Space sustainability
Space sustainability aims to maintain the safety and health of the space environment, as well as planetary environments. Similar to sustainability initiatives on Earth, space sustainability seeks to use the environment of space to meet the current needs of society without compromising the needs of future generations. It usually focuses on space closest to Earth, Low Earth Orbit, since this environment is the one most used and therefore most relevant to humans. It also considers Geostationary Equatorial Orbit as this orbit is another popular choice for Earth-orbiting mission designs.
The issue of space sustainability is a new phenomenon that is gaining more attention in recent years as the launching of satellites and other space objects has increased. These launches have resulted in more space debris orbiting Earth, hindering the ability of nations to operate in the space environment while increasing the risk of a future launch-related accident that could disrupt its proper use. Space weather also acts as an outstanding factor for spacecraft failure. The current protocol for spacecraft disposal at end-of-life has, at large, not been followed in mission designs and demands extraneous amounts of time for disposal.
Precedent created through prior policy initiatives has facilitated initial mitigation of space pollution and created a foundation for space sustainability efforts. To further mitigation, international and transdisciplinary consortia have stepped forward to analyze existing operations, develop standards, and incentivize future procedures to prioritize a sustainable approach. A shift towards sustainable interactions with the space environment is growing in urgency due to the implications of climate change and increasing risk to spacecraft as time presses on.
Fundamentals
Space sustainability requires all space participants to have three consensuses. The space field should be used peacefully, jointly protect the space field from harm, and maximize space utilization through environmental, economic, and security exploration of space. These consensuses also clarify the relationship between space sustainability and international security, that states and individuals explore space for various purposes. Their reliance on space needs to be guided by rules, order, and policies and obtain more benefits without negatively affecting the space environment and space activities.However, striking an agreement remains challenging even with such demands in place. In the discussions between countries on long-term sustainability, technical improvements are given more importance than introducing and applying new legal regimes. Specifically, technical approaches to space debris have been proposed, such as debris removal. Specific data on space debris is also being explored to help study its impact on sustainability and promote further cooperation between countries.
Current state
Space sustainability comes into play to address the pressing current state of near-Earth orbits and its high amounts of orbital debris. Spacecraft collisions with orbital debris, space weather, overcrowding in low Earth orbit makes spacecraft susceptible to higher rates of failure. The current end-of-life protocol for spacecraft exacerbates the space sustainability crisis; many spacecraft are not properly disposed, which increasing the likelihood of further collisions.Orbital debris
is defined as unmanned, inoperative objects that exist in space. This orbital debris breaks down further as time progresses as a result of naturally occurring events, such as high-velocity collisions with micrometeoroids, and forced events, such as a controlled release of a launch vehicle. In LEO, these collisions can take place at speeds anywhere between an average velocity of 9 kilometers per second and 14 km/s relative to the debris and spacecraft. In GEO, however, these high-speed collisions are a much lower risk as the average relative velocity between the debris and spacecraft is typically between 0 km/s and 2.5 km/s. As of 2012, the United States Joint Space Operations Center tracked 21,000 pieces of orbital debris larger than 10 cm in Earth's nearby orbits, where 16,000 of these pieces are catalogued. Space debris can be categorized into three categories: small, medium, and large. Small debris is for pieces that are less than 10 centimeters. Medium-sized debris is for pieces larger than 10 cm, but not an entire spacecraft. Large-sized debris has no official classification, but typically refers to entire spacecraft, such as an out of use satellite or launch vehicle. It is difficult to track small-sized debris in LEO, and challenging to track small and medium-sized debris in GEO. Yet this statement is not to discount the abilities of LEO and GEO tracking capabilities, the smallest piece of tracked debris can weigh as low as ten grams. If the size of the debris prohibits it from being tracked, it also cannot be avoided by the spacecraft and does not allow the spacecraft to lower its risk of collisions. The likelihood of the Kessler syndrome, which essentially states that each collision produces more debris, grows larger as the amount of orbital debris multiplies, increasing the amount of further collisions until space cannot be used entirely.Space weather
Space weather poses a risk to satellite health, consequently, resulting in greater amounts of orbital debris. Space weather impacts satellite health in a variety of ways. Firstly, surface charging from the Sun's surface facilitates electrical discharges, damaging on-orbit electronics, posing a threat to mission failure. Single Event Upsets can also damage electronics. Dielectric charging and bulk charging can also occur, causing energy problems within the spacecraft. Additionally, at altitudes less than one thousand kilometers, atmospheric drag can increase during solar storms by increasing the altitude of the spacecraft, only adding more drag onto the spacecraft. These factors degrade performance over the spacecraft's lifetime, leaving the spacecraft more susceptible to further system and mission failures.Overcrowding
There has been a dramatic increase in the use of LEO and GEO orbits over the last sixty years since the first satellite launch in 1957. To date, there have been approximately ten thousand satellite launches, whereas only approximately 2000 are still active. These satellites can be used for a variety of purposes, which are telecommunications, navigation, weather monitoring, and exploration. Within the coming decade, companies like SpaceX are predicted to launch an additional fifteen thousand satellites into LEO and GEO orbits. Microsatellites built by universities or research organizations have also increased in popularity, contributing to the overcrowding of near earth orbits. This overcrowding of LEO and GEO orbits increases the likelihood of potential collisions among satellites and orbital debris, contributing further to the large amount of orbital debris present in space.End of life protocol
The current end of life protocol is that at the end of mission, spacecraft are either added to the graveyard orbit or at a low enough altitude that drag will allow the spacecraft to burn up upon reentry and fall back to Earth. Approximately twenty satellites are put into the graveyard orbit each year. There is no current process to return satellites to Earth after entering the graveyard orbit. The process of a spacecraft returning to Earth via drag can take between ten and one hundred years. This protocol is critical to reduce overcrowding in near-Earth orbits.Mega constellation and space debris
The impact of constellations on the space environment has also been studied, such as the probability of collisions of mega constellations in the presence of large amounts of space debris. Although studies have shown that the predictors of mega constellations are highly variable, specific information related to mega constellations is not transparent.But any catastrophic collision, as in the case of Kessler syndrome, has consequences for people and the environment. Putting this thinking into mega constellations, their existence may have potential benefits, but it will not bring adequate help to the governance of space debris. At the same time, the space debris situation cannot be underestimated or ignored because of the existence of mega constellations.
Areas
Planetary environment
Space environment
The existence of orbital debris has caused great trouble to the conduct of space activities. The development of space sustainability has not given sufficient political attention, although some warnings and discussions have made this abundantly clear. Debris management is still voluntary on the part of the state, and there are no laws mandating debris management practices, including the amount of debris to be managed. Although the UN Space Debris Mitigation Guidelines were promulgated in 2007 as an initial measure of space debris governance, there is still no broad consensus or action on further limits on space debris after that.The difficulties for individuals wishing to participate in debris management initiatives cannot be ignored. Any individual or sector desiring to participate in space debris operations needs to obtain permission from the launching state, which is difficult for the launching state to do. This is because the process of space debris management inevitably has a negative impact on other space objects, and there is a lot of subsequent liability in terms of financial consumption. Therefore, the launching state would argue that space debris management requires the joint efforts of all states. However, it is difficult to determine what actions can be taken to gain acceptance between countries.