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| Fig. 1: SpaceX Falcon 9 Rocket Pictured (Source: Wikimedia Commons) |
With the rise of mass consumerism and single-use plastics, waste production has continued to increase year after year. The UN estimates that 2.1 billion tonnes of garbage is produced each year. [1] This has created logistical challenges and caused severe ecological harm as garbage dumps continue to require greater land allocation, displacing vital ecosystems and leeching hazardous chemicals into our aquifers. One proposed solution is to launch garbage into space as a method of permanent disposal.
Most space-bound objects are launched into low Earth orbit, roughly 400 miles above Earth's surface. Garbage injected into this region of space would be extremely hazardous, both as a collision risk to the existing satellite constellations, and a risk to Earth. [2] Sparse gas particles inflict drag forces on satellites in this region, which causes objects to eventually fall back into Earth. Satellites in low Earth orbit thus have a finite lifetime before reentry. Garbage must therefore be ejected beyond Earth's gravitational pull, where there is no risk of reentry or collision with manmade satellites.
The cheapest launch vehicle available today is the SpaceX Falcon 9 rocket (See Fig. 1), which is capable of carrying a 2631 kg (5,800 lb) payload to geostationary orbit (a good approximation for gravitational escape) at a cost of approximately $62 million per flight. [3] The Falcon 9 rocket carries 91,243 kg (29,500 gallons) of RP-1 propellant, which has an energy density of 43 MJ/kg. [4,5] Based on this approximation, the Falcon 9 spends 3.92 TJ per launch and the energy cost to bring a kilogram to orbit is 1491 MJ/kg (414 kWh/kg) or 34.68 kg of RP-1 per 1 kg garbage.
Diverting current production of landfill-bound garbage to space would require approximately 8.7 × 1014 kWh or 3131 EJ (1 EJ = 1018 J) annually. Global energy consumption in 2022 is estimated at 595 EJ or 165,000 TWh annually. [6] Therefore, garbage disposal via space launch would require a five times increase in global energy production, not including the energy costs associated with refining RP-1 and isolating and liquefying O2 gas.
RP-1 reacts with O2 to form significant amounts of CO2 and H2O according to the stoichiometric equation [5]
Using this equation, each kilogram of RP-1 creates 3.14 kg of CO2. With approximately 34.7 kg of RP-1 per kilogram of garbage, launching a kilogram of garbage would release approximately 109 kg of CO2 into the atmosphere. Launching 2.1 billion tonnes of garbage would release 229 billion tonnes of CO2, increasing global emissions from 34.7 GtCO2 to 263.9 GtCO2, or by approximately 7.5 times.
That said, rockets are incredibly fuel inefficient and perhaps alternative launch techniques could be employed such as a rail gun, which could accelerate an object on Earth to a velocity sufficient to escape Earth's gravity. Neglecting minor factors like air resistance and thermal ablation, the minimum energy required to bring an object to orbit is the change in gravitational potential energy from Earth's surface to a distance at which Earth's gravity is negligible. From Newtonian mechanics, the gravitational potential energy of an object of mass m is [7]
| Epotential | = | - | G m mEarth r |
Thus the change in gravitational potential energy per unit mass is
| Epotential m |
= | G mEarth Rsurf |
= | 6.25 × 107 J/kg | = | 17.36 kWh/kg |
where G = 6.67 × 10-11 Nm2/ kg2, mEarth = 5.97 × 1024 kg, and Rsurf = 6371 km. Based on this theoretical minimum, ejecting global garbage would demand 3.6456 × 1013 kWh/yr, 22.3 times less than Falcon 9 launch. This high-efficiency launch system would only increase global energy consumption by 21%, which could be achieved by constructing 17,000 250MW natural gas power plants and would cost $1.38 trillion USD in fuel at $38/MWh. [8]
If instead of launching all garbage, only highly hazardous nuclear waste were launched into space, costs still remain prohibitive. The standard approach to nuclear waste managment is deep underground burial, such as the proposed Yucca Mountain repository. Estimates place disposal costs between $148,000 and $1,041,000 per metric ton of heavy metal (MTHM). [8] Even at the upper limit of underground burial costs, nuclear waste disposal via space launch by Falcon 9 (≅$23.5 million per ton) would cost 22.6 times more than proven disposal methods.
While there may not be sufficient incentives for complete garbage disposal via space launch, this system could help with permanent disposal of highly hazardous nuclear waste. Disposal of nuclear waste via Falcon 9 launch system is estimated to cost only 22.6 to 158.5 times more than existing nuclear waste disposal options, which involve deep underground burial, such as the as the Yucca Mountain repository, which is estimated to cost between $148,000 and $1,041,000 per metric ton of stored heavy metal (MTHM). [9]
© Atticus Cummings. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Beyond an Age of Waste: Turning Rubbish into a Resource," United Nationa Environment Programme, 2024.
[2] C. Pardini and L. Anselmo, "Evaluating the Impact of Space Activities in Low Earth Orbit," Acta Astronaut. 184, 11 (2021).
[3] H. W. Jones, "The Recent Large Reduction in Space Launch Cost," 4th Intl. Conf. on Environmental Systems, Albuquerque, NM, 8 Jul 18.
[4] "Final Environmental Assessment: Falcon 9 and Falcon 9 Heavy Launch Vehicle Programs from Space Launch Complex 4 East at Vandenberg Air Force Base, California," ManTech SRS Technologies, March 2011.
[5] T.-S. Wang, "Thermophysics Characterization of Kerosene Combustion," J. Thermophys. Heat Transf. 15, 140 (2001).
[6] "BP Statistical Review of World Energy," British Petroleum, June 2022.
[7] D. Halliday, R. Resnick, and J. Walker, Fundamentals of Physics (Wiley, 2021).
[8] L. F. Pratson, D. Haerer, and D. Painño-Echeverri, "Fuel Prices, Emission Standards, and Generation Costs for Coal vs Natural Gas Power Plants," Environ. Sci. Technol. 47, 4926 (2013).
[9] "Generic Environmental Impact Statement for Continued Storage of Spent Nuclear Fuel," U.S. Nuclear Regulatory Commission, NUREG-2157, Vol. 1, September 2014.
