In recent years, spacecraft launches have increased significantly, leading to an increased risk of orbital space debris (OSD) collision, translating into further growth in OSD. With the recent space legislation reducing satellites' end of life period in orbit from 25 to 5 years and with the current OSD amounting currently to nearly 130 million pieces, there emerges the imperative need to reduce and manage OSD significantly. Even without the potential future launches, tracked OSD by itself is alarming and requires intervention and abrupt mitigation. This Review highlights the type of pollutants, including spacecraft combustion pollution due to re-entry to earth and emissions from spacecraft thrusters that lead to global warming and ozone layer depletion, mitigation technologies and pollution prevention methods to reduce OSD, spacecraft shield enhancement, and use of green fuel alternatives to launch spacecrafts with negligible air pollutant emissions. 3686 acsomega ACS Omega ACS Omega American Chemical Society PMC10851386 10851386 10851386 38343957 10.1021/acsomega.3c06887 Pollution Effects and Management of Orbital Space Debris Shareefdeen Zarook 1 * Al-Najjar Hadeel 1 1 Department of Chemical and Biological Engineering, American University of Sharjah, P.O. Box 26666, Sharjah, United Arab Emirates * Email: zshareefdeen@aus.edu . 25 1 2024 9 5 5127 5127–5141 9 2 2024 © 2024 The Authors. 24 There are several factors and forces that can act on a satellite and affect its intended trajectory and angle of orientation, including the sun’s gravitational force, the moon’s gravitational force, other space debris heading uncontrollably toward the satellite, a malfunction in the solar panels due to shadow phase or damages due to collision with OSD, malfunction of the batteries due to overuse, or any other causes resulting in cutoffs to sunlight access. By performing the required maneuvers to adjust in case of any potential collisions, these systems ensure that the satellite is in its orbit path. 15 , 16 Besides ensuring that the satellite is kept in its dedicated orbit, spin-stabilized systems also keep the satellite pointed toward its planned orientation and direction by ensuring that its antenna is pointing toward the intended direction. 16 3.0. Cosmic and Space Pollution 3.1. Space Light Pollution According to Wall, anthropogenic activities resulted in a 10% increase in light pollution in the space atmosphere, and astronauts reported that this pollution can be seen without the help of any magnifying devices, resulting in disruption to their work due to spacecraft light trails. 4 The currently reported night sky pollution already exceeded the allowable limit set by the International Astronaut Union (IAU), even without further spacecraft launches. 11 Solid rocket fuels are considered the worst in terms of space emissions, as they result in the generation of not only Al 2 O 3 but also sulfate oxides, etc. Alumina pollution (Al 2 O 3 ) from solid rocket motors (SRM) results in two distinct sources, SRM dust (which ranges in size from 1 to 50 μm), and SRM slag, which results in particles up to a few centimeters in size. Emission of these particles in space at high velocities can result in potential collision threats with other space objects, leading to an expansion in OSD cloud volume. Depending on the type of hydrocarbon fuel, the combustion temperature, pressure, and reaction conditions, VOCs can significantly vary. VOCs react with the oxidants present to form various products. For instance, alkanes, upon their release with the exhaust plumes, react and primarily form OH, NO 3 , and trace amounts of Cl radicals. Alkenes, however, mainly react with the compounds in space to form OH, O 3 , NO 3 ,and Cl radicals. Alkynes and aromatics are similar, as they result in the formation of OH and Cl. Aldehydes result mainly in the formation of OH, NO 3 , Cl, and H 2 O. and composites colliding OSDs ( 11 , 38 ) Figure 1 Main Atmospheric Pollutant Emissions, their Reactions, and their Fates* (*from References: 6 , 10 , 11 , 16 , 23 , 31 , 33 , 35 − 38 , 41 − 44 , 53 ). 4. Mitigation and Pollution Prevention Techniques for Protection Against OSD In order to address the alarming and rising space pollution, governments have proposed many regulatory measures and mitigation measures, including active debris removal (ADR), to both existing spacecrafts and new ones to be launched. 6 , 10 , 46 , 47 ADR technologies or pollution prevention (source reduction) are either planned, tested, or implemented to protect the current spacecraft present in space, mostly in LEO and GEO, as well as to limit further growth of OSD, and these include utilizing green fuel instead of regular spacecraft fuel, shielding against OSD, and active debris removal (ADR). Table 2 summarizes the ADR technologies or pollution prevention (P2) methods, along with their advantages and disadvantages. As for debris of a smaller size, shielding on the satellites can be used upon unanticipated collisions. 51 This causes the debris to collide into the shielding material only, keeping the satellite parts intact. However, depending on the size of the debris and the quality of shielding material and its placement, the satellite can still be subject to damage. The International Space Station (ISS) executed a total of 29 maneuvers up to 2020 and is considered the most shielded spacecraft in space. Conclusion Even without upcoming space tourism flights, rotary space hotel construction missions, and moon mineral extraction for green energy, the current volume of orbital space debris (OSD) is alarming in terms of collision risks due to its massive size. This Review provides a summary on how OSD is generated not only in the form of tracked and untracked OSD fragments but also in the form of spacecraft exhaust atmospheric emissions that either act as OSD particles due to their large size or as O 3 decomposers and global warming contributors.

The global space industry is growing rapidly, with an increasing number of annual rocket launches. Gases and particulates are emitted by rockets directly into the middle and upper atmosphere, where the protective ozone layer resides. These emissions have been shown to damage ozone - highlighting the need for proper management of the upper atmosphere environment. We summarise the emission byproducts from rocket launches and discuss their involvement in chemical and radiative processes in the stratosphere, along with potential implications for the ozone layer due to an anticipated increase in rocket launch emissions in the future. We then present a potential vision for sustainable launches, including tractable pathways for both the aerospace industry and the ozone research community. We canvass international and domestic environmental regulation to consider how existing frameworks might be applied to rocket launches. We further identify gaps in aerospace industry practice where cooperation with environmental management and atmospheric science fields could lead to best-practise outcomes.

Hybrid rocket engines (HREs) are increasingly considered for space transportation due to their inherent safety, cost-effectiveness, and operational flexibility. However, their diffusion flame structure promotes soot formation, leading to potentially significant emissions of black carbon (BC) directly into the stratosphere. This review provides a comprehensive analysis of soot formation and evolution in hybrid rocket combustion, covering fuel pyrolysis, polycyclic aromatic hydrocarbon (PAH) growth, particle nucleation, surface growth, and oxidation processes. The physico-chemical properties and nanostructural evolution of soot are discussed in relation to combustion conditions typical of HREs. Particular emphasis is placed on the environmental and climatic implications of BC emissions, including radiative forcing, atmospheric lifetime, and heterogeneous chemical interactions. Existing diagnostic techniques for soot measurement are critically assessed, highlighting their limitations under the extreme conditions of rocket exhaust plumes. A key outcome of this review is the identification of a major knowledge gap: although preliminary experimental emission-index measurements for HRE soot have recently become available, the database remains extremely limited, fuel- and configuration-specific, and not yet supported by standardised diagnostic protocols. Addressing this gap is essential for accurate environmental impact assessments and for the development of sustainable propulsion technologies.

The study of chemical releases into the ionosphere is crucial for understanding ionospheric dynamics and managing space environmental effects. In this work, we investigate the impact of rocket exhaust emissions, particularly CO2 and H2O, on electron density in the ionosphere. To accurately capture the Te‐dependent chemical and transport processes, we develop a TIE‐GCM–based deep neural network (DNN) inversion model that infers diffusion and reaction coefficients directly from reconstructed electron density. Using this framework, continuous rocket exhaust releases are modeled as a series of point sources along the launch trajectory, enabling realistic simulations of the spatial and temporal evolution of H2O and CO2 diffusion and the resulting electron density depletion. Our results demonstrate that rocket‐released chemicals induce pronounced “electron holes” in the F‐layer, with the DNN inversion model effectively capturing the temperature‐sensitive chemical responses that are often underestimated by empirical models. This approach not only enhances the predictive accuracy of ionospheric electron density variations but also provides a robust framework for studying coupled chemical‐dynamical processes in the near‐Earth space environment.

Increasing rocket launch rates coincide with growing concerns around climate change and pollution. Few prior efforts have attempted to assess the long-term environmental impacts of rocket launches, and those that did, primarily during the US Space Shuttle program, voiced concerns about HCl depositions from solid rocket motors. Despite solid rocket motors making up a small fraction of the market today, their HCl depositions can result in environmental acidification which disrupts food chains and destabilizes ecosystems. Modeling these effects holds value as some regions are more resilient to acidification than others. This work details a qualitative model which uses a small, readily available collection of data inputs, allowing the model to cover the majority of the continental United States. The results depict regions of resiliency/vulnerability to soil acidification relative to one another. Leveraging studies in adjacent fields (e.g., acid rain) aids in discerning what effects these regions would experience. A lack of information regarding the long-term impacts of acidification limits the scope of this effort. However, the qualitative results can still aid in guiding launch site selection processes.