A Systems-Level Trade Study of CubeSat Deorbit Strategies Under Mass and Power Constraints: Propulsion, Atmospheric Drag and Solar Activity Effects

The rapid growth of small satellite missions has significantly increased congestion in low Earth orbit (LEO), raising concerns about long-term orbital sustainability and space debris accumulation. CubeSats, due to their low development cost and short mission timelines, are widely used for scientific, educational, and commercial applications. However, many CubeSat missions lack reliable end-of-life disposal mechanisms, leading to an increasing population of inactive spacecraft in LEO. International debris mitigation guidelines therefore emphasize the importance of ensuring timely deorbit of satellites after mission completion. Active deorbiting using onboard propulsion systems provides a controlled and predictable method for orbital decay compared to passive techniques such as atmospheric drag augmentation. Traditional chemical propulsion systems can deliver high thrust but require relatively large amounts of propellant mass, which is a critical limitation for mass- and volume-constrained CubeSat platforms. In contrast, electric propulsion systems offer much higher specific impulse and consequently lower propellant mass requirements, although they operate with lower thrust levels and require longer maneuver durations. In recent years, green propulsion technologies have also emerged as safer and environmentally friendly alternatives to conventional chemical propellants for small spacecraft missions. A first-order analytical treatment of this problem — comparing propellant mass requirements across propulsion types using the Tsiolkovsky rocket equation — provides useful early-stage design insight, but it necessarily neglects two physical effects that matter for a complete picture of CubeSat deorbit behavior: atmospheric drag, which acts continuously on any LEO spacecraft regardless of propulsion state, and the variability of atmospheric density with solar activity, which governs how strong that drag actually is at a given time. Deorbit is rarely a purely propulsion-driven process in practice — drag contributes throughout a spacecraft’s orbital lifetime, and its strength depends on where that lifetime falls within the roughly 11-year solar cycle. This study therefore proceeds in two stages. First, Sections 3.1 and 4.1 present a systems-level analytical trade study of green and electric propulsion for CubeSat deorbit, following theapproach of comparing propellant mass requirements via the Tsiolkovsky rocket equation, and examining how these requirements scale with spacecraft dry mass and available onboard power. Second, Sections 3.2 and 4.2 extend this baseline with a numerical orbit propagation framework — built using scipy.integrate.solve_ivp, with atmospheric density obtained from the NRLMSISE-00 model — that incorporates aerodynamic drag directly into the deorbit model, examines the coupled interaction between low-thrust propulsion and drag, and quantifies how solar activity, via its effect on atmospheric density, changes the rate of orbital decay. This extended methodology was developed in response to detailed technical feedback from Dr. Dario Modenini (University of Bologna, u3S Laboratory). Together, these two stages provide a more complete picture of CubeSat deorbit behavior than either could alone: the analytical stage establishes propellant and power requirements under idealized assumptions, while the numerical stage tests how those requirements interact with two real physical effects — drag and solar-driven atmospheric variability — that are unavoidable in practice.