Experimental Space debris - Polluted Space with no return

Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) is defunct artificial objects in space—principally in Earth orbit—that no longer serve a useful function. These include derelict spacecraft—nonfunctional spacecraft and abandoned launch vehicle stages—mission-related debris, particularly numerous in Earth orbit, fragmentation debris from the breakup of derelict rocket bodies and spacecraft. In addition to derelict man-made objects left in orbit, other examples of space debris include fragments from their disintegration, erosion, and collisions or even paint flecks, solidified liquids expelled from spacecraft, and unburned particles from solid rockets motors. Space debris represents a risk to spacecraft.

As of January 2021, the US Space Surveillance Network reported 21,901 artificial objects in orbit above the Earth including 4,450 operational satellites. However, these are just objects that are large enough to be tracked. As of January 2019, more than 128 million pieces of debris smaller than 1 cm (0.4 in), about 900,000 pieces of debris 1–10 cm, and around 34,000 pieces larger than 10 cm (3.9 in) were estimated to be in orbit around the Earth. When the smallest objects of artificial space debris (paint flecks, solid rocket exhaust particles, etc.) are grouped with micrometeoroids, they are together sometimes referred to by space agencies as MMOD (Micrometeoroid and Orbital Debris). Collisions with debris have become a hazard to spacecraft; the smallest objects cause damage akin to sandblasting, especially to solar panels and optics like telescopes or star trackers that cannot easily be protected by a ballistic shield.

Debris keep growth

Space debris began to accumulate in Earth orbit immediately with the first launch of an artificial satellite Sputnik 1 into orbit in October 1957. But even before that, besides natural ejecta from Earth, humans might have produced ejecta that became space debris, as in the August 1957 Pascal B test. After the launch of Sputnik, the North American Aerospace Defense Command (NORAD) began compiling a database (the Space Object Catalog) of all known rocket launches and objects reaching orbit: satellites, protective shields, and upper-stages of launch vehicles. NASA later published modified versions of the database in a two-line element set, and beginning in the early 1980s the CelesTrak bulletin board system re-published them.

During the 1980s, NASA and other U.S. groups attempted to limit the growth of debris. One trial solution

was implemented by McDonnell Douglas for the Delta launch vehicle by having the booster move away from its payload and vent any propellant remaining in its tanks. This eliminated one source for pressure buildup in the tanks which had previously caused them to explode and create additional orbital debris.

A new battery of studies followed as NASA, NORAD and others attempted to better understand the orbital environment, with each adjusting the number of pieces of debris in the critical-mass zone upward. Although in 1981 (when Schefter's article was published) the number of objects was estimated at 5,000 new detectors in the Ground-based Electro-Optical Deep Space Surveillance system found new objects. By the late 1990s, it was thought that most of the 28,000 launched objects had already decayed and about 8,500 remained in orbit. By 2005 this was adjusted upward to 13,000 objects and a 2006 study increased the number to 19,000 as a result of an ASAT test and a satellite collision. In 2011, NASA said that 22,000 objects were being tracked.

In the 2009 European Air and Space Conference, University of Southampton researcher Hugh Lewis predicted that the threat from space debris would rise 50 percent in the next decade and quadruple in the next 50 years. As of 2009, more than 13,000 close calls were tracked weekly.

A 2011 report by the U.S. National Research Council warned NASA that the amount of orbiting space debris was at a critical level. According to some computer models, the amount of space debris "has reached a tipping point, with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures". The report called for international regulations limiting debris and research of disposal methods.

There are estimated to be over 128 million pieces of debris smaller than 1 cm (0.39 in) as of January 2019. There are approximately 900,000 pieces from 1 to 10 cm. The current count of large debris (defined as 10 cm across or larger) is 34,000. The technical measurement cutoff is c. 3 mm (0.12 in). As of 2020, there are 8000 metric tons of debris in orbit with no signs of slowing down.

A new Kessler effect

During the 1980s, the US Air Force (USAF) conducted an experimental program to determine what would happen if debris collided with satellites or other debris. The study demonstrated that the process differed from micrometeoroid collisions, with large chunks of debris created which would become collision threats.

In 1991, Kessler published "Collisional cascading: The limits of population growth in low Earth orbit with the best data then available. Citing the USAF conclusions about the creation of debris, he wrote that although almost all debris objects (such as paint flecks) were lightweight, most of its mass was in debris about 1 kg (2 lb 3 oz) or heavier. This mass could destroy a spacecraft on impact, creating more debris in the critical-mass area. According to the National Academy of Sciences:

A 1 kg object impacting at 10 km/s, for example, is probably capable of catastrophically breaking up a 1,000 kg spacecraft if it strikes a high-density element in the spacecraft. In such a breakup, numerous fragments larger than 1 kg would be created.

Kessler's analysis divided the problem into three parts. With a low-enough density, the addition of debris by impacts is slower than their decay rate and the problem is not significant. Beyond that is a critical density, where additional debris leads to additional collisions. At densities beyond this critical mass production exceeds decay, leading to a cascading chain reaction reducing the orbiting population to small objects (several centimeters in size) and increasing the hazard of space activity.

Debris generation and destruction

Every satellite, space probe, and crewed mission has the potential to produce space debris. The theoretical

cascading Kessler syndrome becomes more likely as satellites in orbit increase in number. As of 2014, there were about 2,000 commercial and government satellites orbiting the earth, and as of 2021 more than 4,000. It is estimated that there are 600,000 pieces of space junk ranging from 1 to 10 cm (¹⁄₂ to 4 in), and 23,000 are larger than that. On average one satellite is destroyed by collision with space junk each year. As of 2009, there had been four collisions between cataloged objects, including a collision between two satellites in 2009.

Orbital decay is much slower at altitudes where atmospheric drag is insignificant. Slight atmospheric drag, lunar perturbation, and solar wind drag can gradually bring debris down to lower altitudes where fragments finally re-enter, but this process can take millennia at very high altitudes.

A zombie satellite is a satellite that begins communicating again after an extended period of inactivity. It is a type of space debris, which describes all defunct human-made objects in outer space. At the end of their service life, the majority of satellites suffer from orbital decay and are destroyed by the heat of atmospheric entry. Zombie satellites, however, maintain a stable orbit but are either partially or completely inoperable, preventing operators from communicating with them consistently.

One technology proposed to help deal with fragments from 1 to 10 cm (¹⁄₂ to 4 in) in size is the laser broom, a proposed multimegawatt land-based laser that could deorbit debris: the side of the debris hit by

the laser would ablate and create a thrust that would change the eccentricity of the remains of the fragment until it would re-enter and be destroyed harmlessly. The momentum of the laser-beam photons could directly impart a thrust on the debris sufficient to move small debris into new orbits out of the way of working satellites. NASA research in 2011 indicates that firing a laser beam at a piece of space junk could impart an impulse of 1 mm (0.039 in) per second, and keeping the laser on the debris for a few hours per day could alter its course by 200 m (660 ft) per day. One drawback is the potential for material degradation; the energy may break up the debris, adding to the problem.

SpaceX's Starlink program raises concern among many experts about significantly worsening the possibility of Kessler Syndrome due to a large number of satellites the program aims to place in LEO, as the program's goal will more than double the satellites currently in LEO. In response to these concerns, SpaceX said that a large part of Starlink satellites are launched at a lower altitude of 550 km to achieve lower latency (versus 1,150 kilometers as originally planned), and failed satellites or debris are thus expected to deorbit within five years even without propulsion, due to atmospheric drag.

Dealing with debris

An average of about one tracked object per day has been dropping out of orbit for the past 50 years, averaging almost three objects per day at solar maximum (due to the heating and expansion of the Earth's atmosphere), but one about every three days at solar minimum, usually five and a half years later. In addition to natural atmospheric effects, corporations, academics, and government agencies have proposed plans and technology to deal with space debris, but as of November 2014, most of these are theoretical, and there is no extant business plan for debris reduction.

A number of scholars have also observed that institutional factors—political, legal, economic, and cultural "rules of the game"—are the greatest impediment to the cleanup of near-Earth space. There is little commercial incentive to act since costs are not assigned to polluters, though a number of technological solutions have been suggested. However, effects to date are limited. In the US, governmental bodies have been accused of backsliding on previous commitments to limit debris growth, "let alone tackling the more complex issues of removing orbital debris." The different methods for the removal of space debris have been evaluated by the Space Generation Advisory Council, including French astrophysicist Fatoumata Kébé.

There is no international treaty minimizing space debris. However, the United Nations Committee on the

Peaceful Uses of Outer Space (COPUOS) published voluntary guidelines in 2007, using a variety of earlier national regulatory attempts at developing standards for debris mitigation. As of 2008, the committee was discussing international "rules of the road" to prevent collisions between satellites By 2013, a number of national legal regimes existed typically instantiated in the launch licenses that are required for a launch in all spacefaring nations.

The voluntary ISO standard also adopted the "25-year rule" for the "LEO protected region" below 2,000 km (1,200 mi) altitude that has been previously (and still is, as of 2019) used by the US, ESA, and UN mitigation standards, and identifies it as "an upper limit for the amount of time that a space system shall remain in orbit after its mission is completed. Ideally, the time to deorbit should be as short as possible (i.e., much shorter than 25 years)".

Holger Krag of the European Space Agency states that as of 2017 there is no binding international regulatory framework with no progress occurring at the respective UN body in Vienna.