Space Debris Solutions
Today, most artificial moons are protected from small space debris with armor. It is impossible to provide a solar panel with armor. Instead, the panel is designed to be damage tolerant, that is, other parts of the solar panel can continue to do their job as usual while the damaged part of the panel is out.
A possibility of cleaning up the space debris is being considered. A first mission is planned by ESA in 2025. This will involve launching the space capsule ClearSpace-1 to clean up Vespa (Vega Secondary Payload Adapter), a remnant from launch VV02 of a Vega rocket with a mass of 100 kg. ClearSpace-1 has gripping arms to grab hold of Vespa in the event of a space encounter, after which they will enter the atmosphere together and burn there. For the next phase, a spacecraft capable of clearing multiple space debris objects is envisioned, and the next phase will be a spacecraft capable of clearing multiple space debris objects.
The simplest thing to do, however, is to prevent it, which is why satellites are increasingly being put into graveyard orbit where they can do no more harm, when those satellites are no longer needed. Even preferring to send a discarded satellite straight back to Earth before it falls back on its own, so that one can influence where the debris comes down.
Space Debris Monitoring
Space debris can be monitored by satellite surveillance, radar and optical detectors. Both the US Federal Space Agency (NASA) and the European Space Agency (ESA) have established space debris monitoring systems, the former in close cooperation with the US Department of Defense. The Department of Defense's space surveillance network can track objects as small as 5 cm in diameter in Earth's lower orbit and up to about 1 metre in geostationary orbit. To date, 15,000 objects have been catalogued.
ESA's Space Surveillance and Tracking (SST) programme aims to detect and predict the movement of space debris in orbit around the Earth. The data generated by SST systems can be used, among other things, to protect space-based infrastructure such as satellites and the International Space Station. SST systems use radar and telescopes to observe the sky and produce images of the objects in orbit around the Earth that they detect. If the object is already known, the existing data, concerning the current object, is updated based on the latest observations. It is then catalogued.
At the end of August 2014, a start-up collaboration between US defence giant Lockheed Martin and Australian company Electro Optic Systems was announced to build a ground-based tracking station in Western Australia and, using advanced laser and optical technology, track, find, identify and follow space debris.
Space Debris Prevention
To avoid collisions with pieces of space debris, all larger particles (1 cm or larger) are permanently tracked by responsible NASA and military observatories. If a collision course with the ISS or another manoeuvrable spacecraft is detected, this typically occurs early enough (several days in advance) for this spacecraft to initiate an evasive manoeuvre. Since the ISS always has to be returned to a slightly higher orbit anyway, this does not cost any additional fuel.
To avoid space debris, all modern rockets use an additional engine ignition to slow down the stages entering orbit again, so that sooner or later they will burn up in the atmosphere. ESA proposes to limit the duration until the re-entry of mission-related objects (MROs, see above) depending on the cross-sectional area.
For upper stages that enter high orbits and cannot generate sufficient braking momentum, at least the remnants of the propellant are used up or drained to prevent a possible explosion. In February 2021, after almost eight years of negotiations, this was made mandatory by the International Organisation for Standardisation in the ISO 20893 standard. Geostationary satellites themselves are now no longer used until their fuel supplies are completely exhausted, but are placed in a graveyard orbit with some remaining.
In order to slow down the avalanche-like increase in the number of small objects due to collisions with larger ones, it has been proposed to dispose of at least larger inactive objects. Various ideas have been proposed on how to dispose of several objects in a single, longer mission. Problematic aspects are the interaction with uncontrolled rotating objects and the large amount of support mass required for numerous orbit changes.
Space Debris Removal
The company ClearSpace.today was founded in 2018 by engineer Luc Piguet as a spin-off of the EPF Lausanne. In December 2019, the ESA Council of Ministers decided to test and carry out the removal of space debris from 2025 with the ClearSpace-1 mission. This will involve a "hunting satellite" with four mechanical arms grabbing a suitably sized piece of space debris and then plunging into the Earth's atmosphere together with the object, where they will both burn up. To this end, ESA contributed CHF 90 million to the project, which is expected to cost around CHF 120 million in total - to dispose of a single piece of debris.
On 13 February 2009, the United Nations called on all countries with activities in space to put measures in place to stop the growth of space debris in the atmosphere, so as to preserve the environment of outer space for future generations However, the problem of existing space debris is a tough nut to crack. Below an altitude of 400 kilometres above the Earth's atmosphere, space cleans itself, meaning that everything up to that altitude will fall down on its own and burn up in the atmosphere, and everything up to 1,450 kilometres will fall down within 3,000 years as an effect of the Earth's gravity.
Today, there are a number of potential solutions for cleaning up the space around us and one proposal is to build a barbed harpoon to collect the debris The idea comes from the British company Astrium and involves firing a 30-centimetre long barbed arrow at the debris objects, guiding them towards the Earth's atmosphere where they can then burn up. A similar project is Switzerland's Clean Space One, which involves building nanosatellites to seek out and collect space debris. Unfortunately, these methods only work on larger objects. In 2011, NASA began developing a strategy to shoot down space debris with lasers, but again, we're talking about something that doesn't include the smaller garbage - those up to a centimetre in diameter.
Unfortunately, there's no really good method for picking up the smaller space debris, which is a big problem in itself. The methods used now are to limit their growth, partly through rules to be followed to prevent more littering. There are certain parts of near-space where it is forbidden to dump leftover spacecraft and end-of-life satellites.
Burning up of space debris from low orbits
Lifetime at different altitudes
The pieces in low orbits are slowed down by a residual air resistance and eventually burn up in the atmosphere. At higher altitudes, air friction becomes less and less, so that larger objects from an altitude of 800 km take decades to burn up, but from an altitude of 1500 km they take several thousand years. However, the fine wires of the West Ford project, as far as they were travelling unclumped, returned from an altitude of more than 3500 km within a few years, as calculated, with the support of the Sun's radiation pressure.
As the altitudes of 800 km and 1500 km are preferred as orbits, the threat to commercial and scientific spaceflight is growing. Concepts on how to solve this problem are currently failing because of the costs involved.
Examples of partial burn-up
In the case of very large satellites and especially heat-resistant components, it can happen that they partially survive re-entry and that some fragments, sometimes very heavy, reach the earth. Examples include ROSAT with heat-resistant mirrors made of glass ceramics or the 5.9-ton Upper Atmosphere Research Satellite.
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