This is a straight to the point explaination of the space debris problem. It will be updated regularly to include more information and different points of views.
Space debris does not affect most of us as directly as plastic or air pollution. Most of us aren't even aware of it. We are becoming increasingly dependent on satellites. From live TV to communications, navigation to helping farmers grow better crops, tracking ships and planes to tracking illegal fishing and tracking pollution, the usecases are growing every day!
Going to space isn't only about exploring Moon, Mars, or the Solar system - it's also about making Earth a better place to live.
This is why we should all care about space debris.
What is space debris?
Generally speaking, space debris is the used spacecraft or rocket parts floating around uncontrolled around the Earth orbit. These can be as small as nuts, bolt, or springs used for stage separation in rockets and solar panel deploying mechanisms, or spent rocket booster stages as big as a double decker bus.
Dead or de-commissioned satellites are also a major source of new space debris. These are becoming a big problem very, very fast.
Earth orbit basics
Before moving on, here is some basics about Earth orbits necessary to understand the space environment in Earth orbit.
There are three (circular) orbits I’ll commonly refer to in this guide;
low Earth orbit (LEO)
medium Earth orbit (MEO)
geostationary or geosynchronous orbit (GEO or GSO)
There are others such as elliptical or heliocentric orbits, but for now let’s keep it simple and ignore these.
Even at a several hundred kilometers of altitude above the Earth, there is still some atmosphere. This means objects experience aerodynamic drag. This drag will eventually slow the speed of objects in space and eventually fall back to Earth (very, very fast). Big objects will breakup into smaller pieces, and small ones will burn up when it re-enters the Earth’s thicker atmosphere.
We call this darg-induced loss of altitude ‘orbital decay’.
Orbital decay affects satellites more in LEO than other higher orbits. Objects in LEO can take between a few years to a few decades to re-enter the Earth atmosphere. For higher altitude orbits (MEO, GEO), this is hundreds to even thousands of years.
Satellites and Space Debris
Since Sputnik (1957), we have been launching satellites (and humans) into Earth orbit and beyond. Here’s a chart showing satellite launches per year between 1990 and 2019.
Between January to March 2020 (not shown above), 343 satellites were launched – nearly the same amount launched as in the entirety of 2017.
This growth is a huge sustainability challenge.
Why is Space Debris a problem?
The increase in amount of satellites launched naturally brings with it an increase in debris generated. Here is a chart from the European Space Agency showing how the amount of objects (and debris) in Earth orbit has increased over time.
Another chart below shows the distribution of debris by altitude for LEO. Most of debris is situated around 700-800 km altitude.
Collisions create more debris. In 2007, the Chinese government successfully destroyed their own weather satellite to test their anti-satellite (ASAT) missile. This ASAT test created over 3,000 new pieces of debris. In 2009, an active Iridium-33 commercial satellite was hit by a defunct Russian military satellite (Kosmos 2251) at an altitude of 776 km. This resulted in an estimated 2,300 debris fragments that are trackable.
This information is shown in the chart below (Source: SW Foundation). This data is taken from US Space Surveillance Network presented in Orbital Debris Quarterly News April 2020.
The Kessler Syndrome
In 1978, NASA scientist Donald Kessler along with Burton Cour-Palais published a paper titled ‘Collision Frequency of Artificial Satellites: The Creation of a Debris Belt’. This paper predicted that as the number of objects orbiting the Earth increase, the probability of collisions between them also increase, leading to a cascade of even more collisions and debris, further increase the probability of future collisions. This was later referred to as the ‘Kessler Syndrome’ (or the Kessler Effect).
After a collision, the field of debris evolves and spreads rather than staying localized. Images below show a simulation of a debris field from an anti-satellite missile such as the one by China in 2007.
The space debris mitigation guidelines
In 2002, the Inter-Agency Debris Coordination Committee (IADC) was formed with the intention to adopt a common set of guidelines designed to mitigate the growth of orbital debris population. It currently comprises of 13 agencies from around the globe.
The space debris mitigation guidelines were adopted in 2007. These guidelines stipulate steps that should be taken by satellite operators to minimize chances of increasing debris is the space environment. A couple of key guidelines include:
Satellites in LEO have to be decommissioned at an orbit where it will re-enter and burn up in the atmosphere within 25 years – this typically tends to happen when satellites are decommissioned and placed at 500 km or lower altitudes.
Satellites, or other space objects must not have stored energy – this means that fuel tanks, which typically have explosive fuel must be emptied as much as possible.
The problem with these guidelines is that they’re guidelines, not regulations. What does this mean? I’ll let the Head of Orbital Debris office at NASA, J.C. Liou explain:
“Fewer than half of global space operators comply with the current 25-year deadline for disposal of dead satellites, contributing to the ever-growing amount of junk littering space and putting active satellites in danger”
This 25-year rule has been criticized time and again, but as J.C. Liou explains, “the benefit of reducing the 25-year rule to five years is not very significant”.
The graph below shows what J.C. Liou means. It illustrates the estimated increase in non-functioning satellites in LEO up until 2030 considering de-orbit times between 2-years to 25-years. How this graph was made is shown here as part of my earlier post on space junk.
New Regulations and Incentives
Implementation of new guidelines and regulations is a hotly debated topic.
The U.S. Government updated their government guidelines, “Orbital Debris Mitigation Standard Practices” in December 2019. A couple of notable changes are:
No more than 1 in 1,000 chance of a debris creating an explosion for a satellite or a rocket upper stage.
For large constellations of satellites (more than 100), each satellite must have a >90% chance of successful disposal (usually means de-orbit back to Earth’s atmosphere), with a goal of 99% or better.
The Federal Communications Commission (FCC) in the US is also introducing stricter regulations. These are often criticised by the industry and other stakeholders. These are likely to include the following rules amongst others;
Satellite constellations must have a collective collision risk of 1 in 1,000. This is a big change from NASA’s standard of 1 in 1,000 risk for individual satellite.
New satellites operating above 400 kms will require a propulsion system or other means of collision avoidance – a change from 600 kms standard.
Another incentive is the ‘Space Sustainability Rating’ – or SSR. It’s a concept developed by the World Economic Forum’s Global Future Council on Space Technologies. Here’s how it is described by the Council:
“The Space Sustainability Rating (SSR) will provide a new, innovative way of addressing the orbital challenge by encouraging responsible behaviour in space through increasing the transparency of organizations’ debris mitigation efforts. The SSR will provide a score representing a mission’s sustainability as it relates to debris mitigation and alignment with international guidelines.”
These regulations and incentives are tricky since they only work well if all parties abide by them.
Debris Tracking Technologies
Coming Soon!
Debris Removal Technologies
Coming Soon!
That’s it for now! I will be updating and improving this post over time with more detailed information.
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