THE CHALLENGE

Our challenge aims to design a mission to clean the oceans from the so-called "Oceanic garbage patches" which are collections of marine debris that come together due to surface currents, more specifically to formulate some key technologies, procedures, and approaches to be used in a mission to help clean up oceanic garbage.

TODAY'S SYSTEMS

Today'scollecting systems that are dealing with the problem, use largemerchant ships to collect the garbage as they find it floating in the ocean, using fishing nets that are often lost, increasing the waste.

Somecompanies use long buoyants adrift along the currents to collect largewastes. These are then reached by heavy cargo ships, that leave fromthe land, in order to be sorted and disposed of.

However,this method uses large quantities of fossil fuels to move the shipsfrom the land to the collection points each time, not to mentionthat since the waste is not being compacted, the ships findthemselves filled mainly with volumes of air.

Ifthere is some hope that countries around the world will stopproducing all the 100 million tons of plastic every year (of which10% end up in the ocean), a long-term solution is anyway needed toremedy the damage already done and those that will still be done.

OUR APPROACH

In order to consider all the possible aspects related to such a large mission, we started by drawing up a list of the goals that have to be achieved and the issues to be put into play:

• where our action would have the greatest positive effects
• which type of debris do we want to focus on
• how can we collect such type of debris
• what are the most effective way to reach the target destination
• how can we provide the system a sufficient lifetime so it can be used to clean the six major Oceanic Patches
• what can we use to reduce climate impact and the use of fossil fuels

Starting from these questions we did some research about the seriousness of the situation (sources in the bibliography) and the data we have reached is quite alarming.

Considering the worst case in order to be prepared for it, we found that:

• 100*10^3 animals are killed or injured every year due to oceanic waste
• the mass of the Great Pacific Patch (the biggest in the world) is about 100*10^6 kg
• the surface that it covers is 1.6*10^6 square kilometers
• its volume is approximately 100^10^3 cubic meters
• every year the world dumps in the ocean 10% of a total of 100*10^6 tonns of garbage.

Given these considerations we are now ready to formulate our solution.

THE "ISLAND"

The first factor that must be taken into consideration is the distance from the land of the Patch, certainly disadvantageous from the point of view of energy saving.

What can we do to minimize ship routes?

The mission we have planned involves bringing a semi-mobile barge to the "center" of the Patch that can act as a temporary island of suction, sorting, compacting and stocking.

But where should we position it so that the routes are really reduced to a minimum? The answer is provided by elementary geometry.

The patch has an elongated shape along the path of the currents, therefore it is not possible to identify a single center from which we can make the ships leave: they would make longer journeys than necessary.

But if we approximate the shape of the patch to an ellipse we are given the solution: since the barge is a semi-mobile platform we can position it first on one focal point and then on the second.

The second benefit that a semi-permanent platform in the middle of the patch would bring is that, if it is large enough, it can act directly as a filtering and compactation station, using the abundance of renewable energy sources that we find in the midst of the oceans at points of strong current.

Such energy sources are for example:

• water flow from medium to high depth ocean currents (so as to avoid plastic jams)
• strong constant oceanic winds which are also the cause of surface currents
• solar energy coming both from above and reflected from the water surface.

COLLECTING WASTE

The island, as it was conceived, will also act as a collection and filtering station for the waste that will be supplied by the two tugs.

These two, through the use of large U-shaped buoyants collecting the waste from the outer edge where the density is lower, will take the outer trash to the island.

The usefulness of putting the station at the focal points of the ellipse, as well as clearly reducing the length of the routes, is that these are the points of true accumulation of waste. In this way, even decreasing the length of the routes to a fraction of what is the distance from the outer edge, the ocean itself will bring the rest of the waste closer to the island, continuing to accumulate it following a spiral route.

Once the waste has accumulated around the island, a series of hatches will expose the pumps to the ocean, which will suck up the plastic waste inside the filtering stations.

THE FILTERING METHOD

The filtering process we designed for the island consists of 3 main stages:

1. Theentry of water through the aid of auxiliary pumps is a process thatgenerates strong turbulence. For this reason thefirst stage will be a settling tank, so that large waste can separate from the rest and remain at the surface, while fragments and fauna will stay under the water. This huge first tank will also be equipped with infrared morphological recognition sensors, so as to be able to signal the presence of large cetaceans, endangered species or trapped workers
2. At this point, once we have ascertained that there are no endangered organisms inside the tank, we can remove the surface layer of garbage and leave only the small fragments of mixed plastics in the tank, which will simply be compacted once the water has dried up in the tank.
3. The final stage involves the simple separation of the different plastics taking advantage of their different density.

COMPACTION AND STOCKING

The last innovation we wanted to provide to the barge is the waste compaction station, so as to avoid unnecessary air-laden routes back and forth from the land.

Performing simple calculations starting from the data we highlighted at the beginning of the presentation, knowing the average density of the plastic and making some downward estimates (always in the worst case scenario) we found that, if compacted even to only half of their original volume , the waste of the entire Great Pacific Garbage Patch could be transported inside two common cargo ships, which will the stocking capacity of the island.

BIBLIOGRAPHY

https://svs.gsfc.nasa.gov/4174

https://2019.spaceappschallenge.org/challenges/earths-oceans/trash-cleanup/detail

https://www.nationalgeographic.com/news/2018/03/gr...

https://theoceancleanup.com/great-pacific-garbage-patch/