autogenous-pressurization system utilizing micro electric pump, since the choice of the pressurization-system will further affect the propulsion system overall performance, onboard power consumption, and the spacecraft size optimization. A tradeoff study with regards to the performance and characteristics of suitable monopropellants, to be utilized by MIMPS-G, is carried out to give insights for system design and architecture possibilities, as well as future studies concerned with monopropellant propulsion systems for various classes of space propulsion. Finally, candidate propulsion system utilizing a 0.5 N thruster – designated as MIMPS-G500mN – is introduced elaborating system’s architecture, analysis, design, and CAD models. MIMPS-G500mN offers total impulse 퐼푡표푡 ≅ 850 to 1350 N.s per 1U or >3000 푁.푠 per 2U expanded-layout depending on used propellant, which makes the latter a modular expandable propulsion system suitable for Lunar missions. Comparative results of the propulsion system properties using different monopropellants are tabulated – focusing on alternatives for the highly stable Hydroxyl-ammonium nitrate (HAN-) based monopropellant AF-M315E, that is the state-of-art of green-monopropellants.@en