Preliminary Sizing and Structural Design of a Drag Sail Deorbiting System for CubeSats in Low Earth Orbit

Abstract

The growing accumulation of space debris poses a significant threat to the long-term sustainability of space activities. A drag sail system presents a passive, post-mission disposal solution that utilizes the low atmospheric density in Low Earth Orbit to accelerate the re-entry and disintegration of satellites. This study focuses on the sizing and structural design of a drag sail system based on a preliminary design provided by Demcon High-tech Systems.

A numerical orbital decay model was developed in Python using Tudat libraries to determine the drag sail area that complies with the decay time requirement. The conservative perturbing forces, such as the Earth’s gravitational field (including oblateness effects) and third-body gravitational influences, as well as non-conservative perturbing forces, such as atmospheric drag and solar radiation pressure, were
included. The atmospheric density was estimated using the US76 neutral model and the NRLMSISE-00 dynamic model, with the latter yielding a more accurate result. Furthermore, two aerodynamic flow models: free molecular and continuum flow, were analyzed, showing a minor 4% difference in decay time. The results reveal that an accurate representation of atmospheric density is more critical than the drag coefficient due to the high variability in density predictions between models. Through validation of the model, it was found that using the average outer surface area of the CubeSat as the effective drag area offers a conservative yet reliable estimate for decay prediction.

The natural decay time of the host spacecraft was estimated at 31.4 years. The drag sail was designed to reduce this to 6.3 years, meeting the mission’s fivefold reduction target. Analysis of the area-to-mass ratio indicated a ratio of 54 cm²/kg, corresponding to a drag sail area of 0.2 m², will comply with the decay requirement time.

For the structural design of the booms, inflatable deployable structures were selected due to their compactness and long shelf-life, with strain rigidization as the post-deployment stiffening technique. Localized low rigidization near the boom end caps was observed. The sail configuration limited out-of-plane deflection to 2 mm, ensuring no effective drag area reduction or decay time increase. Stresses on the sail were well below failure thresholds, and its lowest natural frequency was 200 times greater than the highest frequency of the drag load, eliminating resonance risk.

Boom analysis revealed that bending is the primary failure mode. Lower inflation pressures enhanced bending performance, with the lowest pressure studied allowing the boom to withstand over five times the applied drag load before yielding. This significant safety margin accommodates potential imperfections, such as residual creases remaining after rigidization. Additionally, vibrational coupling between
the sail and booms was avoided, thanks to a sufficient frequency separation of four times between the subsystems.

A final full system analysis indicated the deorbit system could survive the mechanical stresses induced by the drag load down to an altitude of 120 km. However, further investigation is needed to account for thermal loading at lower altitudes.