Intro ESA

Intro ESA Green Agenda

• Andrea Vena (ESA)

Forecasting re-entry traffic and single events

• Silvia Sanvido (IMS Space Consultancy)

Nowadays the space debris mitigation paradigm implies that what goes up to low Earth orbit must come down. Years of research have focused on concepts to make objects fall apart when they re-enter the Earth's atmosphere, so called design for demise, but surprisingly little is known on the type, amount, and sizes of small articles created in the process. This presentation is aimed to provide an overview of the methods commonly used, and associated data available, in forecasting future space traffic. This is commonly done to forecast the evolution of the space debris environment and as a side effect include the expected number of re-entry events. In addition, some upcoming re-entry events will be observable, and community feedback is sought on opportunities to directly address questions related to atmospheric pollution.

Meteors and the natural input of material into Earth's atmosphere

• Daniel Kastinen (Swedish Institute of Space Physics)

In this talk I will briefly cover what we know about the natural input of material into the Earth's atmosphere as well as how to measure and model the meteor phenomena that occurs during this input. This overview will of course not be exhaustive but will aim to provide context to the topics at hand.

Significance of the anthropogenic mass influx into Earth’s atmosphere compared to the natural influx

• Leonard Schulz (TU Braunschweig, IGEP)

The surge in space travel, especially due to the implementation of satellite mega-constellations for global internet requires mitigation strategies to counteract the increasing problem of orbital space debris. The common strategy for low Earth orbit (LEO) objects is to ensure their reentry into Earth’s atmosphere, where they ablate and burn up in the atmosphere. Due to the ever increasing launch mass into LEO, this raises the question of the significance of this anthropogenic injection compared to natural, meteoric sources, which provide a constant flow of cosmic dust and larger meteoroids into Earth’s atmosphere. A comparison of the two sources shows, that already in 2019 the anthropogenic mass input has been significant (2.8%) compared to the natural input. This number will only rise in the future due to the ongoing implementation of satellite mega-constellations. More than 5000 satellites are in orbit right now with more than 100000 proposed satellites. Considering a worst-case scenario, the injection of metals could increase to up to 90%, aerosol injection up to 94%. As the material is mainly injected into mesosphere heights, possible influences on mesospheric and even stratospheric chemistry, with effects on the ozone layer, cloud formation or the climate are thinkable. Therefore, further study and precautions are necessary, in order to protect our atmosphere from yet another human-made influence.

A growing injection of human-made materials into the high Earth’s atmosphere due to the re-entry of artificial space objects

• Carmen Pardini (ISTI-CNR)

During the last 15 years there has been an increasing number of launches, involving private actors, emerging countries and the transition to multi-object payloads. The number of operational satellites is expected to increase tenfold over the next decade, thereby also leading to a significant increase in the number of orbital launches. All types of re-entries of artificial space objects, either uncontrolled, semi-controlled or controlled, are responsible for the release of metals and particulate into the high atmosphere. Just to give an example, during the last year, up to December 4, 2023, the mass of human-made orbital objects that re-entered the Earth’s atmosphere and fragmented at high altitude was on the order of 600 metric tons. Of these, nearly 36% was associated with large (Radar Cross-Section: RCS > 1 m2) intact objects (7% with spacecraft and 29% with rocket bodies) re-entered without control. About 5% of the returned mass was instead concentrated in medium (0.1 < RCS < 1 m2) intact objects, and nearly 3% in large orbital debris (mission related objects and fragments), still re-entered uncontrolled. Controlled re-entries of spacecraft accounted for a total returned mass of approximately 130 metric tons, 80 of which disintegrated into the upper atmosphere. The remaining 50 metric tons survived re-entry and reached the ground intact. Therefore, based on the estimated mass that might have disintegrated, controlled spacecraft re-entries were likely responsible for 13% of the mass subject to fragmentation. However, the greatest amount of re-entering mass was due to some 60 launches of Falcon 9, put in low Earth orbit and mostly deorbited within a few hours. With a mass around 4 metric tons each, these actually accounted for a contribution of nearly 43% to the artificial returned mass disintegrating at high altitude in 2023. Finally, considering that between 5% and 30% of the mass of objects not designed to survive re-entry may reach the ground in the form of macroscopic fragments, the human-made mass released into the atmosphere in 2023 could range between 420 and 570 metric tons. This presentation will review the evolution of the artificial mass re-entered into the Earth’s atmosphere during the last 14 years, starting in 2010, highlighting the significant increase observed over the years, both for uncontrolled re-entries and for the increasing number of orbital launches, especially those of the US rocket Falcon 9.

Developing satellite megaconstellation emission inventories to determine the impact on stratospheric ozone and climate

• Connor Barker (University College London)

In just three years since 2019, satellite megaconstellations have grown to comprise 69% of the reported 8763 satellites in orbit, with an additional 530,000 megaconstellation satellites proposed. These megaconstellations have driven surges in rocket launches and re-entry destruction of spent satellites, contributing to large increases in anthropogenic emissions throughout all atmospheric layers. Despite the increased emissions, the potential environmental impacts of satellite megaconstellations remain uncharacterized and unregulated. Here we calculate 3D, hourly-resolved emissions of the dominant pollutants from megaconstellation and non-megaconstellation rocket launches and re-entries starting with 2020 to determine the impact of satellite megaconstellations on climate and stratospheric ozone. The pollutants include black carbon particles, nitrogen oxides (NO$_\text{x}$), water vapour, carbon monoxide, alumina particles (Al$_\text{2}$O$_\text{3}$) and chlorine species from rocket launches and NO$_\text{x}$ and Al$_\text{2}$O$_\text{3}$ from re-entries. Online repositories are used to compile information on all objects re-entering Earth’s atmosphere from above 50 km in 2020-2022, including spacecraft, rocket stages, fairings, and components from orbital and suborbital launches. The object class (core or upper stages, payload) and object reusability are used to define the chemical composition and mass ablation profile of each re-entering object. Where geolocation data is not available, geographic coordinates are randomly assigned with latitude bounded by the orbital inclination. The anthropogenic mass influx of Al$_\text{2}$O$_\text{3}$ from object re-entry in 2020 is calculated to be 0.62 Gg (1 Gg = 1000 tonnes), which is more than twice both the estimated anthropogenic and natural meteoritic injections in 2019. Over 85% of megaconstellation satellites decay within 2 years, and as a result megaconstellation re-entries have already grown to contribute 10% of the anthropogenic Al$_\text{2}$O$_\text{3}$ object re-entry emissions in 2020. The 2021-2022 megaconstellation contribution will be determined and is expected to dramatically increase as the large number of recently launched megaconstellation satellites re-enter the atmosphere. In addition, spacecraft and rocket re-entries led to a calculated mass influx of 2.70 Gg of NO$_\text{x}$ in 2020. This is an increase of 42% since 2019, with megaconstellation missions accounting for 9% of these NO$_\text{x}$ emissions. The megaconstellation emission inventories will be implemented into the 3D GEOS-Chem atmospheric chemistry transport model to simulate the impacts of megaconstellations on the ozone layer and climate. Large uncertainties remain in the size distribution, mass, and optical properties of Al$_\text{2}$O$_\text{3}$ released during object ablation, and the mass of Al$_\text{2}$O$_\text{3}$ and NO$_\text{x}$ released during controlled re-entry of reusable rocket stages and capsules. Further research in these areas would increase the accuracy of the simulation, helping to inform future megaconstellation regulation.

Potential influence of a formidable space tourism industry on stratospheric ozone and climate

• Eloise Marais (UCL Department of Geography)

The billionaire space tourism launches by Virgin Galactic, Blue Origin and SpaceX in 2021 demonstrated the potential for a future space tourism industry. All these offerings produce chemical by-products during launch and re-entry that deplete stratospheric ozone and alter climate. We modelled the environmental impact that could result from sustained (3 years) rocket launches from a plausible future space tourism industry using the GEOS-Chem chemical transport model coupled to a radiative transfer model. The vertically resolved emissions inventory we constructed was based on the location and launch profiles of the demonstration missions and assumed daily suborbital launches by Virgin Galactic and Blue Origin and weekly orbital launches by SpaceX. All launches are in the northern hemisphere, so ozone loss from re-entry NOx emissions peaks in the springtime Arctic. According to GEOS-Chem, the most severe ozone loss of ~5 ppbv is in the upper stratosphere (~5 hPa) and accounts for almost 10% of the repair that has resulted from the global Montreal Protocol ban on Earth-bound ozone depleting substances. The global mean top-of-atmosphere radiative forcing due to black carbon emissions from SpaceX and Virgin Galactic flights is 3.4 mW m-2, which is ~3% of global radiative forcing of all BC sources. This is far greater than the contribution of these rocket launches to total global BC emissions of ~0.01%, as radiative forcing per mass unit emissions is ~500 times greater than that of Earth-bound sources. Since 2021, many more space tourism companies have been established. Regulation needs to be established to mitigate harm to the ozone layer and climate that are very sensitive to space tourism emissions.

Development of a tool for calculating rocket emissions

• Tinus Breitinger
• Jan-Steffen Fischer (University of Stuttgart, Institute of Space Systems)

The number of rocket launches reached a new record in 2023 for the third year in a row. At the same time, humanity must take care not to destroy the foundations of life on Earth that have enabled it to develop. In order to provide climate and ozone models with data sets on emission profiles, a tool is being developed that calculates the emissions from rocket launches and re-entries of upper stages and assigns them to a place and time based on launch and re-entry trajectories. Depending on the selected propellants and structural material, this enables the user to estimate the environmental impact of their activities

Metals from spacecraft reentry in stratospheric aerosol particles

• Daniel Murphy (NOAA)

We measured metals that vaporized during spacecraft reentries in stratospheric sulfuric acid particles. Over 20 elements from reentry were detected and were present in ratios consistent with alloys used in spacecraft. The mass of lithium, aluminum, copper, and lead from the reentry of spacecraft was found to exceed the cosmic dust influx of those metals. About 10% of stratospheric sulfuric acid particles larger than 120 nm in diameter contain aluminum and other elements from spacecraft reentry. I will show these results and discuss why we are confident that the metals come from vaporization rather than direct production of tiny particles during reentry. The distribution of the metals provides information on coagulation and mixing in the mesosphere. Finally, I will discuss in general terms some of the possible impacts on the stratosphere.

The impact of meteoritic material and space debris on tropospheric and stratospheric cloud formation

• Daniel Cziczo (Purdue University)

The ablation products of meteoroids are incorporated into aqueous sulfuric acid and these have been measured in stratospheric particles. More recently it has been shown that metals from the ablation of satellites and upper-stage are also incorporated into aqueous stratospheric sulfuric acid particles. These particles have the potential to act as the ice nuclei upon which polar stratospheric and upper tropospheric cirrus clouds form. This is atmospherically significant because polar stratospheric clouds represent sites significant to ozone chemistry. Moreover, cirrus clouds are among the greatest uncertainty in our current understanding of climate change. This presentation will discuss what is known from laboratory and field measurements of ice cloud formation as well as potential future studies to better define ice nucleation on these particles.

Byproducts of space debris upon atmospheric reentry: the case of Aluminum

• José Pedro Ferreira (University of Southern California)

The number of orbiting satellites has increased significantly in an unrestricted and unregulated manner over the last decades, threatening the sustainable access to space. This trend is expected to continue with ongoing plans from the commercial space sector to build mega-constellations of microsatellites in spite of numerous claims of skepticism concerning its impact on ground- and space-based scientific assets. While it is widely understood that most pieces of debris will completely burn during reentry, the effect of spacecraft demise on Earth’s atmosphere has only been lightly studied and the long-term impact remains unknown with possible consequences to the ozone layer. This research presents a first-order approximation on the anthropogenic injection of metals through mesospheric reentry of spacecraft, based on key components driving the pollution footprint such as Aluminum. Molecular Dynamics simulations are used to resolve the particle size of the oxidation reaction, quantifying byproducts from thermal ablation. Forecasts are appreciated so as to extrapolate the medium- to long-term influx at the top of the atmosphere.

Global Modelling of Space Debris Impacts in the Atmosphere

• John Plane (University of Leeds)

The ablation of meteoroids entering a planetary atmosphere is the critical process which produces layers of metal atoms and ions, as well as the meteoric smoke particles which act as condensation nuclei for middle atmospheric clouds. Ablation has been modelled in the past by coupling the classical equations of meteor physics to a thermodynamic model of a high temperature silicate melt, and assuming Langmuir evaporation of the constituent elements into a vacuum. A current example of such a model is the Chemical Ablation Model (CABMOD), developed at the University of Leeds. CABMOD successfully predicts the differential ablation which is inferred from the relative abundances of the layers of Na, Fe and Ca atoms in the terrestrial mesosphere, and the time-resolved variation of radar head echoes. The underlying assumptions of CABMOD have been tested using the Meteoric Ablation Simulator (MASI) developed at Leeds. In this apparatus, meteoritic analogues of cosmic dust are flash heated to over 2800 K in a few seconds, simulating the particle heating profile that would be experienced by a meteoroid of specified mass, entry angle and velocity would experience. The evaporation of metals is measured in real time by time-resolved laser induced fluorescence spectroscopy. In this presentation I will describe the development of the CABMOD model, and how it might be developed to treat the ablation of particles larger than a few hundred microns in size. I will then discuss the requirements for global modelling of the evolution, transport and chemical impacts of space debris ablation products. In the past we have used a 3-D chemistry-climate model to simulate the transport and deposition of plutonium-238 oxide nanoparticles formed after the ablation of a power unit in the upper stratosphere (~11°S) in 1964. The model reproduces both the observed hemispheric asymmetry and time scale of Pu-238 deposition. More recently we have used the Whole Atmosphere Community Climate Model (WACCM), coupled with a sectional aerosol model, to study the transport of meteoric smoke particles from the upper mesosphere to the surface, including the processing of these particles in the stratosphere. Models of this type can be used to assess the likely atmospheric impacts of increased space debris re-entry over the next few decades.

Modeling the impacts of launch and orbital debris re-entry emissions: Initial findings and need for observational constraints

• Gavin Schmidt (NASA)

The large-scale impacts of emissions from increasing numbers of launches to Low Earth Orbit (LEO) can be robustly modeled in high-top Earth System Models with interactive composition. Emissions vary as a function of fuel type used and impacts scale with the projected launch rate per year. For plausible values of rocket engine emission parameters, scenarios with ~1000 launches/yr, stratospheric temperature, humidity and ozone impacts are detectable, and at a conceivable 10,000 launches/yr, impacts are very significant. The dominant term regardless of fuel type is likely to be the impact of black carbon (soot) emissions which are poorly understood. Impacts of anticipated increases of re-entering orbital debris associated with large LEO constellations, can also be calculated within these models and will depend on the expected particle flux, composition and size distribution, interactions with the background sulfate layer, and substrate suitability for heterogenous chemistry. Direct radiative forcing from these aerosols will likely be small, but indirect effects on ozone could be significant. Better quantification of these effects will require constraints on plausible reentry scenarios, rocket plume chemistry and reentry vaporization debris characterization, which might be derived from lab experiments, remote sensing, and in situ sampling.

Atmospheric Impact of Spacecraft Demise: Results of the ESA ARA Project

• Matthias Nützel (DLR & Ludwig-Maximilians-Universität München)

As part of the ESA-funded Atmospheric Re-entry Assessment (ARA) project (2016 to 2019) we assessed the long-term atmospheric and radiative effects of spacecraft re-entries using detailed global emission inventories for two spacecraft re-entry scenarios (a nominal and a high emission scenarios) in a state-of-the-art global climate model. The spacecraft re-entries cause ozone depletion in the upper stratosphere and in the polar mesosphere due to NO$_{x}$ emissions and heterogeneous reactions on Al$_{2}$O$_{3}$ and TiO$_{2}$ particles. However, the change in ozone is only $−$2.1$\times$10$^{-5}$ % (high emission scenario), which is a factor of 800 smaller than that of historical rocket launchers. Furthermore, we estimate a global mean near-surface temperature change by using the non-linear climate−chemistry response model AirClim, assuming constant spacecraft re-entry frequencies for each scenario between 2017 and 2100. The re-entries cause global warming of climate mainly through changes of ozone and through H$_{2}$O emission, but the calculated surface temperature change amounts to only 220$\times$10$^{-9}$ K for the high emission scenario. Overall, the warming calculated for our re-entry scenarios is much smaller than that caused by other anthropogenic emission sources such as rocket launchers and aviation given the much lower relative emission strength in our re-entry scenarios. Many challenges are remaining related to assessing the atmospheric and climate effects of space transport. Thus, we discuss open issues for chemistry−climate modelling and emission datasets related to space transport.

Accelerating regional and global warming rates from reducing anthropogenic tropospheric aerosols & increasing debates around intentional stratospheric aerosol injection

• Leon Simons (Club of Rome NL)

As emissions and atmospheric concentrations of greenhouse gases have been increasing over the past decades, aerosol emissions have stabilized and subsequently largely decreased in most areas of the world. This has resulted in a growing rate of both regional and global net forcing increase. This correlates with stronger regional brightening and warming, notably over the European continent, which has brightened (less solar radiation reflected to space) by about +15 W/m². Reductions in aerosols are a result of clean air regulations, enforcement and compliance. In 2015 strict regional regulations on ship sulfur fuel content came into effect over Emission Control Areas over the North Sea and around North America, reducing maximum sulfur fuel content from 1 to 0.1% January 1st 2020 global sulfur fuel content regulation from the International Maritime Organisation came into effect, reducing maximum sulfur fuel content from 3.5 to 0.5%. There is strong correlation between areas of active shipping and increased regional Absorbed Solar Radiation from NASA CERES (Clouds and the Earth's Radiant Energy System) satellite observations and increasing Sea Surface Temperatures. The rate of net radiative forcing increase coincides with an increase in Earth's Energy Imbalance from both satellite and in-situ assessments. There is a preliminary signal of an increased rate of global surface air temperature increase, which is more clear when taking into account ENSO cycles. This is expected to become more apparent with the current El Niño and in case of a positive Pacific Decadal Oscillation. Global warming and the effects thereof are becoming more apparent, while there is no clear sign of a decrease in greenhouse gas emissions.This has led some to argue in favor of intentional emissions of aerosols in both the troposphere and the stratosphere. The loading of stratospheric aerosols to achieve a given cooling effects is expected to be much less than for tropospheric cooling with aerosols and aerosol-cloud interactions, as indicated by inadvertent experiments, including the 1991 Mount Pinatubo volcano eruption injecting ~30 Tg of aerosols into the stratosphere.

Interdisciplinary Assessment of Space Technology's Impact on the Earth's Atmosphere and Arctic Cryosphere: from modelling to regulating

• Elena Cirkovic (Aarhus University)
• Vitali Braun (ESA)
• Hannakaisa Lindqvist (University of Helsinki)

In the Arctic, the carbon cycle is intricately linked to the cryosphere – the frozen water part of the Earth system, including ice, snow, and frost. The seasonal freeze-thaw cycles of the soil significantly influence natural methane emissions, especially from wetlands. During the thawing season, previously frozen organic matter decomposes, releasing methane, a potent greenhouse gas. Methane craters are manifestations of this process. They are formed when accumulated methane gas, trapped under the frozen ground, explosively releases as the ground thaws. This phenomenon is becoming more common due to the warming climate, which accelerates permafrost thawing. As permafrost thaws, more organic matter is exposed to decomposition, potentially releasing large amounts of methane into the atmosphere. Earth-observing satellites provide crucial data for research on methane emissions and other processes resulting from climate change in the Arctic and provide important data for regions that are difficult to access. However, the rapid increase of the deployment of space technology into Earth orbital environments requires a life-cycle assessment from an interdisciplinary perspective, for a better understanding of the impact of outer space technology on atmospheric pollution. In this paper we address these complex contradictions where we look at the useful aspects of EO data in the Arctic region, and at the same time “close the loop” by addressing how spacecraft materials and systems do/could affect the atmosphere during the objects entire life-cycle, and including re-entry. In this paper we apply interdisciplinary methodology combining engineering, atmospheric physics, and law in order to address two issues: a. the lack of data and models for a better understanding of the exact impact of space technology on the Earth’s atmosphere and the Earth System as a whole; and b. the need for more specific and comprehensive regulations of outer space activities that directly address these unique as well as emergent and/or accelerating challenges. While existing legal frameworks provide a basis for regulating the environmental impacts of space industry activities, the lack of precise data, to date, also causes vagueness in international and national laws. The unique of environmental challenges of space industry activities require specific regulations to address its impact, as well as novel and ongoing interpretations of existing laws. The paper is divided as follows. First section looks at the up-to date research on the impact of spacecraft on the Earth’s atmosphere. Second section focuses on the Arctic region and specifically the impact of greenhouse gas emissions on accelerating climate change and deglaciation. It gives a detailed account on the life cycle and circular nature of the relationship between space technology (so-called “from cradle to grave” life cycle) and the Earth System, and its positive and negative impact on the Arctic. In the third section we discuss how ongoing research as well as existing data need to be interpreted in the existing legal regimes; not exclusively: outer space law, environmental laws, national space legislation and aviation law. This section provides some suggestions for how new regulation could be more precise, as well as interpret existing legal regimes which are applicable to these challenges.

ATV-1 Re-entry airborne observation campaign

• Jason Hatton (ESA)

Exploring composition and dynamics of the middle atmosphere with ICON-ART and CAIRT

• Miriam Sinnhuber (Karlsruher Institut für Technologie)

In this talk, we will provide a short summary of the capacities of the composition-climate model ICON-ART and the proposed Infra-Red Tomography instrument CAIRT to investigate middle atmosphere composition, and how they can be utilized to analyze the impact of spacecraft re-entry. ICON-ART is a composition-climate model combining the aerosol, radiation and trace gas module ART developed at KIT with the numerical weather prediction and climate model ICON developed by the German Weather Service DWD and the MPI-M. ICON is defined by its icosahedral-triangular grid structure with a standard horizontal resolution of 80/160 km globally for climate simulations, 13 km for weather prediction. Additionally, regional refinements down to one km are possible. The model top is at 75 km in the standard, at 150 km in the “upper atmosphere” setup. ART provides aerosols, PSCs as well as different solutions for atmospheric chemistry ranging from simple tracer lifetime approaches to a full consideration of atmospheric chemistry using the very flexible MECCA chemistry solver. CAIRT is one of two candidate missions for ESAs Earth Explorer 11, currently undergoing Phase A studies. An IR limb imaging instrument, CAIRT will simultaneously observe the atmosphere from the upper troposphere to the lower thermosphere, providing a 3D-view of temperature, a large number of trace gases as well as aerosol properties.

Lidar measurements of metal atoms in the middle atmosphere: Plans for detection of space debris impact

• Michael Gerding (Leibniz Institute of Atmospheric Physics)

The middle atmosphere between about 80 km and more than 100 km altitude is well known for a layer of metal atoms like sodium, iron, nickel, calcium, etc. The metal layer is mostly formed by ablating meteoroids, which inject about 30 tons per day of cosmic material into the atmosphere. These metal atoms have been observed for decades, first by twilight spectrometry and later by resonance lidar. Thus, the natural variability and height distribution of most of these metals are well understood. Other species have rarely been observed so far because their natural abundances or backscatter cross-sections are very low. Until now, the anthropogenic contribution to the material entering the atmosphere from space, namely re-entering satellites, has been small compared to the natural source. But the composition of space debris is much different from that of meteoroids, with a higher fraction of, e.g., Al and Ni. Given the expected increase in space debris, this may alter the composition of the metal layers and enable the detection of elements that are so far invisible to ground-based lidars. We will give an overview of our plans for new and continuous observations of the mesospheric metal layer.

Draco

• Alex Rosenbaum

DRACO (Destructive Re-entry Assessment Container ObjecT) is a one of a kind mission aiming at understanding better the demisability of spacecrafts. The mission objectives can be summarized as: - Demonstrating the break-up process of a spacecraft during re-entry to extrapolate ground-test to flight. - Establishing an understanding by recording the physics of destructive aerothermal break-ups. - Testing early fragmentation design for demise (D4D) techniques. In this presentation an overview of DRACO mission will be discussed, going through the mission architecture, as well as the current system design.

Application of all-sky meteor systems AMOS for re-entry physics analysis and analysis of the negative effects on the environment

• Jiří Šilha (Comenius University in Bratislava, Astros Solutions s.r.o.)

AMOS, the All-sky Meteor Orbit System, is a system dedicated to automatic detection and orbit determination of meteors. Although the primary objects of interest are the meteors, AMOS is also suitable for the observation of re-entry events. The network offers the opportunity to observe re-entry events simultaneously from different locations, which is crucial for the trajectory determination of the re-entering object. In the last four years, AMOS systems have detected by during their autonomous detection mode four different re-entry events, each observed simultaneously from at least two different locations, providing us with great opportunity for data reduction, event modeling and methods validation. In 2020 we have captured in detail the re-entry of CZ-3B above the Hawaiian Islands. In December 2021 a Starlink satellite’s re-entry has been detected by AMOS cameras at the Canary Islands. In March 2023 AMOS cameras in Australia detected very slow object moving across the sky. By comparing this event’s time with predicted re-entry times reported by Space-Track.org, we have identified the smallsat CIRIS (University of Utah) as a possible candidate. In June 2023 CZ-2D upper stage has been detected by AMOS cameras situated in Slovakia. The ground track of the objects passed through Slovakia, Poland, and Baltic Sea. Satellites, rocket upper stages and space debris are primarily made from some kind of an aluminum alloy. The interaction with our atmosphere during the re-entry causes the object to ablate, which leads to the release of aluminum and production of aluminum oxide, also known as alumina, which can trigger further unexplored side effects in the Earth’s atmosphere, including the potential damage of the ozone layer. Optical observations using the all-sky meteor system in combination with the emission spectra of the ablating re-entry fragments captured by AMOS-Spec spectrographs can provide us with unique data which could potentially be used to assess the amount of aluminum oxides and aluminum atoms released during the observed re-entry event. Such analyses could help constrain the negative effects of re-entries on our environment. In our technical presentation we will discuss the current status of the event reconstruction for CZ-3B upper stage, introduce the other three events detected by AMOS systems and discuss the potential of AMOS observations application to tackle the problem of ozone depletion due to satellites re-entries.

What do we know about the chemistry of spacecraft constituent metals in the Lower Mesospehere-Upper Stratosphere?

• Juan Carlos Gómez Martín (Instituto de Astrofisica de Andalucía IAA-CSIC)

A large number of low earth orbit satellites are projected in the coming decades, which has led to concerns about environmental impacts of demised spacecraft. The current flux of anthropogenic aluminium vapours entering the Earth’s atmosphere is estimated to be already 10 times larger than the natural flux from meteoroids. Metals ablated from meteoroids between 80 and 110 km react with atmospheric constituents in the mesosphere forming meteor smoke particles, which are transported by the global circulation to the stratosphere, where they entrain sulfuric acid aerosols and modify their properties. Metals ablated from demised spacecraft at ~60 km have a similar fate: Recent aircraft-based measurements show that 10% of stratospheric aerosols contain metals from re-entering satellites and rocket stages. In this presentation I will give an overview of what we know about the gas-phase chemistry of spacecraft-relevant metals in the lower mesosphere-stratosphere. Based on this incomplete knowledge, I will speculate about the possible pathways of anthropogenic metals towards stratospheric aerosol and I will highlight uncertainties and experimental/theoretical work that needs to be carried out in order to address them.

Shooting stars: can their understanding provide insights to spacecraft re-entry atmospheric effects?

• Elias Chatzitheodoridis (Visiting Researcher at ESA/ESTEC, Prof. at National Technical University of Athens)

The interaction of the spacecraft material with the atmospheric gases during re-entry is getting attention because of the ever-increasing frequency of spacecraft activity in Earth’s atmosphere. Atmospheric drag and aerodynamic heating are the reason for intense friction of the spacecraft front surface and the atmosphere, inducing ultra-high temperatures and pressures because of the ultrasonic entry speeds (7–8 km/s from LEO) and occurring at about 100 km above surface. Spacecraft demise due to ablation of material is induced by the high temperatures and plasma is also formed. When plasma cools it emits in the UV/Vis/NIR spectral range. Depending on the applied thermal protection systems, ablation of different materials is under a controlled sublimation process, however space debris are mostly of metals. The same process is observed for the atmospheric entry of meteors (shooting stars), but meteors exceed entry speeds of 20 km/s. There is adequate amount of research that reports shooting star events. Spectroscopic data from the bright teils of meteors constitute chemical signatures of their chemistry in interaction with the atmosphere. Meteor studies are more difficult compared to spacecraft because meteors often have an unknown chemical composition, while variable degree of mineral erosion occurs. For this work, we are taking advantage the of accumulated knowledge from meteor spectra and from multiple experiments we have performed on natural materials (i.e., chondrite and Lunar meteorites, pure mineral phases). We simulate entry conditions using laser ablation with high-power pulsed lasers, with most frequently used a Q-switched nano-pulsed Nd:YAG laser at 1064 nm. Here we report on the sizes and textures of debris, their chemical changes, and the chemical effects on the atmosphere. Mineral debris are melts or fragments often with non-stoichiometric compositions, they can form peculiar alloy compositions, and their surfaces are reactive due to the formation of free tangling chemical bonds as well as the formation of metal superoxides. These, in reaction with air humidity form reactive oxygen species (ROS) and perchlorates, and free radicals such as hydroxyls radicals (•OH). Metal superoxides react exothermically, producing hydrogen peroxide and oxygen gas in a highly explosive reaction in higher concentrations, increasing the heat. We report on all these phenomena, and on the highly toxic and reactive oxygen species (ROS) that can concentrate in clouds and then drop as highly toxic and reactive rain.

Assessing Demise Behaviour of CubeSat Components with Plasma Wind Tunnel Experiments

• Clemens Felix Kaiser (University of Stuttgart, Institute of Space Systems)

With increasing presence of small satellites in Low Earth Orbit, investigating their re-entry demise is crucial for the future sustainability of space utilization. This relates not only to the risk of ground impacts of residual components but also to the emission of aerosols and gases in the upper layers of the atmosphere. The SOURCE PWK project, funded by the German Aerospace Center (DLR) and carried out by the University of Stuttgart’s Institute of Space Systems (IRS) aims to investigate the demise behaviour of CubeSats. The investigation employs both numerical demise simulations of the CubeSat mission SOURCE (Stuttgart Operated University Research CubeSat for Evaluation and Education) and plasma wind tunnel (PWT) experiments on its critical components. SOURCE is a 3U+ CubeSat developed by the IRS together with the small satellite student society of the University of Stuttgart (KSat e.V.). Its mission goal, besides education and technology demonstration, is to gather in-situ measurements during the very early phase of re-entry in altitudes above approximately 130 km. This data should verify and improve existing numerical models and tools for demisability analysis of spacecraft. In preparation of the PWT experiments, numerical simulations of the demise were performed with the ESA-code SCARAB developed by the HTG GmbH. With the simulation results, critical components were identified and selected for plasma wind tunnel experiments. These include titanium threaded rods, antennas, printed circuit boards (PCBs), carbon fibre reinforced plastic (CFRP) components, cameras, magnetorquers and batteries. During the plasma wind tunnel experiments, the components are exposed to high enthalpy air plasma flows emulating the stagnation point conditions during re-entry. Three different trajectory points relevant for the demise process are selected from the numerical simulations and reconstructed in the PWT by matching enthalpy and total pressure. These trajectory points are ranging from the early re-entry phase in approximately 93 km altitude to the peak heating phase, determined with SCARAB, in approximately 80 km altitude. The demise process of the selected components in the PWT is monitored with a video camera (Sony Alpha 6400), an infrared thermal camera (FLIR A6751 SLS), a linear pyrometer (KE Technologie GmbH LP3) and thermocouples at selected points of interest. Additionally, optical emission spectroscopy (OES) in the visual and near-infrared range is performed in the stagnation point region (OceanOptics HR4 VIS-NIR). The combination of the named instruments and measurement techniques allows for a time-resolved documentation of quasi individual demise processes in which the emissions of gaseous particles and droplets can be correlated to the heating process of exposed components and materials. This work presents preliminary results of the visual observation of the demise process combined with temperature measurements and OES data for selected components.

Particle-Laden Flow Characterization in High Enthalpy Ground Testing Facilities

• Ciro Salvi (German Aerospace Center (DLR))

The Supersonic and Hypersonic Technologies Department at the German Aerospace Center (DLR) in Cologne operates the LBK test facility, composed by two arc-heated, high-enthalpy wind tunnels – named L2K and L3K – capable of simulating the heat loads encountered during atmospheric entry. The LBK is one of the European key testing facilities for Thermal Protection Systems (TPS) performances, and for components’ demisability behavior, as it can reproduce high heat flux for long testing times. The experimental characterization of materials’ and components’ during atmospheric entry requires partially significant changes to the nominal operation modes of long-duration high-enthalpy facilities. Therefore, the LBK facility was upgraded in terms of operation and measurement techniques, aimed towards flow characterization studies: it is indeed of main interest to characterize wind tunnels flows, for multiple purposes, such as to get more information about the flow field, to obtain meaningful results from test campaigns, and to gain knowledge of critical aspects about high temperature fluid-dynamics effects, since flow characterization provides meaningful interpretation tools to experimental results and flow phenomena. The experimental technique based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) was recently used to determine the L2K’s flow core’s velocity, and a study demonstrated why it cannot be used to determine flow’s temperature – contrarily to what was theorized in the past – in wind tunnels similar to L2K. The study highlighted the power of non-intrusive techniques based on spectroscopy, which are capable of measuring flow quantities without the necessity of intrusive probes, providing a big leap in the possibility of understanding such complex environments. A renewed scientific interest towards particle-laden flow modelling for Martian atmospheric entry, also requires the capability of creating particle-laden flows in high enthalpy facilities, to gain a direct insight into the uncertain behavior of particles in such conditions, and to provide experimental validation data. A high-enthalpy particle-laden flow was created this year in the L2K facility, and Particle Image Velocimetry (PIV) experimental technique was performed – for the first time in a wind tunnel of this kind – with the aim of characterizing particles’ average velocity field. The presentation is about the two mentioned recent advances in the topic of “High Enthalpy Flow Characterization”, and it brings a discussion about the experimental challenges that must be faced to provide more-and-more accurate and controlled testing environments, aimed at the development of efficient and reliable spacecrafts, satellites, and interplanetary systems.

ESTHER, a new generation shock-tube for the support of planetary entry missions

• Mario Lino da Silva (Instituto de Plasmas e Fusão Nuclear - Instituto Superior Tecnico)

ESTHER is a new state-of-the-art combustion driven shock tube developed for supporting future ESA planetary exploration missions. The facility has underwent a long development cycle which came to its term in 2019, with the completion of assembly operations and the moving to the qualification and testing phases. Key requirements for this facility, as required by ESA include performance, cleanliness, repeatability, and high-turnaround time. These are all enforced through the innovative design of the facility, tailored during its long-winded development time. The ESTHER shock-tube assembly is composed of a 47l combustion chamber driver (1.6m length, 200mm diameter) filled to an initial pressure up to 100bar with He/H2/O2 gas mixtures, and ignited using a Nd:Yag laser to a final pressure of 600bar, being the first laser-ignited facility of its kind in the world. An intermediary compression tube of 130mm diameter is connected to the combustion chamber through a diaphragm designed to burst at a predetermined pressure. The compression/acceleration tube is filled with He gas at pressures of about 0.01–1bar. The compression tube is in turn connected to the shock-tube test section (80mm diameter) through a second diaphragm designed to burst at a predetermined pressure. The shock-tube is filled with a test gas at pressures of about 0.1mbar, representative of the altitudes where planetary entries occur. The shock-wave propagates in this section at velocities that may exceed 12km/s in air, or 18km/s for lighter H2/He gases. Pressure sensor stations are located at different stages of the shock-tube, detecting the rise of pressure in the wake of the shock-wave. This allows for developing a triggering system initiating high-speed (10–100MHz rated), time-dependent spectroscopic measurements at the test-section windows (25mm diameter) of the radiation emitted and absorbed in the wake of the shockwave. A 1,000L dump tank recovers all the gases flowing in the wake of the shock-wave. The H2O liquid phase is drained off, while the remaining contaminated He mixture is evacuated by the pumping system, after which the shock-tube can be opened for cleaning operations and the replacement of the diaphragms. The facility has a set of state-of-the art spectroscopic instrumentation ranging from the VUV to the IR regions, funded by two companion contracts from ESA, allowing for the facility to provide unparalleled data for the radiation of atmospheric entry flows, allowing improved knowledge of the physical-chemical processes of atmospheric entry, and furthering the understanding of atmospheric entry science and technology.

Sustainable Space: Legal and Regulatory Aspects from a Contemporary UK viewpoint

• Nicholas Ross (Niparo Ltd., Edinburgh, U.K.)

The United Kingdom has two major pieces of domestic legislation that are related to space actives: the Outer Space Act 1986 (OSA) and the Space Industry Act 2018 (SIA). The UK has also been (self-)championing itself in the regulatory, insurance and liabilities arenas as a “space sustainability” leader. In this presentation we give a quick overview of the current legislation, discuss its strengths and weaknesses, and point towards how domestic legislation and regulation can potentially help issues involved in spacecraft disposal and re-entry.

Way forward: an interactive workshop