FAQ: Space debris - Frequently asked questions
Q11: How do unmanned spacecraft protect themselves against space debris?
The most probable impacts are due to small space debris. One can efficiently increase the protection of an unmanned spacecraft by moving sensitive equipment away from the most probable impact direction, and/or by covering sensitive parts of the spacecraft with protective fabric layers (the 'bullet-proof vest' approach).
Such measures can significantly increase the survivability of a spacecraft against debris up to 1 mm in size.
Q12: What measures are already being taken to avoid space debris - and which ones need to be taken in the future?
Spacecraft operators are currently focusing their efforts on controlling the space debris environment. The ultimate goal is to prevent a collisional cascading process from setting in over the next few decades. Initial steps aim at reducing the generation of hazardous debris by avoiding in-orbit explosions or collisions with operational spacecraft, and by removing spacecraft from densely populated altitude regions at the end of their mission. These measures can stabilise the environment in the short term, but need to be applied by all spacefaring organisations immediately.
In the long term, at least some of the existing in-orbit mass, which fuels the collisional cascading process, must be removed. This can be most efficiently done by space debris remediation activities that actively remove old spacecraft and rocket stages, in which most of the mass is concentrated. These, however, are costly.
Regardless of cost, long-term debris environment projections indicate that removal of existing in-orbit mass is a mandatory step to maintain the space debris environment at a safe level for future space operations.
Q13: Which international agreements cover space debris mitigation?
There is an international consensus on the necessary space debris mitigation measures. The most prominent international body where such measures are discussed and elaborated is the Inter-Agency Space Debris Coordination Committee (IADC).
In addition to ESA, IADC membership comprises:
- Italy - ASI (Agenzia Spaziale Italiana)
- France - CNES (Centre National d'Etudes Spatiales)
- China - CNSA (China National Space Administration)
- Canada - CSA (Canadian Space Agency)
- Germany - DLR (German Aerospace Center)
- India - ISRO (Indian Space Research Organisation)
- Japan - JAXA (Japan Aerospace Exploration Agency)
- USA - NASA (National Aeronautics and Space Administration)
- Russia - ROSCOSMOS (Russian Federal Space Agency)
- Ukraine - SSAU (State Space Agency of Ukraine)
- United Kingdom – UK Space Agency
In 2002 (with updates in 2007), IADC produced a set of mitigation guidelines, which also served as input to a set of seven Space Debris Mitigation Guidelines adopted by the United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS). The required steps are:
- Limit debris release during normal operations
- Minimise the potential for break-ups during operational phases
- Limit the probability of accidental collisions
- Avoid intentional destruction and other harmful activities
- Minimise the potential for post-mission break-ups resulting from stored energy (e.g. remaining on-board fuel)
- Limit the long-term presence of spacecraft and launch vehicle orbital stages in the low-Earth orbit region after the end of their mission
- Limit the long-term interference of spacecraft and launch vehicle orbital stages with the geosynchronous region after their end of mission
For example, one strategy that is fully compliant with the IADC guidelines would be to preserve enough fuel on board a satellite to perform a deorbiting manoeuvre at the end of the mission and to passivate on-board systems. So long as the manoeuvre brought the satellite to a low enough orbit such that it would re-enter the atmosphere (due to air drag) within 25 years, the guidelines would be fully respected.
What could be the next steps?
The agreed-upon space debris mitigation measures must be followed by space debris environment remediation measures. Such measures are presently being discussed at the International Academy of Astronautics (IAA) and the UN Long-term Sustainability of Outer Space Activities Working Group.
Q14: What does ESA plan to remove space debris objects from orbit?
It is agreed today that the number of objects in LEO can only be controlled by active removal of selected objects (5 to 10 large objects, such as complete defunct satellites, per year). As this is a global task, active removal is a challenge that should be undertaken by joint efforts and ESA, as a space technology and operations agency, has identified active removal technologies as a strategic goal.
ESA’s planned CleanSpace Initiative is organised around four distinct branches, of which two are closely linked to space debris:
- Green technologies
- Space debris mitigation
- Technologies for space debris remediation.
CleanSpace will look at the required technology developments, development of advanced guidance, navigation, control sensors and capture-and-berth technologies combined with targeted de-orbit techniques for the compound spacecraft. Technologies for a wide range of removal targets will be studied, including real- applications.
Clean Space is being introduced as a cross-cutting theme within ESA's Technology programmes as part of Agenda 2015.
Q15: How many objects re-enter every year, and will this be dangerous?
Only a few large objects re-enter every year. In total, about 75% of the larger objects ever launched have already re-entered. Objects of moderate size re-enter about once per week, while small-sized tracked space debris objects re-enter almost daily.
In general, most objects burn up entirely in the atmosphere during the re-entry. Parts of larger objects, or components that are made of material with a high melting point, may impact the ground or ocean surface. As these are rare events, and as about 75% of the Earth’s surface is covered by water and large portions of land mass are uninhibited, the related risk for a single individual is several orders of magnitude smaller than commonly accepted risks, such as driving a car, taken in day-to-day life.
Prof Dr Heiner Klinkrad
Head of Space Debris Office
64293 Darmstadt, Germany
email: Heiner.Klinkrad [at] esa.int