There's hardly an aspect of life that doesn't rely to some extent on satellites. From weather forecasts to satnavs to get us somewhere (even when we know the way), when we listen to radio, watch Netflix, make a mobile phone call, when we shop online, in all those cases there's a good chance that some of the data is transmitted via one of these metal boxes orbiting our planet. It follows that losing access to satellites is a significant issue.
Today, about 2,000 operational satellites are in orbit around the Earth. Last year alone, 86 launches placed more than 400 spacecraft into orbit, a number that is to grow substantially over the next decade. But it's not just satellites that fly around our planet.
The United States Strategic Command’s Space Surveillance Network (SSN), which detects, identifies and tracks artificial objects in orbit around the Earth, from an astronaut’s glove to dead spacecraft and disused rocket stages, has a public catalogue of roughly 20,000 items larger than 10cm. That means only ten percent are active satellites and 90% is junk. Let me say that again 90 percent is junk.
It gets worse though. The current estimate of objects larger than a marble orbiting Earth is 750,000. In addition, there are over 170 million items of debris too small to be tracked by the SSN but still large enough to threaten robotic missions and human spaceflight. Enough to make any astronaut a little nervous, I'd imagine. For a fantastic view of an animated realtime 3D map of objects in Earth orbit go to http://stuffin.space.
The largest objects aren't necessarily those that pose the greatest danger. In August 2016 a centimetre-sized particle hit one of the solar arrays on the European Space Agency's (ESA) Sentinel 1A satellite and produced a small reduction in power and a change in the spacecraft’s orbit and orientation. Sentinel 1A is part of ESA's Copernicus programme and will track many aspects of Earth's environment, for example oil spills, sea ice mapping sea ice and monitoring movement in land surfaces.
It's millimetre-sized orbital debris that have the highest penetration risk because of the high impact speed to most operational spacecraft in low-Earth orbit. These tiny fragments far outpace the punch of a bullet (the average bullet travels at just 2,700 mph) with maximum speeds reaching 48,000km/h. On collision at orbital velocity, a one centimetre speck of debris can have an energy that is comparable to an exploding hand grenade. Ergo, no object in space is benign.
And while generally speaking space is big, space around the Earth and in particular orbital space is not. Like cars use roads, satellites use orbits and just as some roads are more popular, so are certain orbits. Usually objects below 600km will be brought down by natural forces within 25 years, and burn up in the atmosphere – as the Chinese space lab Tiangong-1 did earlier this year after China lost control in 2016 – everything above needs an active mechanism to lower it.
According to the European Space Agency for many missions, space debris impact represents the third highest risk of losing a spacecraft. The other two are risks associated with launch and deployment in orbit. The US government logged 308,984 potential space-junk collisions in 2017. And the problem is likely to get much worse. In April this year, Dan Hart, Virgin Orbit president and chief executive acknowledged that until recently he 'didn’t see much of a business case for space debris removal, but that is changing with the number of satellites people plan to send into low Earth orbit'.
What everybody is worried about more than the collision itself, is the dreaded Kessler Effect or Kessler Syndrome, where one piece of debris hits another and another so that it becomes an unstoppable runaway disaster cascade, which in the end could make an entire orbit unusable for satellites. The loss of orbital access and of satellites would mean stepping back probably decades in terms of our technology that we taken for granted on Earth.
However, even if all space operators start reducing the creation of space debris right now, resulting in a better than business-as-usual scenario, we would still see a growth in space debris and risking a Kessler Effect. Based on its 2017 analysis revealing that the dangerous tipping point in terms of number of space debris has already been reached, ESA suggests that we need to remove massive objects from orbit, in particular, those that have the potential to fragment into smaller particles.
One of them is the European satellite Envisat, the size of a double decker bus, which stopped working in 2012. Since then it's been circling the Earth, threatening other key satellites in its path. In 2017 alone, the US government counted 308,984 close calls with space debris and issued 655 'emergency-reportable' alerts to satellite operators.
There have been two major space-debris events in the last decade or so. In 2007, the Chinese destroyed one of their weather satellites at an altitude of 865km using a missile launched from Earth. The satellite disintegrated into an estimated 150,000 pieces of additional space debris.
The second occasion was in 2009 when the Russian military satellite Cosmos-2251 and US commercial satellite Iridium 33 crashed into each other, producing more than 1,400 pieces of debris larger than 10 cm.
We don't even fully understand the physics of two satellites colliding. To find out, the European Space Agency is launching a new research project to study satellite collisions in space. Because it's not practical to add to the problem by smashing satellites in space (although I wouldn't be surprised if the guys from TopGear had some ideas around that), researchers will use data from previous crash events and modify it to simulate how satellites behave when they slam into one another. After these simulations, the researchers will turn to practical experiments to smash together 500 kg-scale satellites under lab conditions. The aim is to project the evolution of the debris environment for the next 200 years.
What is clear though is that with a predicted increase of more than tenfold the current payloads (forecasts foresee demand ranging up to 4,040 payloads per annum in 2036) being launched into low Earth orbit over the next twenty years the likelihood of further collisions is going up too. OneWeb is planning to send up over 2,000 satellites. In 2017 SpaceX submitted regulatory filings to launch a total of nearly 12,000 satellites to orbit by the mid-2020s, Boeing has filed for 1,396-2,956 satellites and Samsung announced a constellation of 4,600.
Clearly there is an increasing risk of space debris for existing and future missions, but what can be done to improve tracking of debris, how do we mitigate creating more space junk and how do we clean up the existing trash?
Tracking Space Debris
Tracking space debris is difficult but an essential first step. Before you can remove the trash you have to know where it is, and how it moves. It is an international effort that affects every space-faring nation and every mission. There are various public and private organisations that are tracking junk in space. Here are some examples.
Missions for active debris removal (ADR)
While it's important to know where the junk is, we also need to start removing it from Earth's orbit. Swalloing a spacecraft looked easy in the Bond film You Only Live Twice but in reality if a satellite is tumbling through space synchronising the approaching craft and then somehow capturing it is a more complex issue. Suggested mechanisms include using a robotic arm, net or harpoon. There are various ADR missions under way or planned for testing.
Mitigating space debris
As yet, there is no international law about the creation of space debris, only voluntary guidelines published by the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) in 2007. This in turn led to the voluntary ISO standard 24113:2011 on debris mitigation requirements. It's intention is to 'reduce the growth of space debris by ensuring that spacecraft and launch vehicle orbital stages are designed, operated and disposed of in a manner that prevents them from generating debris throughout their orbital lifetime'.
Economically speaking, there hasn't really been any incentive to do anything about it. In fact, industry and government have a robust financial incentive to launch satellites, but considerably less motivation to clean up the debris. If a significant threat arose, it’s usually possible to move a satellite out of the way. That’s much cheaper than actually clearing the junk. The growing number of satellite missions might change the economies though.
In the geostationary region, where you have a large amount of telecommunication and broadcasting satellites, nearly all of the operators at the end of their mission at least attempt to move their satellites out of the geostationary orbit. The rules have been there for nearly two decades and they are now considered in the design and operation of satellites.
For lower Earth orbits however, the majority of operators are still relying on gravity and the atmosphere to deorbit and burn up the satellites and related junk. This might be fine for up to say 500 or 600 kilometres, depending on the satellites. But for higher orbits or more massive objects, the number of satellites that perform an active deorbit burn is still not growing, and that is a matter of concern.
"Only about 60% of the satellites that should be disposed of at the end of their missions under current guidelines are, in fact, properly managed,” said Holger Krag, head of ESA’s debris office. Particularly with the announcement of large satellite constellations coming up, we have to increase our efforts to mitigate the creation of space debris. Both OneWeb and SpaceX for their Starlink constellation committed to a deorbit plan which will move the satellites into orbits where they will reenter the Earth's atmosphere within approximately one year following their end-of-life. OneWeb's CEO Greg Wyler also suggested to 'look to aviation air traffic control and the spacing between aircraft as a great model for how to deal with constellation collisions'.
Unsurprisingly, we haven’t yet found a way to use space sustainably. Unsurprisingly, because we haven't even found a way to use Earth's in a sustainable manner. It is imperative though that companies and governments eventually de-orbit any new things they launch in a controlled way.
Today, about 2,000 operational satellites are in orbit around the Earth. Last year alone, 86 launches placed more than 400 spacecraft into orbit, a number that is to grow substantially over the next decade. But it's not just satellites that fly around our planet.
The United States Strategic Command’s Space Surveillance Network (SSN), which detects, identifies and tracks artificial objects in orbit around the Earth, from an astronaut’s glove to dead spacecraft and disused rocket stages, has a public catalogue of roughly 20,000 items larger than 10cm. That means only ten percent are active satellites and 90% is junk. Let me say that again 90 percent is junk.
It gets worse though. The current estimate of objects larger than a marble orbiting Earth is 750,000. In addition, there are over 170 million items of debris too small to be tracked by the SSN but still large enough to threaten robotic missions and human spaceflight. Enough to make any astronaut a little nervous, I'd imagine. For a fantastic view of an animated realtime 3D map of objects in Earth orbit go to http://stuffin.space.
The largest objects aren't necessarily those that pose the greatest danger. In August 2016 a centimetre-sized particle hit one of the solar arrays on the European Space Agency's (ESA) Sentinel 1A satellite and produced a small reduction in power and a change in the spacecraft’s orbit and orientation. Sentinel 1A is part of ESA's Copernicus programme and will track many aspects of Earth's environment, for example oil spills, sea ice mapping sea ice and monitoring movement in land surfaces.
It's millimetre-sized orbital debris that have the highest penetration risk because of the high impact speed to most operational spacecraft in low-Earth orbit. These tiny fragments far outpace the punch of a bullet (the average bullet travels at just 2,700 mph) with maximum speeds reaching 48,000km/h. On collision at orbital velocity, a one centimetre speck of debris can have an energy that is comparable to an exploding hand grenade. Ergo, no object in space is benign.
And while generally speaking space is big, space around the Earth and in particular orbital space is not. Like cars use roads, satellites use orbits and just as some roads are more popular, so are certain orbits. Usually objects below 600km will be brought down by natural forces within 25 years, and burn up in the atmosphere – as the Chinese space lab Tiangong-1 did earlier this year after China lost control in 2016 – everything above needs an active mechanism to lower it.
According to the European Space Agency for many missions, space debris impact represents the third highest risk of losing a spacecraft. The other two are risks associated with launch and deployment in orbit. The US government logged 308,984 potential space-junk collisions in 2017. And the problem is likely to get much worse. In April this year, Dan Hart, Virgin Orbit president and chief executive acknowledged that until recently he 'didn’t see much of a business case for space debris removal, but that is changing with the number of satellites people plan to send into low Earth orbit'.
What everybody is worried about more than the collision itself, is the dreaded Kessler Effect or Kessler Syndrome, where one piece of debris hits another and another so that it becomes an unstoppable runaway disaster cascade, which in the end could make an entire orbit unusable for satellites. The loss of orbital access and of satellites would mean stepping back probably decades in terms of our technology that we taken for granted on Earth.
However, even if all space operators start reducing the creation of space debris right now, resulting in a better than business-as-usual scenario, we would still see a growth in space debris and risking a Kessler Effect. Based on its 2017 analysis revealing that the dangerous tipping point in terms of number of space debris has already been reached, ESA suggests that we need to remove massive objects from orbit, in particular, those that have the potential to fragment into smaller particles.
One of them is the European satellite Envisat, the size of a double decker bus, which stopped working in 2012. Since then it's been circling the Earth, threatening other key satellites in its path. In 2017 alone, the US government counted 308,984 close calls with space debris and issued 655 'emergency-reportable' alerts to satellite operators.
There have been two major space-debris events in the last decade or so. In 2007, the Chinese destroyed one of their weather satellites at an altitude of 865km using a missile launched from Earth. The satellite disintegrated into an estimated 150,000 pieces of additional space debris.
The second occasion was in 2009 when the Russian military satellite Cosmos-2251 and US commercial satellite Iridium 33 crashed into each other, producing more than 1,400 pieces of debris larger than 10 cm.
We don't even fully understand the physics of two satellites colliding. To find out, the European Space Agency is launching a new research project to study satellite collisions in space. Because it's not practical to add to the problem by smashing satellites in space (although I wouldn't be surprised if the guys from TopGear had some ideas around that), researchers will use data from previous crash events and modify it to simulate how satellites behave when they slam into one another. After these simulations, the researchers will turn to practical experiments to smash together 500 kg-scale satellites under lab conditions. The aim is to project the evolution of the debris environment for the next 200 years.
What is clear though is that with a predicted increase of more than tenfold the current payloads (forecasts foresee demand ranging up to 4,040 payloads per annum in 2036) being launched into low Earth orbit over the next twenty years the likelihood of further collisions is going up too. OneWeb is planning to send up over 2,000 satellites. In 2017 SpaceX submitted regulatory filings to launch a total of nearly 12,000 satellites to orbit by the mid-2020s, Boeing has filed for 1,396-2,956 satellites and Samsung announced a constellation of 4,600.
Clearly there is an increasing risk of space debris for existing and future missions, but what can be done to improve tracking of debris, how do we mitigate creating more space junk and how do we clean up the existing trash?
Tracking Space Debris
Tracking space debris is difficult but an essential first step. Before you can remove the trash you have to know where it is, and how it moves. It is an international effort that affects every space-faring nation and every mission. There are various public and private organisations that are tracking junk in space. Here are some examples.
- The leading organisation for tracking space debris is the above mentioned SSN which uses a global network of public and private partners to identify, track, and share information about objects in space. The SSN supercomputers constantly check the orbits of all satellites and known bits of space junk to see if there's any risk of future collision days in advance.
- One of the most recent additions is Seer Tracking. Developed by nineteen year old Amber Young, Seer Tracking uses artificial neural networks (ANNs) to determine orbital patterns of clouds of space debris, debris classification and provide orbital predictions days in advance. Astonishingly, she started to write the software when she was 15 and finished a first version in 2016 when she got her network to make predictions three days ahead with 98% accuracy. Far more accurate than the statistical models developed by NASA.
- In the UK, Damage, draws in information of launches and spacecraft from different space agencies, and uses the data to illustrate the low Earth orbit and geosynchronous orbit regions in as much detail as possible. The UK Space Agency has used the computer model since 2004, allowing them to understand what impact new space systems might have on their environments.
- NASA’s Space Debris Sensor orbits the Earth on the International Space Station. The sensor, a one-metre-square bit of kit around 20cm thick, was attached to the outside of the space station in December 2017. It will detect millimetre-sized pieces of debris for at least two years and will determine whether the impacting object is from space or a man-made piece of space debris.
- The Aerospace Corporation is working alongside Lockheed Martin to develop a tracking system known as a space fence, which aims to detect debris in more detail using radar. Another area being looked into by the Aerospace Corporation involves implanting new satellites with transponder packages and reflectors to make it easier for radar to pick up these small objects.
- Russia’s space agency has signed an agreement to install a new debris-tracking telescope in Brazil.
- The Deimos Sky Survey in Spain uses a network of telescopes to detect and track near Earth objects such as asteroids as well as space debris, including Elon Musk’s car in space.
Missions for active debris removal (ADR)
While it's important to know where the junk is, we also need to start removing it from Earth's orbit. Swalloing a spacecraft looked easy in the Bond film You Only Live Twice but in reality if a satellite is tumbling through space synchronising the approaching craft and then somehow capturing it is a more complex issue. Suggested mechanisms include using a robotic arm, net or harpoon. There are various ADR missions under way or planned for testing.
- On 4th April, SpaceX carried on a resupply rocket an experimental payload, two RemoveDebris spacecrafts, developed by the Surrey Space Centre at the University of Surrey to the International Space Station. Four key technologies will be tested on controlled objects: a visual navigation system, a net and a harpoon the size of a pen used to capture debris and a de-orbit sail use to slow the debris so it falls into the Earth’s atmosphere. Removing controlled objects is one thing however; using technologies on uncontrolled pieces of debris is another. For that ESA is also proposing a mission called e.deorbit at the end of 2019 to demonstrate that it's possible to remove an uncontrolled object safely from orbit.
- Astroscale wants to build a retrieval mechanism into spacecrafts before they launch. Should a satellite fail prematurely — and about 5 percent or more likely will — an Astroscale spacecraft would launch to snag the derelict satellite using the built-in component and dispose of the satellite. The current plan is to use one retrieval craft per piece of debris. While a reusable chaser spacecraft would be ideal, it isn't yet economically viable to change velocity required for capturing debris, bringing it to a lower orbit where it would degrade and then going back to hunt for more debris. In 2019, Astroscale will launch a mission called ELSA-d, which stands for End-of-Life Service by Astroscale-demonstration.
- British firm Hempsell Astronautics has proposed a system dubbed Necropolis that would collect defunct geostationary satellites and deliver them to a single spot in the so-called 'graveyard orbit'. This area is situated a few hundred kilometres above the roughly 22,000-mile-high (36,000 km) geostationary ring.
- D-Orbit is developing a solid-propellant technology for the commissioning and decommissioning of satellites.
- Launchspace Technologies proposes sending platforms the size of football fields into equatorial low Earth orbit to sweep up space debris ranging in size from one millimetre to five centimetres. The units with replaceable, mesh 'Debris Impact Pads' would clean up debris as it crosses the equator, while steering clear of satellites and debris large enough to track. The platforms, equipped with sensors, could also help the U.S. government to detect and track orbiting satellites and debris.
- A team from the University of Colorado Boulder envisions pushing defunct spacecraft away from the crowded geostationary ring without even touching them. This concept would use a 'pulsed electron gun', an intermittent electron beam of several tens of watts of electrical power.
- JAXA (Japan Aerospace Exploration Agency) suggests using electrodynamic tethers to remove spent rocket stages from LEO (rocket upper stages account for 18 percent of all tracked objects in Earth orbit, experts have said.) JAXA's claims that because of these objects' smooth and regular shapes, compared to satellites, they represent an ideal target for early removal attempts. However, JAXA's experimental system in which a long cable was supposed to be deployed from the Kounotori 6 satellite and once attached the tether would slow down the object, forcing it to re-enter into Earth’s atmosphere where it would burn up. Sadly, the tether didn't deploy properly from Japan's HTV-6 International Space Station resupply spaceship.
- Louis Wei-yu Feng, a student at the University of Cape Town in South Africa envisions a spacecraft fitted with 'shape memory alloy tentacles' that could collect and dispose of cubesats scattered around Earth orbit. The tentacle hand, dubbed MEDUSA, is made of nitinol, a material that can switch from molten to solid state multiple times, giving the collector spacecraft countless chances to grasp an out-of-control tumbling cubesat.
- With a total of €2.8m in funding from the Horizon 2020 programme, a team at Strathclyde University led by Airbus Defence and Space will carry out initial research under the TeSeR programme (Technology for Self-Removal of Spacecraft) for the development of a prototype of a cost-efficient but highly reliable removal module.
Mitigating space debris
As yet, there is no international law about the creation of space debris, only voluntary guidelines published by the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) in 2007. This in turn led to the voluntary ISO standard 24113:2011 on debris mitigation requirements. It's intention is to 'reduce the growth of space debris by ensuring that spacecraft and launch vehicle orbital stages are designed, operated and disposed of in a manner that prevents them from generating debris throughout their orbital lifetime'.
Economically speaking, there hasn't really been any incentive to do anything about it. In fact, industry and government have a robust financial incentive to launch satellites, but considerably less motivation to clean up the debris. If a significant threat arose, it’s usually possible to move a satellite out of the way. That’s much cheaper than actually clearing the junk. The growing number of satellite missions might change the economies though.
In the geostationary region, where you have a large amount of telecommunication and broadcasting satellites, nearly all of the operators at the end of their mission at least attempt to move their satellites out of the geostationary orbit. The rules have been there for nearly two decades and they are now considered in the design and operation of satellites.
For lower Earth orbits however, the majority of operators are still relying on gravity and the atmosphere to deorbit and burn up the satellites and related junk. This might be fine for up to say 500 or 600 kilometres, depending on the satellites. But for higher orbits or more massive objects, the number of satellites that perform an active deorbit burn is still not growing, and that is a matter of concern.
"Only about 60% of the satellites that should be disposed of at the end of their missions under current guidelines are, in fact, properly managed,” said Holger Krag, head of ESA’s debris office. Particularly with the announcement of large satellite constellations coming up, we have to increase our efforts to mitigate the creation of space debris. Both OneWeb and SpaceX for their Starlink constellation committed to a deorbit plan which will move the satellites into orbits where they will reenter the Earth's atmosphere within approximately one year following their end-of-life. OneWeb's CEO Greg Wyler also suggested to 'look to aviation air traffic control and the spacing between aircraft as a great model for how to deal with constellation collisions'.
Unsurprisingly, we haven’t yet found a way to use space sustainably. Unsurprisingly, because we haven't even found a way to use Earth's in a sustainable manner. It is imperative though that companies and governments eventually de-orbit any new things they launch in a controlled way.
