By

Cheparthy Akash- A20405219055. Putta Yuvaraj Gupta- A20405219053. Dadi Venu -A20405219131. Uppu Balaji -A20405219035. D Madhuvardhan- A20405219118. B .Tech cse. Semester 3. Section B.

Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) is a term for defunct human-made objects in space principally in Earth orbit which no longer serve a useful function. These include derelict spacecraft nonfunctional spacecraft and abandoned launch vehicle stages mission-related debris, and particularly numerous in Earth orbit, fragmentation debris from the breakup of derelict rocket bodies and spacecraft. In addition to derelict human-built 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 rocket motors. Space debris represents a risk to spacecraft.

A computer-generated image representing space debris as could be seen from high earth orbit. The two main debris fields are the ring of objects in geosynchronous earth oirbit(GEO) and the cloud of objects in low earth orbit (LEO).

Space debris is typically a negativie it creates an external cost on others from the initial action to launch or use a spacecraft in near-Earth orbit a cost that is typically not taken into account nor fully accounted for in the cost by the launcher or payload owner.Several spacecraft, both manned and unmanned, have been damaged or destroyed by space debris. The measurement, mitigation, and potential removal of debris are conducted by some participants in the space industry.

As of October 2019, the US surveillance netork reported nearly 20,000 artificial objects in orbit above the Earth, including 2,218 operational satellites. However, these are just the objects 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 of pieces larger than 10 cm were estimated to be in orbit around the Earth. When the smallest objects of human-made space debris (paint flecks, solid rocket exhaust particles, etc.) are grouped with micro meteoroids, 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 sand blasting, especially to solar panels and optics like telescopes or star trackers that cannot easily be protected by a ballistic  shield.

By Cheparthy Akash.

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 aolar maximum  (due to the heating and expansion of the Earth’s atmosphere), but one about every three days at ailar 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 political, legal, economic and cultural “rules of the game”—are the greatest impediment to the cleanup of near-Earth space. There is no commercial incentive, since costs aren’t assigned to polluters, but a number of suggestions have been made. 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 removal of space debris has been evalauted by the space Generation adviory Council including French astrophysicist.

Growth mitigation

Spatial density of LEO space debris by altitude, according to 2011 a NASA report to the united nation office for outet space Affairs.

Spatial density of space debris by altitude according to ESA MASTER-2001, without debris from the Chinese ASAT and 2009 collision events

As of the 2010s, several technical approaches to the mitigation of the growth of space debris are typically undertaken, yet no comprehensive legal regime or cost assignment structure is in place to reduce space debris in the way that terrestrial pollution has reduced since the mid-20th century.

To avoid excessive creation of artificial space debris, many—but not all—satellites launched to above-low-Earth-orbit are launched initially into elliptical orbits  with perigees inside Earth’s atmosphere so the orbit will quickly decay and the satellites then will destroy themselves upon reentry into the atmosphere. Other methods are used for spacecraft in higher orbits. These include passivation  of the spacecraft at the end of its useful life; as well as use of upper stages that can reignite to decelerate the stage to intentionally deorbit it, often on the first or second orbit following payload release; satellites that can, if they remain healthy for years, deorbit themselves from the lower orbits around Earth. Other satellites (such as many CubeSats) in low orbits below approximately 400 km orbital altitude depend on the energy-absorbing effects of the upper atmosphere to reliably deorbit a spacecraft within weeks or months.

Increasingly, spent  upper stages in higher orbits—orbits for which low-delta-v deorbit is not possible, or not planned for—and architectures that support satellite passivation, at end of life are passivated at end of life. This removes any internal energy contained in the vehicle at the end of its mission or useful life. While this does not remove the debris of the now derelict rocket stage or satellite itself, it does substantially reduce the likelihood of the spacecraft destructing and creating many smaller pieces of space debris, a phenomenon that was common in many of the early generations of US and Soviet spacecraft.

Upper stage passivation (e.g. of Delta boosters) by releasing residual propellants reduces debris from orbital explosions; however even as late as 2011, not all upper stages implement this practice. SpaceX used the term “propulsive passivation” for the final maneuver of their six-hour demonstration mission of the Falcon 9 second stage for the US Air Force in 2019, but did not define what all that term encompassed.

By Putta Yuvaraj Gupta.

Self-removal

Although the ITU requires geostationary satellites to move to a graveyard orbit at the end of their lives, the selected orbital areas do not sufficiently protect GEO lanes from debris.Rocket stages (or satellites) with enough propellant may make a direct, controlled de-orbit, or if this would require too much propellant, a satellite may be brought to an orbit where atmospheric drag would cause it to eventually de-orbit. This was done with the French spot1 satellite ,reducing its atmospheric re-entry time from a projected 200 years to about 15 by lowering its altitude from 830 km (516 mi) to about 550 km (342 mi).

The Iridium constellations 95 communication satellites launched during the five-year period between 1997 and 2002 provides a set of data points on the limits of self-removal. The satellite operator Iridium communications remained operational (albeit with a company name change through a corporate bankruptcy during the period) over the two-decade life of the satellites, and by December 2019, had “completed disposal of the last of its 65 working legacy satellites.”However, this process left nearly one-third of the mass of this constellation (30 satellites, 20,400 kg (45,000 lb) of materiel) in LEO orbits at approximately 700 km (430 mi) altitude, where self-decay is quite slow. 29 of these satellites simply failed during their time in orbit and were thus unable to self-deorbit, while one i iradium 33was involved in the 2009 satellite collision  with the  Russian military satellite.No “Plan B” provision was designed in for removal of the satellites that were unable to remove themselves. However, in 2019, Iridium CEO  said that Iridium would be willing to pay an active-debris-removal company to deorbit its remaining first-generation satellites if it were possible for a sufficiently low cost, say “US$10,000 per deorbit, but [he] acknowledged that price would likely be far below what a debris-removal company could realistically offer. ‘You know at what point [it’s] a no-brainer, but [I] expect the cost is really in the millions or tens of millions, at which price I know it doesn’t make sense'”

Passive methods of increasing the orbital decay rate of spacecraft debris have been proposed. Instead of rockets, an electrodynamic tethere could be attached to a spacecraft at launch; at the end of its lifetime, the tether would be rolled out to slow the spacecraft. Other proposals include a booster stage with a sail-like attachment and a large, thin, inflatable balloon envelope.

External removal

A variety of approaches have been proposed, studied, or had ground subsystems built to use other spacecraft to remove existing space debris. A consensus of speakers at a meeting in Brussels in October 2012, organized by the Secure World Foundation (a U.S. think tank) and the French International Relations Institute, reported that removal of the largest debris would be required to prevent the risk to spacecraft becoming unacceptable in the foreseeable future (without any addition to the inventory of dead spacecraft in LEO). To date in 2019, removal costs and legal questions about ownership and the authority to remove defunct satellites have stymied national or international action. Current space law retains ownership of all satellites with their original operators, even debris or spacecraft which are defunct or threaten active missions.

Moreover, as of 2006, the cost of any of the proposed approaches for external removal is about the same as launching a spacecraft and, according to NASA’s Nicholas Johnson,not cost-effective.

This is beginning to change in the late 2010s, as some companies have made plans to begin to do external removal on their satellites in mid-LEO orbits. For example, one web will utilize on-board self-removal as “plan A” for satellite deorbiting at the end of life, but if a satellite is unable to remove itself within one year of end of life, OneWeb will implement “plan B” and dispatch a reusable (multi-transport mission) space tug to attach to the satellite at an already built-in capture target via a grappling fixture, to be towed to a lower orbit and released for reentry.

By Uppu Balaji.

Remotely controlled vehicles

A well-studied solution uses a remotely controlled vehicle  to rendezvous with, capture and return debris to a central station.One such system is space Infrastructure servicing a commercially develoed refueling depot and service spacecraft for communications satellites in geosynchronous orbit originally scheduled for a 2015 launch.The SIS would be able to “push dead satellites into graveyard orbits.” The Advanced common Evolved stage family of upper stages is being designed with a high leftover-propellant margin (for derelict capture and de-orbit) and in space refueling  capability for the high delta v  required to de-orbit heavy objects from geosynchronous orbit. A tug-like satellite to drag debris to a safe altitude for it to burn up in the atmosphere has been researched. When debris is identified the satellite creates a difference in potential between the debris and itself, then using its thrusters to move itself and the debris to a safer orbit.

A variation of this approach is for the remotely controlled vehicle to rendezvous with debris, capture  it temporarily to attach a smaller se orbit satellite  and drag the debris with a tether to the desired location. The “mothership” would then tow the debris-smallsat combination for atmospheric  or move it to a graveyard orbit. One such system is the proposed , which would carry over 40 SUL (satellite on umbilical line) de-orbit satellites and propellant sufficient for their removal.

Cleanspace One

On 7 January 2010 Star, Inc. reported that it received a contract from the space and Navel warfaresystem command for a feasibility study of the ElectroDynamic Debris Eliminator (EDDE) propelalents spacecraft for space-debris removal. In February 2012 the Swiss Space Center Lausanne  announced the Clean Space One project, a nano satellite  demonstration project for matching orbit with a defunct Swiss nanosatellite, capturing it and de-orbiting together. The mission has seen several evolutions to reach a pac-man inspired capture model. In 2013, Space Sweeper with Sling-Sat (4S), a grappling satellite which captures and ejects debris was studied.

In December 2019, the European space Agency  awarded the first contract to clean up space debris. The €120 million mission dubbed  (a spinoff from the EPFL project) is slated to launch in 2025. It aims to remove a 100 kg VEga Secondary Payload Adapter (Vespa) left by vega flight VV02 in an 800 km orbit in 2013. A “chaser” will grab the junk with four robotic arms and drag it down to Earth’s atmosphere where both will burn up.

By Dadi Venu

Laser methods

The laser broom uses a ground-based laser  to ablate the front of the debris, producing a rocket-like thrust which slows the object. With continued application, the debris would fall enough to be influenced by atmospheric drag. During the late 1990s, the U.S. Air Force’s Project Orion was a laser-broom design.Although a test-bed device was scheduled to launch on a Space Shuttle in 2003, international agreements banning powerful laser testing in orbit limited its use to measurements.The space shutle columbia  disaster postponed the project and according to Nicholas Johnson, chief scientist and program manager for NASA’s Orbital Debris Program Office, “There are lots of little gotchas in the Orion final report. There’s a reason why it’s been sitting on the shelf for more than a decade.”

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. A similar proposal places the laser on a satellite in  using a pulsed beam to push satellites into lower orbits to accelerate their reentry. A proposal to replace the laser with an ion beamed has been made,and other proposals use a foamy ball of aerogel or a spray of water, inflatable balloons,electrodynamic tethers , and dedicated anti-satellite weapons.

Nets

On 28 February 2014, Japan’s Japan Areospace Exploration Agency (JAXA) launched a test “space net” satellite. The launch was an operational test only. In December 2016 the country sent a space junk collector via kountori 6to the ISS by which JAXA scientists experiment to pull junk out of orbit using a tether. The system failed to extend a 700-meter tether from a space station resupply vehicle that was returning to Earth. On 6 February the mission was declared a failure and leading researcher Koichi Inoue told reporters that they “believe the tether did not get released”.

Since 2012, the European Space Agency has been working on the design of a mission to remove large space debris from orbit. The mission, is scheduled for launch during 2023 with an objective to remove debris heavier than 4,000 kilograms (8,800 lb) from LEO. Several capture techniques are being studied, including a net, a harpoon and a combination robot arm and clamping mechanism.

Harpoon

The Remove debris mission plan is to test the efficacy of several ADR technologies on mock targets in low earth orbit . In order to complete its planned experiments the platform is equipped with a net, a harpoon, a laser ranging instrument, a dragsail, and two  (miniature research satellites). The mission was launched on 2 April 2018.

By D Madhuvardhan.

Thank you.