Design and Analysis of a Passive Tether De-Orbiting Mechanism for a Nano-Satellite

This paper aims to characterize the forces acted upon a 2U-class Nano-satellite by a passive electrodynamic tether system used as an inexpensive, space and mass efficient de-orbiting mechanism in the Low Earth Orbit (LEO). As stated by the IADC guidelines, an object in the low earth orbit should not have an orbital lifetime exceeding 25 years which can be attained by the satellites themselves due to significant atmospheric drag. The de-orbiting system involves a spool with an electrically conducting thread wound around it. It is ejected using a spring-loaded mechanism with the other end of the thread secured to the satellite body. The shape of the spool and the type of winding have been optimized to ensure maximum packing efficiency and a stable ejection. It has resulted in a tether length of around 300 meters for the considered system. The mass of the spool with the tether winded upon it is about 80 grams (mass of the tether being 32 grams) which makes it a suitable solution for small satellites with stringent mass constraints. Study of the forces acting on the satellite body during the deployment becomes essential to avoid the destabilization of the satellite which would result in the winding of the tether about the satellite body. Excessive tension on the tether during the deployment phase might result in a failure of the thread material. The forces acting on the system during the deployment phase have been analyzed. Methods to reduce and dampen these destructive effects have been discussed in detail. Once deployed, various forces act on the satellite system due to the interaction of the conductive thread with the time-varying magnetic field and the ambient plasma. Being a passive tether system, it experiences a change in the direction of the magnetic field while crossing over the poles resulting in the force to be applied in the same direction in different parts of the orbit. This force, always opposing the motion of the satellite, increases the eccentricity of the satellite orbit causing it to burn up at the perigee in under 2 years as opposed to 25 years. A detailed study on the respective forces and its effects on the satellite's orbit has been carried out in this paper.