As governments and private companies race to put satellites into space, there will be an unprecedented demand to clean up dangerous debris. The main causes of space debris are collisions between satellites. For some perspective, 3200 non-operational satellites currently orbit Earth and around 12,000 satellites are expected to be launched as part of Starlink alone. Their purposes range from GPS to environmental monitoring in the Amazon and collectively, they are responsible for the smooth operations of all elements of our lives. However, the presence of debris threatens to cripple this critical infrastructure.
On February 1, 2003, the fatal crash of the Columbia space shuttle was due to a small piece of foam which punctured the left wing causing it to disintegrate during re-entry. At supersonic speeds, the momentum of a infinitesimally small object has potential to do a large amount of damage. The amount of debris that has been recorded is around 34,000 objects according to the European Space Agency. While plans have been made by governments to recover their decommissioned satellites, the vast majority of debris is still unaccounted for. Due to a domino effect named the Kessler Syndrome in the 1970’s, the number of space debris increases exponentially with the number of satellites or debris.
The main orbits for satellites are LEO and GEO however geosynchronous orbit is more common for telecommunication and weather monitoring. The main question is “Why is debris in these regions dangerous to satellites” ?
It turns out that the velocity of satellites around an elliptical orbit can reach 8 km/s at the periapsis which is about 23 times the speed of sound. With such high speeds, it is predictable that they can deal a great amount of damage upon collision. If a piece of metal has a mass of just 4 g, its momentum becomes 32 kg m/s or 10 times that of a firearm. And while telescopes can track the movement of larger decommissioned satellites, they do not have the capacity to track anything under 10 cm³ or smaller.
Part 1: Mapping and Capturing debris
While conventional solutions might involve a robotic arm like one implemented by the Canadarm on the ISS, the compact size of the debris raises technical challenges for their collection. The first part of the solution involves a probe consisting of an electromagnet, net, CPU, and camera. The onboard computer is trained using a CNN to detect high level features such as debris or satellites. The method for this classification is YOLO3 which creates bounding boxes around objects then predicts what object it is. The main advantage of YOLO3 is the real-time processing which is around 45 frames per second. Classifying objects is necessary to determine whether it will be magnetic or not.
As a whole, most of the debris in space is a group of metals due to their durability such as aluminum, lithium, nickel however certain plastics or carbon composites are non-magnetic and therefore difficult to retrieve. First it is necessary to calculate the amount of force required to accelerate a piece of debris. This can be modelled by the Lorentz Equation and then equating to mass x acceleration.
The acceleration should be around 5 m/s which would is sufficient to overcome it’s inertia. Since there is no drag, objects are able to accelerate rapidly which is why the acceleration is relatively small.
Next, the magnetic field(B) can be substituted into Ampere’s Law to get the current required. It is also necessary to fix the number of coils to around 30,000 because of the diminishing returns as the thickness and resistance of wire increases.
The current is powered by an array of solar panels which are common in most satellites; the added benefits of reduced distance from the sun increases the amount of energy available. Note that the trash-cleaning satellites are only operational when they are facing the sun.
Part 2: Storing debris
As you may know, the atmosphere evaporates medium-sized meteorites and rocks by burning them at temperatures close to 1650 ºC. Since the collected debris is uneconomic to be recycled, the most logical option would be to send the satellite into the atmosphere and evaporating the debris. At it’s size(125,000 cm³), it will have sufficient mass to impact the surface of Earth. However, if it does, the parts will land in the middle of the ocean.
At the end of the trash satellite’s lifespan(20 years), it will use it’s remaining energy to power an electric thruster to reach a Low Earth Orbit where it will eventually spiral into the atmosphere. This method of propulsion has been used for decades and has the ability to apply a thrust over time. In the worst case scenario, the satellite is fortified so that it will not turn into space debris.
Economics of the plan
One question that people commonly ask is about the market for this satellite when cleaning up space benefits everybody and not an individual entity. The answer is that the financial risk from collisions with debris far exceeds the price to clean it up. It is estimated that the space industry will exceed $1.3 trillion USD by 2030 led by market players such as SpaceX, Boeing, and Blue Origin. From this market report, satellites are estimated to account for 50% of the growth either in industries such as military or telecommunications. The cost per satellite is around $250,000 and the probability of collision increases as more satellites are launched into space.
This does not take into account the price of space shuttles which is around $450 million at the moment and $7 billion for the Columbia mission. From this, it becomes clear that private organizations have a financial incentive to protect their investments in space. Governmental bodies like NASA/ESA/CNSA also have interests in the cleanliness of space as scientific instruments like the Hubble Space Telescope are threatened by space debris.
Cost to build
The main cost is the cost to launch the satellite into space. For a cube sat of this size, the price is around $250,000 at $5,000/kg.
Next, the cost of raw materials is primarily the metal core in the electromagnet, heat shielding, and solar panels. The estimated cost of this is as follows.
The final cost of every mission is around $500,000 with a 20% additional budget for defective equipment and contingencies. It is likely that this will become more affordable over time due to
1. Reduced cost/kg
2. Increase in electric battery efficiency and longevity along with decrease in cost
3. Scalability by sharing parts, resources, personnel
The Future of HighSeas
As an organization, our work not only prevents the buildup of debris, it saves lives. Some next steps to take are finalizing the costs of materials and rigorously testing the electromagnet.
If you would like to learn more
- Check out our website
- Read our scientific paper
If you have any questions, feel free to reach out through LinkedIn.