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The Earth Space Elevator is an ingenious concept aimed at providing easy access to space, eliminating the need for rockets and potentially reducing drastically the launch costs. Technical advancements that could make the Space Elevator possible, among others, would be the availability of long carbon nanotubes or other super-strong and light material. This paper aims at addressing issues related with the stability of the system when the elevator is partially deployed starting from a nucleus in geostationary orbit (GEO). As noted by various authors, the energy increase needed to keep the orbital centre (where the gravity and centrifugal forces balance out) at GEO altitude during deployment while the tether is lengthened leads to an orbit with a positive orbital energy, i.e., the circular orbit has an energy level pertaining to a hyperbolic orbit. This situation leads to the instability of the unanchored system that would tend to escape from the geostationary orbit. The paper illustrates the change in orbital energy during assembly for a system made of a cylindrical tether and then investigate the stability of the coupled orbital and attitude motion in the orbital plane before anchoring. The analysis leads to the conclusion that the orbital motion instability ensues well before the orbital energy of the unperturbed system becomes positive.

This paper presents the concept of a dual cubesat mission designed for Moon exploration that enables scientific measurements that are not accessible by high orbital or landed missions thanks to the use of a long passive tether for orbital insertion. Due to the intrinsic characteristic of the Moon environment, low altitude orbiting spacecrafts are in fact requested for mapping key parameters such as plasma, volatiles and magnetic field. Inserting a satellite in such low trajectories from an orbiter has usually a high cost of propellant to achieve the orbit change or requires a long time to finalize the maneuver with electrical propulsive systems. Limitations are even higher for cubesats that have very limited capacity for orbital adjustment, so they cannot perform substantial orbital changes by using classical propulsive techniques. The use of a long passive tether to exchange momentum between two cubesats can eliminate such drawbacks and provide fast, far-reaching and accurate orbital changes with almost no propellant being consumed. A mission scenario is presented with the two mated cubesats released by an orbiter in circular Moon orbit at 500 km altitude. Thanks to the momentum exchanges provided by the swinging tether the upper cubesat will be left in a 520 × 737 km orbit and the lower cubesat into a 460 × 26 km orbit with a low periselenium that provides an ideal altitude for close observation of the lunar surface and monitoring of characteristic parameters of the Moon environment. With a high-inclination orbit, the low-altitude orbital passes will map the entire Moon surface in around 14 days. The upper cubesat will be transferred on a highly predictable and low-perturbation orbit and equipped with laser corner reflectors and a radio link band transponder to allow tracking both from laser stations on Earth (Matera, Italy ASI geodesy station) and from the Lunar Orbiter via radio link. The integrated analysis with radio signals between Cubesats can also be used to improve orbit determination and study perturbation effects on orbital dynamics.