The proliferation of space debris in the Earth’s orbit

Christophe Bon­nal. There is now an addi­tion­al 12,000 objects. Today, there are 36,000 objects larg­er than 10 cm, 30,000 of which are well doc­u­ment­ed. These are so-called “cat­a­logued” objects, iden­ti­fied by a name or num­ber, whose tra­jec­to­ry is known. The remain­ing 6,000 are unref­er­enced mil­i­tary objects, or objects that are dif­fi­cult to track continuously.

Be warned, these “space objects” may be pieces of dead satel­lites or what are known as “oper­a­tional debris” such as straps, cov­ers, etc. As an oper­a­tor is not required to declare whether or not their satel­lite is live, it is dif­fi­cult to dis­tin­guish func­tion­al objects from space debris, but we do have some esti­mates. For exam­ple, we know there are 10,500 active satel­lites in orbit.

It’s hard to say. The def­i­n­i­tion of debris is “a non-func­tion­al space object of human ori­gin (…).” But what is “non-func­tion­al”? When Peter Beck, from the Cal­i­forn­ian start-up Rock­et Lab, sent a giant mir­ror ball one metre in diam­e­ter into space, the sci­en­tif­ic com­mu­ni­ty denounced the use­less­ness of the project. His response? The dis­co ball was an adver­tis­ing fea­ture, so could not be cat­e­gorised as debris… Beyond this anec­dote, the debate rages on, par­tic­u­lar­ly with the coun­tries that pol­lute the most. Today, 96% of orbital debris is the respon­si­bil­i­ty of the Unit­ed States, Rus­sia and Chi­na, with each coun­try account­ing for a third.

In 2023, there were 2,800 entries into orbit and 2,000 exits. These de-orbit­ing oper­a­tions are car­ried out in two ways: active with­draw­al, par­tic­u­lar­ly when there are humans in a cap­sule; and nat­ur­al de-orbit­ing linked to the dynam­ic pres­sure of the atmos­phere. The high­er the object, the slow­er it descends: ten years for a satel­lite at an alti­tude of 400 km, two cen­turies for those at 800 km and a thou­sand years for objects at 1,000 km.

Fur­ther­more, the mass of objects in orbit is 13,486 tonnes, which is a lit­tle more than the weight of the Eif­fel Tow­er, which is 10,000 tonnes. The con­ven­tion­al esti­mate is around 4,000 tonnes of use­less rock­et stages and approx­i­mate­ly 8,000 tonnes of satel­lites, half of which are thought to be non-func­tion­al. The most con­gest­ed area is in low orbit between 750 and 1,000 km. These are known as LEO (low Earth orbit) objects. In this area, the gen­er­a­tion of debris by col­li­sion is greater than the nat­ur­al destruc­tion by atmos­pher­ic re-entry. This caus­es a chain reac­tion known as the Kessler syndrome.

Not real­ly, but the 800 km orbit was the pre­ferred option for obser­va­tion satel­lites. At this alti­tude, there are a thou­sand times more pieces of debris than active satel­lites. This “rot­ten”, high­ly pol­lut­ed zone is not pro­hib­it­ed, and satel­lites can still be sent there, but their prob­a­bil­i­ty of pre­ma­ture destruc­tion by col­li­sion is now 10%. But the sit­u­a­tion is worsening.

In its lat­est report from Jan­u­ary 2025¹, the IADC (Inter-Agency Space Debris Coor­di­na­tion Com­mit­tee), the agency that brings togeth­er the world’s thir­teen major space agen­cies², con­cludes that “the amount of space debris could dou­ble in less than 50 years.” It has also pub­lished a unan­i­mous­ly approved note, which could be sum­marised as fol­lows: “Mit­i­ga­tion will not be enough. We need reme­di­a­tion.” In oth­er words, beyond the nat­ur­al decrease in space objects, we must imple­ment space reha­bil­i­ta­tion techniques.

It is a valid tech­nique that can be used to remove small debris, for exam­ple, but there are a mil­lion 1cm pieces of debris, so we’re not fin­ished yet! What’s more, these are large lasers that are con­sid­ered to be weapons.

To sta­bilise the envi­ron­ment, ten large pieces of debris would have to be removed each year before they frag­ment, while scrupu­lous­ly respect­ing cur­rent inter­na­tion­al reg­u­la­tions. The list of the 50 largest pieces of debris to be retrieved as a pri­or­i­ty was pub­lished in 2021³. The solu­tion would there­fore be a hunter with a robot­ic arm or a net to cap­ture the debris and bring it down to de-orbit it in the Pacif­ic. But there is a real obsta­cle: if we are tech­ni­cal­ly capa­ble of remov­ing our own debris, we would then be act­ing on for­eign space objects and there is a real notion of space war. Hence, the pro­found lack of enthu­si­asm of fund­ing bod­ies. Espe­cial­ly since the cur­rent esti­mates for a robot­ic garbage col­lec­tor in orbit are around 20 mil­lion euros, sev­er­al times the price of a new space object!

This is one of the sub­jects I am work­ing on, Design for non-Demise, or how to build space objects that do not melt at all on entry into the atmos­phere. Today, only 20% of the mass of a deor­bit­ed object ends up on the sur­face of the globe, main­ly because of mate­ri­als such as tita­ni­um, stain­less steel or car­bon. This leaves the prob­lem of the remain­ing 80% of the mass that has burned up in the atmos­phere, releas­ing aerosols such as alu­mi­na [Edi­tor’s note: alu­mini­um oxide] or soot, which direct­ly affect the ozone lay­er. In real­i­ty, the con­se­quences of these emis­sions are still unknown. With the arrival of satel­lite con­stel­la­tions such as Star­link and the pro­lif­er­a­tion of space oper­a­tions, this pol­lu­tion will unfor­tu­nate­ly increase exponentially.

Interview by Sophie Podevin

Find out more:

• Amer­i­can web­site for the gen­er­al pub­lic that allows users to fol­low cat­a­logued space objects in real time: https://​www​.space​-track​.org
• Arti­cle on the 50 biggest pieces of space debris in low orbit to be retrieved as a pri­or­i­ty: https://​cnes​.fr/​a​c​t​u​a​l​i​t​e​s​/​t​o​p​-​5​0​-​d​e​b​r​i​s​-​s​p​a​t​i​a​u​x​-​p​l​u​s​-​d​a​n​g​ereux (2021)
• First offi­cial IADC ref­er­ence guide on debris mit­i­ga­tion (2007): https://www.unoosa.org/documents/pdf/spacelaw/sd/IADC-2002–01-IADC-Space_Debris-Guidelines-Revision1.pdf
• Resource site of astro­physi­cist Jonathan McDow­ell, which archives data on all space objects: https://​plan​et4589​.org/​i​n​d​e​x​.html
• Sci­en­tif­ic study pub­lished in June 2024 on the pol­lu­tion caused by satel­lite de-orbit­ing on the ozone lay­er: https://​agupubs​.onlineli​brary​.wiley​.com/​d​o​i​/​1​0​.​1​0​2​9​/​2​0​2​4​G​L​1​09280