Protecting satellites in low Earth orbit: An overview of hazards and policy solutions

Satellites in the Low Earth Orbit (LEO) environment face various hazards which threaten the long-term sustainability of the space economy. This article describes the potential dangers to satellites in LEO beyond commonly referenced orbital debris and satellite collisions, including hazards that arise from the LEO environment itself and from other anthropogenic sources such as laser interference and orbital light pollution. As the LEO economy surges in the coming decade, preventative policy such as that proposed in this article could address these risks before they become an issue and ensure that the LEO environment continues to grow sustainably.


Figure 1:
The number of active satellites orbiting Earth per year is increasing exponentially over time [1].Low Earth Orbit, where 80% of these satellites operate, encompasses all Earth-centered orbits at an altitude of 2000 km or less.
The number of active satellites in space is growing exponentially, and the vast majority of new satellites are located in LEO.From 2020 to 2021, the space industry observed an increase in active satellites by 47.4%.From 2021 to 2022, the number of active satellites increased by 43.9%.These statistics show a rapid increase in space activity as shown in Figure 1.More than 80% of the new satellites operate in LEO.LEO's fixed volume encompasses all Earth-centered orbits at an altitude of 2000 km or less, and as the number of satellites in this region increases, so does the prominence of hazards to the increasing volume of satellites.
The number of satellites in space threatens the sustainability of the environment for future use, as underscored by recent policy changes.In September of 2022, the Federal Communications Commission (FCC) adopted a "5-Year Rule" [2], which states that satellite operators must decommission and dispose of their satellites in LEO within 5 years after end of life.Prior to this regulation, operators had 25 years to dispose of their satellites [3].The difference in these time frames implies an increased effort to maintain sustainability in space.While the primary focus of this regulation is on reducing the number of satellites in space this framework will not adequately address all the risks posed to the planned volume of satellites launched in  This figure depicts the 57,000 satellites planned to launch in the coming decade on the right hand side, color coded by the companies that plan to launch detailed on the left hand side.Grey satellites depict satellites launched during previous years [5].the near future.Figure 2 depicts some of the companies launching satellites in the coming decade, with over 57,000 satellites planned.While it is evident due to the number of satellites planned to launch that collisions represent a substantial danger to objects in space [4], hazards arise from other sources as well.
This article considers hazards that exist in LEO as the result of environmental sources and anthropogenic sources.Hazards to satellites from the environment include space weather and meteoroid collisions.Hazards from other human-made sources include radio and laser communications interference, orbital light pollution, and ionizing radiation.The current policy has gaps that do not adequately address these satellite hazards as the LEO sector surges in the coming decades.Finally, preventative policy directions are presented that address gaps in existing legislation.

Environmental hazards
Dangers to satellites are inherent in the LEO environment.One of the most significant risks comes from space weather, which refers to conditions in space from solar activity.Specific high risk locations for space weather impacts, locations with more intense radiation, include the Earth's magnetic poles and the South Atlantic Anomaly [6].The interaction of these hazards can have significant impacts on spacecraft such as Single Event Upsets (SEUs), accumulating total radiation dosage, and drag.In addition to the hazards caused by space weather, meteoroids also pose a significant threat to spacecraft due to the potential of high-velocity impacts.These environmental hazards and their impact on satellite performance and longevity highlight the need for policy solutions to mitigate their effects.Because it is not possible to regulate the LEO environment itself, policy solutions must support how designers and operators of spacecraft interact with or respond to the space environment.
Space weather: Space weather, diagrammed in Figure 3, encompasses conditions resulting from solar activity and the resulting solar wind interacting with the Earth's magnetosphere, ionosphere, and thermosphere that can impact technological systems and human life.Flares, solar energetic particles, and coronal mass ejections are examples of space weather events that can cause disturbances to satellites, astronauts, and the Earth's magnetic field.These events release radiation across a wide range of wavelengths and can have near-instantaneous effects [7].Solar flares are eruptions of energy from the Sun's surface.They produce electromagnetic radiation across the spectrum, including X-rays and gamma rays.The particles produced accelerate towards the Earth at speeds near that of the speed of light.The frequency and duration of these flares may vary, although they typically follow an eleven year cycle between solar maximums; flares occur multiple times a day during a maximum and as little as approximately once per week during a minimum.Similarly, a coronal mass ejection (CME) is an ejection of magnetic fields and plasma mass from the Sun's corona into the heliosphere, often associated with solar flares.The frequency of CMEs varies with the solar cycle with three per day occurring with solar maxima and one per five days occurring during solar minima.Solar Energetic Particles (SEPs) are high energy particles that are accelerated by solar flares and CMEs.The energetic particles released during these events can damage satellite electronics, leading to temporary or permanent malfunctions.Additionally, the increased ionization of the ionosphere during these events can cause disruptions in satellite communications and navigation systems.Some regions in LEO are at higher risks of impact from space weather than others.Figure 4 from [8] shows the relationship between spacecraft altitude and latitude to the risk of experiencing surface charging, one of the impacts of spacecraft interactions with charged particles.In the case of LEO, spacecraft are at risk of this phenomenon below an altitude of 2000 km as indicated in this figure.Auroral zones are oval-shaped regions observed at the North and South poles resulting from ionization in the upper atmosphere by charged magnetospheric particles accelerated during periods of enhanced solar activity.These ovals are important features of the magnetospheric response to space weather, associated with increased electromagnetic disturbances and particle precipitation that can degrade satellite technology [9].The South Atlantic Anomaly is a large anomalous feature that extends from the East Pacific to South Africa and covers latitudes between 15 and 45°S with a minimum value of 22,500 nT near Asunción city.The weak geomagnetic field over the South Atlantic Anomaly (SAA) causes high radiation close to Earth's surface, affecting both satellite and communication systems on the ground [10].
Interactions between space weather and satellites including single event upsets, total dosage, and drag, can have various impacts on the performance and longevity of these orbiting systems.
Single event effects: Single-event effects refer to the impact of a solitary high-energy particle on electronic components, resulting in temporary or permanent changes in their behavior.Increased solar activity is correlated with an increase in non-destructive single-event upsets.Two space weather events from solar eruptions in 2012 and 2017 resulted in increased single-event upsets in satellite memory devices.The Eros B satellite detected an elevated rate of single-event upsets on two of its processing computers during periods of elevated high-energy proton flux.These anomalies occurred after X-class flares (large magnitude flares that can be up to 10 times as large as the Earth) were detected and when the 100 MeV protons flux was three orders of magnitude above the background levels [11].
Total dosage: When insulating layers of semiconductor components become ionized, trapped positive charge accumulates and affects component behavior, resulting in threshold shifts and off-state leakage currents.If the dose levels of this charge reach a critical point, the component may become defective and cause the loss of critical spacecraft systems.This effect can be exacerbated by either protons or electrons.For LEO, the biggest increase in a spacecraft's cumulative ionization dosage can be from protons in the SAA [12].This cumulative effect also degrades solar cells, decreasing the maximum power output achievable prior to the end of life [12].Additionally, the accumulation of radiation effects can also cause spacecraft optics to yellow and darken.Figure 5 shows a series of images taken by the XI-IV CubeSat over a series of 15 years that illustrate how dramatic the darkening due to radiation can be [13].Drag: Solar heating associated with higher periods of solar activity can cause atmospheric expansion and increased atmospheric density, which results in a greater atmospheric drag on LEO satellites.This can lead to accelerated decay of orbit, increased collision risk due to higher error in positioning knowledge, and uncertainty in the re-entry time and location of de-orbiting spacecraft [14].Increased atmospheric density during an unexpected geomagnetic storm is what prevented 40 Starlink satellites from reaching the appropriate altitude to exit safe mode and start orbital raining maneuvers, thus causing the satellites to reenter the atmosphere [15].
The United States' (US) National Space Weather Strategy and Action Plan released in 2019 designates three objectives for improving national preparedness to space weather effects [16].These include enhancing protection of both space and ground assets against space weather effects, developing better space weather forecasting and dissemination capabilities, and establishing policy for responding to and recovering from space weather events.While this action plan establishes a framework for addressing space weather, policy is still needed to implement its goals.

Meteoroid collisions:
Meteoroids pose a hazard to spacecraft due to high-velocity impacts that can cause mechanical damage and penetration, as well as generate plasma that can cause electrical damage.The impact character of meteoroids is different from that of space debris, with higher average collisional velocity and different bulk density.Despite the fact that larger, higher-velocity meteoroids are capable of greater destruction, impacts from smaller meteoroids are far more frequent.The smaller, more frequent impacts can cause damage to small-but still criticalcomponents such as external wire bundles [17].
Studies have mainly focused on mechanical damage, but there is growing evidence that plasma generation from higher-velocity impacts may be more damaging in some cases [18].When the meteoroid strikes, it can ionize itself and the spacecraft.This plasma can produce a strong electromagnetic pulse at broad frequency spectra and can cause catastrophic damage if the impact is near an area with low shielding or an open umbilical, and subsequent plasma oscillations can also emit significant power [19].Ground-based instruments can detect interactions between meteoroids and the Earth's atmosphere.While these instruments can detect the plasma that is formed around a micrometeor upon impact, direct measurement of the micrometeors are not possible, requiring significant modeling effort.
Current policies addressing environmental hazards focus on prevention, ensuring safe design and operation of spacecraft to mitigate the effects of these continuous threats.As spacecraft in orbit age, the effects of these hazards on the spacecraft are often increased, so designers must be mindful of end-of-life operations and disposal from the beginning.US policy for preventing disastrous consequences from these effects is based upon the Orbital Debris Mitigation Standard Practices (ODMSP), with each sector implementing these best practices through their regulating agency's policies; US civil space missions follow National Aeronautics and Space Administration (NASA) Technical Standard 8719.14, military missions must adhere to Air Force Instruction 91-202, while commercial missions follow FCC 22-74 [20]- [23].As the LEO ecosystem becomes more congested, clear and consistent guidelines are required for satellite operators to follow in the event of increased environmental activity.

Anthropogenic hazards
In addition to dangers that arise from the LEO environment itself, anthropogenic hazards, those arising from human-made objects and activity, also threaten satellites in LEO.
Radio interference: Spacecraft communicate with each other and ground stations using radio emissions, governed by the Radio Regulations.Within the United States, the Federal Communications Commission regulates spectrum allocation for commercial applications while the National Telecommunications and Information Administration (NTIA) regulates for government applications.Satellite missions are allocated specific bands of the radio spectrum, and must abide by rules governing when and how they can use spectrum.As the number of satellites continues to grow, more of this spectrum is being utilized and increasingly complicated schemes are being designed for using currently allocated bands.How these newer schemes and systems interfere with each has been an ongoing discussion for decades [24].Currently, regulations such as the LEO Equivalent Power Density Flux limits deal with concerns about interference between different satellites [25].Developments such as decreasing antenna size on GEO satellites are straining this regulation, as this increases their sensitivity, a positive development for their capabilities; but means that they are now more susceptible to the higher side lobe gain of the similarly small antennas onboard LEO satellites [26].
Independent of communications technology changes, radio interference between satellites is a growing concern as LEO usage increases exponentially due to the advent of mega-constellations such as Starlink [27].The sheer number of these satellites can easily crowd out other signals if operators are not careful with their mission design to avoid other mission's bands.In 2019, a new milestone-based process was approved for non-geosynchronous satellite constellations to prevent spectrum 'warehousing', the reservation of radio frequencies without putting them into use within a certain amount of time [28].However, even with these new measures, the resource remains finite.Researchers and regulators have explored ways of expanding spectrum use through different bands like V and W along with optical, as well as new modulation schemes.Many technologies to support these frequencies and techniques are still in development, but once they are on the market, they too could face some of the same regulatory and congestion problems the traditional bands have faced.Laser interference: Laser communications are growing in use for satellites due to their greater power efficiency, higher data rates, and narrower spectrum usage, but require finer pointing control [30].The shorter wavelength and smaller beams of laser communications contribute to their greater power efficiency, but this also means there is more energy being directed onto a single point, and a wayward satellite could point at another satellite, damaging onboard detectors they are using for missions such as Earth observation or astronomy.This is especially notable for the mega constellations like Starlink which is putting up thousands of satellites that may utilize laser communications for their inter-satellite links.This presents a much larger chance for unintentional interference with other satellite missions, as it will be the first time anyone has at scale, in both frequency of use and number of satellites, used laser communications.
Laser applications from the ground transmitting through navigable airspace must coordinate operations in the US with the Federal Aviation Administration (FAA), following FAA Order JO 7400.2K and ANSI Z136.6 "American National Standard for Safe Use of Lasers Outdoors" [31].However, space-based laser regulations remain nascent.Military space laser use is currently managed in the US through the Laser Clearinghouse (LCH) by US Space Command's Combined Space Operations Center (CSpOC) for deconfliction of military laser activities to ensure no damage occurs to spacecraft in orbit [32].Civil and commercial activities are also welcome to register their activities with the LCH, but registration of these applications is currently not required.With the growing use of laser communications, it may be advantageous to require registration of all US space-based laser activities to the LCH for deconfliction purposes.It is unclear though, given the current size of the LCH, whether or not it would be able to keep up with demand [32].Whether regulation of these activities should fall under the jurisdiction of the FCC also remains to be seen [33].
Orbital light pollution: Satellites may interfere with LEO-based optical and infrared imaging of the Earth's surface or space due to orbital light pollution from other satellites in the Field of View (FoV) of onboard cameras [34].The increase in satellite constellations in LEO also creates a hazard for optical exposures of astronomical objects of interest.As an example, the Hubble Space Telescope operates in LEO at a lower altitude than the Starlink constellations which may streak through exposures or reflect light back to the cameras on Hubble.An example of streaking from Stalink constellations is shown in Figure 7.While the threat to ground-based astronomy, known as radioastronomy, is being extensively explored [35], the threat to LEO-based science also involves the sheer number of satellites that will congest space in the near future.Many current and future satellite missions will include some form of propulsion to assist with station-keeping and collision avoidance maneuvers.Maneuvers may leave plumes and emissions which could also clog up imagery taken either from the ground or from satellites in higher orbits, as well as release potential atmospheric contaminants which are not currently regulated.For individual satellite missions, these emissions would not present much of an issue but in the case of mega-constellations, the sheer number of satellites generating emissions could be a problem for imagery.
Recently, SpaceX reached a coordination agreement with the National Science Foundation (NSF) to minimize the effect of Starlink's orbital light pollution on ground-based astronomy.They plan to reduce optical brightness of their satellites below a threshhold of 7th visual magnitude, maintain orbital elevations below 700 km, and provide information publicly about their orbits.The next generation of satellites from SpaceX will also incorporate dielectric mirror film, solar array mitigations, and black paint to minimize brightness [37].
The changes SpaceX is implementing to facilitate coordination with the ground-based astronomy community will positively impact on-orbit astronomy as well.While the agreement between SpaceX and the NSF serves as a model for coordination between the commercial satellite industry and the astronomy community, the space community has not implemented these regulations at large.Policy reflecting this agreement could improve the overall hazard of orbital light pollution.
Ionizing radiation from nuclear-powered systems: Nuclear power has been used in space systems since the early 1960s, most commonly in the form of Radioisotope Thermoelectric Generators (RTGs) [38].RTGs utilize the decay of nuclear material, usually Plutonium-238 or Americium-241, which produce heat to generate electricity.Nuclear fission reactors have also been flown to heat satellites and/or power their systems.As space systems have advanced, high power requirements have led to the development of various space nuclear applications.While the use of these technologies is currently sparse, they do present a potential hazard to both the space and Earth environment, shown in the cases of TRANSIT 5BN-3 and COSMOS 954, as an impact or explosion can spread radioactive debris in space and on Earth [39].Radioactive debris within an orbit can impact satellites within the same orbit and those nearby in a manner similar to the effects of radiation from space weather but at much higher doses.This could therefore seriously damage or completely disable these satellites.
United Nations (UN) General Assembly Resolution 47/68 Principles Relevant to the Use of Nuclear Power Sources in Outer Space outlines allowable peaceful uses of nuclear sources in space [40].Use of RTGs and nuclear reactors in the LEO environment are only allowed by this ruling after their operational mission life has ended and if they have first been in a higher orbit sufficiently long enough to decay the fission products to a reasonable safety level.With the development of the LEO commercial economy, emerging players may want to consider using nuclear sources for high power requirement applications like commercial space stations and in-space manufacturing.Under current regulations though, this is restricted and will require a concerted effort on the part of regulators and space actors to develop policies which enable these new capabilities while still maintaining safety.

Moving forward
According to the European Space Agency's (ESA) Space Environment Report 2022, the number of objects in space increased 90% since 2019, largely due to the launch of mega-constellations; this number will only get larger due to the increased demand for satellite services in areas such as telecommunications, Earth observation, and navigation [41].As the number of satellites in LEO increases, the competition for limited resources such as radio frequency spectrum and orbital space will intensify.This can result in higher costs for companies and governments seeking to launch satellites, which could hinder innovation and economic growth.Additionally, this can make it challenging for new players to enter the market, leading to a concentration of power in the hands of a few dominant players.As space becomes more crowded, it will be important to establish clear rules and regulations governing its use to avoid conflict and ensure sustainability.Space faring nations have already established frameworks for international cooperation in space, but as the use of space expands, it will be crucial to develop new agreements and mechanisms to ensure that space exploration benefits all of humanity and is not monopolized by a few dominant players.
Potential solutions: Addressing the threats posed by environmental and anthropogenic hazards in LEO will require a combined effort from both the private and public sectors to develop effective and efficient policy solutions.The recent agreement between NSF and SpaceX on limiting orbital light pollution from satellites is not only a lead for solving one part of hazard-related issues, but also a leading example of cooperation between corporate and public entities [37].In an era when every next action could threaten the sustainability of the space ecosystem, collaboration will be key to properly and effectively addressing challenges.
Most of the hazards discussed can benefit from better coordination of space system activities to prevent interference to mission requirements and objectives.A potential framework for addressing this is through Space Traffic Management (STM) [42,43].STM is based on the fact that passive location knowledge of space objects is not enough to operate safely in today's congested environment.STM requires both knowledge and coordination.Yet, the current state is merely described as Space Situational Awareness (SSA).The ability to jointly maneuver and regulate the positions of spacecraft could reduce the uncertainty and risk of current operations.Once STM is performing as described, Space Debris Management (SDM), an overlapping framework, could be integrated and developed further to ensure the long-term sustainability of the space regime.
Another debris avoidance tool is the warning system for the national defence provided by the Combined Space Operations Center (CSpOC), which is also responsible for observing more than 23,000 objects in the Earth's orbit.CSpOC is a reliable source for satellite operators to get insights into traffic management.[44] Space operators could also benefit from an increase in data acquisition and sharing.NASA's 2021 report on "Efforts to mitigate the risks posed by orbital debris" concluded that the biggest impeding factor on the way to better characterizing the debris environment is the lack of data [45].All of the hazards discussed also require better characterization to understand the full scope of the problem in the LEO environment.Knowledge of spacecraft anomalies related to environmental hazards can help spacecraft designers guard against these in future iterations of technology.Location and mission objective knowledge can help manage efforts to avoid anthropogenic hazards.Enhancing data sharing capabilities between civil, military, and commercial actors could also help coordinate activities and provide lessons learned.A challenge that could possibly be faced, however, upon implementation of the aforementioned is the confidentiality of national data and privacy issues when it comes to sharing.
To address the issue of sustainability in space, regulation should consider the importance of balancing the rights and responsibilities of all stakeholders while considering the aforementioned examples of risk.The latter includes governments, space agencies, and international organizations such as the United Nations Office for Outer Space Affairs (UNOSA).Similar to taking joint actions to meet the 17 Sustainable Development Goals (SDGs) outlined by the UN, all concerned space actors can consider sustainability in space as SDG 18 and collaborate to achieve it [46].Quantitative indicators like SDG indices could plausibly be embodied in the overall assessment of progress in maintaining sustainability of the LEO regime.This could not only bring sustainability to LEO and space as a whole but may also motivate member states to strive to achieve other SDGs.

Conclusion
Activities in LEO are crucial for driving technological innovation in many sectors, but rapid acceleration of space activities poses challenges that threaten sustainability and safety of the space environment.While policy changes are currently being implemented to address sustainability of the LEO environment through maintaining sustainable populations of spacecraft and mitigating debris, they do not sufficiently address other hazards to satellites during operation.This work discussed hazards in LEO caused by both environmental and anthropogenic sources.Environmental hazards include space weather and meteoroid collisions which may impact satellite performance and lifespan.Anthropogenic hazards include radio interference, laser communications interference, orbital light pollution, and ionizing radiation.
Current policy primarily focuses on preventing catastrophic consequences of collisions on orbit and ensuring safe spacecraft design and operation.Guidelines and standards such as the Orbital Debris Mitigation Standard Practices are in place to mitigate the effects of debris on orbit, but as the LEO space becomes more congested, clear guidelines will be necessary to navigate other hazards.
Addressing environmental and anthropogenic hazards and ensuring long-term sustanability of the space environment require comprehensive policy solutions.This work emphasizes the positive impact preventative policy may have by holistically addressing the growing volume of satellites and their associated risks as a collaboration between private and public entities.

Figure 2 :
Figure 2: This figure depicts the 57,000 satellites planned to launch in the coming decade on the right hand side, color coded by the companies that plan to launch detailed on the left hand side.Grey satellites depict satellites launched during previous years [5].

Figure 3 :
Figure 3: Diagram of Space Weather where blue lines indicate solar wind from the sun and pink lines show the Earth's magnetic field.Green lines at the North and South poles of the Earth are the Aurora oval.

Figure 4 :
Figure 4: Risk of Charging from Accelerated Particles based on Latitude and Altitude [8].

Figure 7 :
Figure 7: Picture of orbital light pollution due to a Starlink constellation, figure from [36].