Old Satellites and Space Junk: Potentials for Re-Use and Recycling
by
Dr. Bassem Sabra
for
Orbital Index
August 21, 2021
Space around Earth – from the edge of its atmosphere of few hundred kilometers to tens of thousands of kilometers – is teaming with tens of thousands of defunct satellites and spacecraft parts that have outlived their missions. These artificial space objects are basically just orbiting Earth forever, or until their orbits decay to a point where they burn upon their re-entry into Earth’s atmosphere. They pose a collision hazard to the other useful satellites out there. The collision threat has a multiplier effect: not only does it damage a functioning satellite, but it also creates further debris that in turn will increase the chance of additional collisions with other satellites. This cascading catastrophe is known as the Kessler effect, in honor of the NASA scientist who first dreamt up this nightmarish scenario. As space waste in low earth orbit (LEO, altitude of about 2000 kilometers) increases, collisions lead to further collisions that lead to more collisions, etc. making outer space inaccessible as early as 2040 should this runaway collision avalanche come to pass!
One possible way to mitigate space debris is to look at it from a profit angle. However, with talk of profit comes legal worries. Is space debris free for all to capture, process, reuse, up-cycle, recycle? Does it have an owner? I attempted to answer these questions by conducting a short legal study (WhoOwns Old Satellites and Space Junk?) In a nutshell, one has to make a distinction between space debris (rocket parts, pieces of metal, etc.) and defunct satellites. Space debris has no owner, and under space law it cannot be reclaimed. However, defunct satellites are free to be reclaimed if one can prove that their original owners abandoned them. Up-dates to the United Nations Outer Space Treaty are needed in order to open up space debris to “prospecting.”
I then searched website for space debris and defunct satellites. A list of all defunct satellites in orbit was taken from celestrak.com. I also built an excel file that contains a list of satsin disposal/graveyard orbits. I took it from the UN Space Object Index https://www.unoosa.org/oosa/osoindex/search-ng.jspx?lf_id= . The celestrak file is more complete than the UNSOI. The celestrak is taken from a much larger file that includes more than 48,000 space objects. It is up-dated daily - most probably it will out-dated by the time I send you this msg. Taking this master file we can sort/search/etc on various columns and rows to answer the questions that might have. For example, we can select defunct sats in LEO. These are truly abandoned by the legal definition. Another useful website is space-track.org. A nice visualization website (that take space-track data) is https://maps.esri.com/rc/sat2/index.html.
I then sorted the defunct sats list on on perigee. Perigees less than 1000km are LEOs. I then created a listof satellites with optics (astro missions or Earth observing missions) and also created another list of communicationsats. I also created a massbudget of typical satellites:
It shows percentages of the sat's mass for each subsystem. Different subsystems are predominantly made up of different raw materials. For example, the structure of any sat is aluminum and titanium alloys. It is about 11-12% of the mass of a satellite. If there are for example about 1000 tons in defunct sats then about 110 tons are in aluminum and titanium alloys. I divided the sats into categories and estimated the average masses of the subsystems. Different subsystems are composed of primarily different raw materials. The thermal foil is NOT gold. It is kind of polyester film (gold-like in color) over a thin aluminum wire mesh. Heat pipes are mostly aluminum.
Further work allowed me to up-date my excel file to include spreadsheetsfor satellites by type. It gives the amount of material in each subsystem for a satellite of a given type (Earth observing, communication satellite, and astronomy satellite). The most common material is metal alloys (alloys of aluminum, titanium), gallium arsenide/etc (solar cells), nickel and lithium (batteries), special plastics, etc. There are a literally thousands upon thousands of materials approved by NASA for use in space.
It is important to keep in mind that the spreadsheets are estimates at best. The situation is even more complicated than finding out the typical materials available in a car - cars are mass produced. On the other hand, each and every satellite is one of a kind! Communication satellites are the closest thing that come to mass production. The only way to know exactly the ingredients in a given satellite is to first identify that particular satellite and then get subsystem info from the manufacturer, who will have to track down the sub manufacturers, etc. In my humble opinion, recycling satellites should focus on relatively one-type subsystem (the structure itself), solar cells, batteries, antennas, thermal insulation (aluminum and mylar), thrusters (high temperature resistant material) and payloads (cameras, spectrographs, sciency stuff that could be re-used). All the rest should be ground up and used for 3D printing or used as reaction mass in some novel propulsion system.
My hunch is that it is still not economically viable to recycles space debris and abandoned sats. However, upcycling (refurbishing and giving it a new mission) is definitely viable. A numerical model will help shed light on all of the relevant questions in your original description. One big unknown to keep in mind is in-space recycling. This so far is not existent and consequently there is not data on its economics. The difficulty is putting an estimate on on-orbit recycling. I contacted Neumann Space to inquire about cost of recycling into fuel. Unfortunately, the company didn't reply back. I put my own guesses and calculated accordingly.
The result is a spreadsheet that shows the evolution of the cost of launching in 1 kg to LEO versus the cost of recycling 1 kg in LEO (processing metal alloys to fuel rods, for example), all in 2020 US dollars. I assumed that the cost of recycling now is about 36 times that cost of launch and the recycling cost drops by 20% every year. With costs decreasing at their current rates recycling should become more profitable after 2050. My recycling estimates are based on my various readings and the hunches I developed while reading, and I read a LOT. Kindly note, as I stated previously, as off yet there is no real recycling in orbit and therefore there are no real cost estimate for that. Neumann Space did not respond. The following are the papers that I relied on the most:
"On-Orbit Manufacturing and Assembly of Spacecraft," Boyd et al. (2017), Institute of Defense Analysis paper.
2) "The Economics of the Control of the Space Debris Environment," Wiedemann et al. (2013), in Proc. of the 6th European Conference on Space Debris
3) "Theoretical Studies on Space Debris Recycling and Energy Conversion Systems in the ISS," Mariappan et al (2020), Engineering Reports
4) "The Economics of the Space Debris: Estimating the Costs and Benefits of Debris Mitigation," Macauly (2015), Astronautica
Re-use of communication satellites in GEO is already being pursued (MEV missions) and there is already an economic case for giving communication sats a new lease on life: Intelsat (owner of Intelsat 901) will pay Northup Grumman 13 million USD/year for 5 years to have MEV-1 attached to Intelsat 901. This comm sat would have cost 500 million USD to replace.
The space waste (defunct satellites and space debris) as a resource requires work on all fronts: legal, technological, and financial. International treaties and laws have to be up-dated in order to set standards for work in orbit. Technological advances must be achieved in order to create recycling plants in orbit. And, of course, all this requires initial financial investments. Governments could provide incentives, seed money, and the legal grease, but this activity is best carried out by private actors bent on profit. That is the only way to get things done: done fast and properly.
