Space debris

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Distribution of space debris. Each point marks an object in the catalog, typically> 5 cm. (not to scale)

Space debris , also called space junk , consists of artificial objects with no practical value, which are in orbits around the earth and represent a danger to space travel .

According to models such as MASTER-2005 (Meteoroid and Space Debris Terrestrial Environment Reference) from ESA , there are over 600,000 objects with a diameter greater than 1 cm in orbits around the earth. Around 13,000 objects from 5 cm are continuously observed using the US space surveillance system . The Joint Space Operations Center of the United States Strategic Command knew in 2009 of more than 18,500 man-made celestial bodies.

As part of measurement campaigns, sporadic measurements are carried out with radar systems and telescopes in order to at least statistically record smaller objects and to validate space debris models such as MASTER. This is achieved using bistatic radar with the Goldstone radio telescope up to 2 mm in diameter for objects in near-earth orbit (LEO). For the geostationary orbit (GEO) optical telescopes have the smaller limit size: the ESA Space Debris Telescope at the Teide Observatory on Tenerife reaches 10 cm .

Impact in the solar cell wing of the SMM satellite. The hole is 0.5 mm in diameter, the impactor significantly less.

Another source of information about the distribution of space debris is traced satellite surfaces. These include the solar cells of the Hubble space telescope . A large number of impact craters were recorded and evaluated on the latter. Spectroscopic analyzes made it possible to draw conclusions about the composition and thus possible sources of the impacted objects.

distribution

Height dependence of the number density of particles larger than 1 mm. 2001 data

The number of particles varies with height. Below 400 km they burn up within a few years. They accumulate in the orbits of 600 km to 1500 km ( sun-synchronous orbit ) and 36,000 km (geostationary orbit), which are preferred by satellites .

Number per m² and year depending on the particle size

The particle flux (number of particles that pass an area of ​​one square meter per year) varies with size. The measured distribution (red curve in the diagram) follows a power law with exponent 4 (blue straight line) over several orders of magnitude . These particles are meteoroids of natural origin. The deviation for particles smaller than 0.1 mm is caused by the solar wind. Space debris dominates above 10 mm.

Risks

The relative speed between space debris and a near-Earth satellite with a high inclination of the orbit is on the order of ten kilometers per second. Due to the high speed, a particle with a mass of 1 g has an energy of 50 kJ, which corresponds to the explosive force of about 12 g TNT , so that both the particle and the material immediately hit explode.

The manned modules of the International Space Station (ISS) are equipped with double-walled meteoroid shields ( Whipple shield ) and can withstand impacts of space debris with a diameter of several centimeters due to the scattering effect created by the impact in the first wall.

The probability of failure of operational satellites caused by impacts by space debris is already no longer negligible in some orbits. Even impacts of smaller particles in the sub-millimeter range can damage sensitive payloads or perforate spacesuits.

In 2007, the People's Republic of China deliberately shot down its Fengyun-1C weather satellite from the ground to demonstrate its anti-satellite missile capabilities. However, this resulted in a cloud of at least 40,000 debris in space. The largest accidental collision in space to date was the satellite collision on February 10, 2009 . A deactivated Russian communications satellite and an Iridium satellite collided at an altitude of 789 km over northern Siberia. Both satellites were destroyed. The collision released a significant amount of further space debris.

The collision rate of objects of the order of 10 cm with one of the many satellites is estimated at one event every 10 years.

The manned International Space Station, but also many of the satellites, are able to perform evasive maneuvers in order to avoid a collision (probability p = 1 / 10,000) with one of the approximately 13,000 objects whose orbits are continuously tracked, which is classified as not unlikely. The Envisat earth observation satellite carried out two such maneuvers back in 2004 . Space shuttles such as the Discovery had to fly a total of six evasive maneuvers. The ISS had successfully carried out eight evasive maneuvers by 2009.

amounts

By spring 2010, around 4700 rocket launches with a good 6100 satellites had taken place in 50 years of space travel. Of this, 15,000 fragments of rockets and satellites remained, up to complete upper stages. According to the USA catalog, that is 15,000 objects that are at least ten centimeters in size, and there are presumably 7,000 objects kept secret. If the minimum size is reduced to one centimeter, 600,000 objects are estimated, to which about a million smaller particles are added. This results in the total mass of space debris of about 6300 tons, of which 73% of the objects are in near-earth orbit (LEO), but this is only 40% of the total mass, i.e. about 2700 tons. The altitude of 800 kilometers, the preferred trajectory of the reconnaissance satellites, is particularly affected. The ISS flies between 350 and 400 kilometers; So far she has had to avoid objects larger than one centimeter several times. In geostationary orbit (GEO) at an altitude of 36,000 kilometers around the earth, only 8% of the fragments are located, but here the large telecommunications satellites, each weighing several tons, orbiting an estimated total weight of 33%, i.e. around 2000 tons. The remaining 19% of the objects with 27% of the mass are on other tracks.

“Even if you stopped space travel today, the current mass of debris in orbit would be sufficient [due to the cascade effect ...] to keep creating new debris. [...] In the long term, the increase in space debris can mean that certain orbits can otherwise no longer be used for space travel. "

- Heiner Klinkrad (Head of the Space Debris Office at ESA in Darmstadt.)

Sources and sinks

Creation of new space debris

In addition to satellites that are no longer in use, there are a number of events and mechanisms that lead to the creation of space debris.

Detached second stage of a Delta II rocket in orbit, imaged by the XSS 10 experimental satellite
Mission-related objects

Objects released in the course of mission-related objects (MRO), such as explosive bolts and covers. Also whole rocket upper stages and double launch devices that enter orbit with the satellites and remain there.

Explosions

from satellites or upper stages - these are caused by deliberate detonations, by the ignition of residual fuels from upper stages and by the evaporation of cryogenic fuel components in upper stages in which fuel residues are still left. The expansion of these fuels as they evaporate can blow up the upper stages. Explosions can also be triggered by discharges in the satellites' batteries. It is believed that around 200 explosions have occurred in orbit since space travel began.

Killer satellites

Satellites that were used during the Cold War - and probably still today - specifically to neutralize the enemy's spy satellites . Most self-destructively cause an intentional collision with the target, sometimes accompanied by an explosion. Neither their numbers nor that of their victims are publicly known, as both themselves and their targets are under the strictest military secrecy.

the lanes of cataloged Fengyun-1C fragments one month after the ASAT test
Height distribution of fragments in the LEO according to Fengyun-1C and the collision in 2009
Anti-satellite missiles (ASAT)

The use of these weapons can hurl the debris created by the destruction of satellites (such as Fengyun-1C ) in many different orbits - including those that reach great heights.

Spacecraft collisions

It is not about scratches caused by unsuccessful docking maneuvers, but about random encounters with high relative speed, in the GEO usually with 100 to 1000 m / s, but possibly also with 1.5 km / s (satellite against Hohmann transfer stage), in the LEO with typically 10 km / s, which dismantles both missiles. Examples are the separation of the stabilization mast of the Cerise satellite (retractable mast) by an older Ariane rocket upper stage and the spectacular satellite collision on February 10, 2009 , during which over 2000 cataloged debris and roughly half a million particles over 1 mm arose.

Continued collisions

In 1978, NASA consultant Donald J. Kessler predicted the scenario known as Kessler Syndrome , according to which many larger fragments would be formed when small fragments and meteoroids hit , and the garbage problem would grow at an accelerated rate, even if no more satellites were launched.

Surface degradation

The ESA Space Debris Telescope often found bright objects whose rapid sinking in the high atmosphere indicates a very high area-to-mass ratio, up to 30 m² / kg. It could be heat protection film from satellites.

West Ford Dipoles

At the beginning of the 1960s, a diffuse sphere made up of many millions of fine wires (18 mm × 0.018 mm) was supposed to form a reflector for radio communications. Isolation during the release was only partially successful; flakes formed, of which a manageable number still wandered about at an altitude of over 2500 km.

A piece of aluminum from a test of a space shuttle - Boosters
Solid propulsion

generate micrometer-sized aluminum oxide particles during combustion. At the end of the burn-up, larger slag objects can also emerge, the diameter of which can reach several centimeters.

Reactor coolant

from space-based Buk nuclear reactors from Soviet spy satellites of the series known in the West as RORSAT . In 16 such satellites, the reactor core was repelled after the mission was completed, releasing the coolant of the primary cooling circuit NaK -78 (approx. 8 kg each). The NaK was distributed in droplets of various sizes on the orbits of the RORSAT satellites. However, due to various path disturbances and the rotation of the junction line, the NaK is also increasingly being distributed to other paths.

Burning up of space debris from low orbits

Lifespan at different heights

The parts in low orbits are slowed down by a residual amount of air resistance and eventually burn up in the atmosphere . At higher altitudes, the air friction decreases, so that larger objects need decades from an altitude of 800 km, but a few thousand years to burn up from an altitude of 1500 km. The fine wires of the West Ford project , however, as far as they were not clumped, returned within a few years from an altitude of over 3,500 km, as calculated with the support of the radiation pressure of the sun.

  • Lifetime diagrams of spacecraft in highly elliptical orbits at different altitudes.

  • Lifetime diagrams of spacecraft in weakly elliptical orbits at different altitudes.

As the heights of 800 km and 1500 km are preferred as orbits, the threat to commercial and scientific space travel is growing. Concepts of how to solve this problem are currently failing due to the associated costs.

Examples of partial burn-up

With very large satellites and especially with heat-resistant components, it can happen that these partially survive the re-entry and that some very heavy fragments reach the earth. Examples include ROSAT with heat-resistant mirrors made of glass ceramic or the 5.9-ton Upper Atmosphere Research Satellite .

activities

Preventive measures

In order to avoid collisions with parts of the space debris, all larger particles (from 1 cm in size) are permanently tracked by the responsible NASA and military observatories. If a collision course with the ISS or another maneuverable spacecraft is detected, this typically occurs early enough (several days in advance) that this spacecraft can initiate an evasive maneuver. Since the ISS has to be brought back to a slightly higher orbit anyway, this does not cost any additional fuel.

To avoid space debris in all modern rockets, the stages that enter orbit are slowed down again with the help of an additional engine ignition so that they burn up in the atmosphere sooner or later. The ESA suggests limiting the time until re-entry of mission-related objects (MROs, see above ) depending on the cross-sectional area:

  • A - cross-sectional area
  • t - duration of use

In upper stages, which enter high orbits and cannot generate sufficient braking impulse, at least the remains of the fuel are used up or drained to prevent a possible explosion. Geostationary satellites themselves are no longer used until the fuel supplies are completely exhausted, but are brought into cemetery orbit with a certain amount of remainder .

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 remove at least larger inactive objects. Various ideas have been suggested how to dispose of multiple objects in a single, longer mission. Problematic aspects are the interaction with uncontrolled rotating objects and the great need for supporting mass for numerous path changes.

Measures to clear space debris

In December 2019, the ESA Council of Ministers decided to test and carry out the ClearSpace-1 mission to remove space debris from the earth's atmosphere from 2025.

Measurements

Space debris can be detected from the ground using optical telescopes or radar. Some radars can detect particles in the millimeter range in low orbits. The exact measurement of the path parameters and the continuous tracking of the objects is only possible with diameters from 5 cm in LEO and 50 cm in GEO. The paths of these objects are continuously tracked by the American Space Surveillance System and their path elements are published in an object catalog. This catalog currently contains around 13,000 objects, but only the path data for around 9,600 objects are accessible to the public. In-situ measurements are the only way to determine the population and orbit parameters of smaller particles. Several detector concepts have already been tested for this purpose. The best-known European detector concepts are the DEBIE detector and the GORID detector (identical to Galileo and Ulysses detectors). Both detectors determine the impact energy of a high-speed particle via the composition of the plasma produced by the impact. The electrons and ions in the plasma are separated from each other with electrical fields and the respective voltage is measured with charged grids. From the shape and the temporal progression of the voltage pulses, the mass and speed of the impacted particle can be determined using calibration curves recorded on the ground. In addition to pure plasma measurement, the DEBIE sensor also measures the impact pulse via piezo elements, so that there is a comparison signal for the plasma measurement. A plan to capture and analyze space debris with the Large Area Debris Collector (LAD-C) at the ISS was abandoned in 2007.

Long Duration Exposure Facility (LDEF)

The LDEF satellite was an experiment designed to study the long-term effects of a space environment. Although it was planned to be much shorter, the satellite stayed in orbit for almost six years before it was recovered by mission STS-32 and brought back to Earth. Apart from a lot of damage that was only visible microscopically, there was also one that was visible to the naked eye. The investigation of the satellite brought a lot of information about space debris and micrometeorites .

Catalogs

The catalogs about artificial satellites, for example NORAD , are limited to intact objects. The debris that arises from a breakup is recorded in separate databases for space debris. One, like NORAD, is maintained by USSTRATCOM . It is also the basis for the DISCOS collection ( Database and Information System Characterizing Objects in Space ) of the ESA .

See also

literature

  • Carsten Wiedemann, Peter Vörsmann, Heiner Klinkrad: A model for space debris . In: Stars and Space . October 2005, pp. 30-36.
  • Paula H. Krisko: The Predicted Growth of the Low Earth Orbit Space Debris Environment: An Assessment of Future Risk for Spacecraft. Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, Vol. 221, 2007, doi: 10.1243 / 09544100JAERO192 ( online ).
  • Wolfgang Rathgeber, Kai-Uwe Schrogl, Ray A. Williamson (Eds.): The Fair and Responsible Use of Space: An International Perspective . Springer, Vienna 2010, ISBN 978-3-211-99652-2 , limited preview in the Google book search.
  • Michael W. Taylor: Orbital Debris - Technical and Legal Issues and Solutions. McGill University, Montreal 2006, abstract online (pdf, p. 121, accessed November 2, 2009; 669 kB)
  • P. Eichler, A. Bade: Removal of debris from orbit. American Institute of Aeronautics and Astronautics 1990-1366, aiaa.org
  • Orbital Debris Program Office (NASA): History of ON-Orbit Satellite Fragmentation 14th Edition June 2008 History of ON-Orbit Satellite Fragmentation (pdf)
  • Daniel Hampf, Leif Humbert, Thomas Dekorsy and Wolfgang Riede: Cosmic Garbage Dump . Physik Journal (DPG) 01/2018, p. 31.

Web links

Commons : Space junk  - album with pictures, videos and audio files
Wiktionary: Space debris  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ D. Spencer et al .: Space Debris Research in the US Department of Defense. Second European Conference on Space Debris, 1997, ESOC, Darmstadt, Germany (1997), ESA-SP 393., p. 9, @ adsabs.harvard.edu
  2. ↑ Gerhard Hegmann: Near-Accident: Disused satellites in a cloud of debris on a collision course . In: THE WORLD . January 8, 2017 ( welt.de [accessed March 9, 2020]).
  3. ↑ spaceweather.com
  4. ↑ ESA: Space debris: How high is the risk? March 22, 2005.
  5. ↑ Joseph N. Pelton: Space debris and other threats from outer space. Springer, New York 2013, ISBN 978-1-4614-6713-7 .
  6. ^ Orbital Debris and Future Environment Remediation nasa.gov, accessed March 7, 2015.
  7. ↑ Space station has to avoid space junk. spiegel.de, January 28, 2012, accessed on January 29, 2012 .
  8. ↑ Space station flees from satellite debris. spiegel.de, January 13, 2012, accessed on January 29, 2012 .
  9. ↑ Space station circumnavigates space junk. spiegel.de, October 27, 2011, accessed on January 29, 2012 .
  10. ↑ ESA specifications for vdi-n of 2 July 2010, p. 3
  11. ↑ US Space Debris envinronment, Operations, and Policy updates. (PDF) In: NASA. UNOOSA, accessed October 1, 2011 .
  12. ↑ Uwe Reichert: Environmental disaster in orbit. In: Stars and Space . 46, No. 4, April 2007, p. 24, ISSN  0039-1263
  13. ↑ http://www.esa.int/ger/ESA_in_your_country/Germany/Weltraummuell_Wie_hoch_ist_das_Risiko_einzuschaetzen/(print)
  14. ↑ Donald J. Kessler, Burton G. Cour-Palais: Collision Frequency of Artificial Satellites - The Creation of a Debris Belt. (3.4 MB PDF) In: Journal of Geophysical Research Vol 81. No. 46 June 1, 1978, pp. 2637-2646 , archived from the original on May 15, 2011 ; accessed on May 3, 2010 (English).
  15. ^ A b West Ford Needles: Where are They Now? In: NASA : Orbital Debris Quarterly News. Vol. 17, Issue 4, October 2013, p. 3.
  16. ↑ C. Wiedemann, H. Krag, P. Wegener, P. Vörsmann: Yearbook 2002 of the DGLR, Volume II, pp. 1009-1017. The orbital behavior of clusters of copper needles from the West Ford experiments ( Memento of January 8, 2010 in the Internet Archive ).
  17. ↑ S. Stabroth, P. Wegener, M. Oswald, C. Wiedemann, H. Klinkrad, P. Vörsmann: Introduction of a nozzle throat diameter dependency into the SRM dust size distribution. In: Advances in Space Research. 38, 2006, pp. 2117-2121.
  18. ↑ J.-C. Liou, Nicholas L. Johnson: A sensitivity study of the effectiveness of active debris removal in LEO. Acta Astronautica, 2009, doi: 10.1016 / j.actaastro.2008.07.009 ( online ).
  19. ↑ ESA commissions world's first space debris removal. Retrieved December 9, 2019 .
  20. ^ Maggie McKee: World's only space dust detector binned. February 12, 2007, accessed October 9, 2013 .
  21. ↑ Page of NASA about LDEF (English with pictures)
  22. ^ Situation of Space debris in 1995
  23. ↑ DISCOS of ESA