This study proposes the novel concept of recycling space debris as a means of supplying material resources for the establishment of a permanent Lunar presence while simultaneously cleaning up Earth’s orbital environment. This expands the scope of traditional debris mitigation efforts, which focus only on removing debris. As a first step, the study presents the creation of a space debris database. A novel classification is made to characterize space debris in terms of material resources and reserves usable for recycling. It is concluded that plentiful defunct upper stages currently drift in Geostationary Transfer Orbits (GTO), presenting substantial risk to other space assets. Their high relative metal content and elliptical orbits make these stages prime candidates for an efficient transfer to the Moon using an Orbital Transfer Vehicle. But as various perturbations have shifted the orbits of upper stages in GTO over the years, the orbital transfer alignment is found to be a critical complexity for a recycling mission. Several mission scenarios are analysed from debris capture to processing on the Lunar surface. The total energy expenditure across the entire mission is used as a novel tool to characterize and compare these scenarios to one another and to the alternative: a direct material delivery mission featuring ESA’s Argonaut lander. By harnessing the unique advantages of electric propulsion, this study shows that the concept of recycling defunct rocket stages is both feasible and viable. A direct, single-target recycling mission shows potential to require 30% lower energy investment per kg of raw material delivered compared to a standard lander mission. A novel thrust-arcing trajectory solves the alignment problem through flexible steering of the apogee to facilitate a Lunar encounter at minimal performance cost. Factoring in the potential to spread launch energy expenditure through a secondary client in a rideshare configuration results in an increase to over 60% less energy investment per kg. A preliminary analysis shows that even greater efficiencies could potentially be achieved through a continuous mission that returns multiple upper stage.
Ultimately, the novel concept of coupling space debris mitigation to advancing long-term Lunar exploration presented in this study shows significant potential and warrants further study. Moreover, a comprehensive analysis of the energy cycle highlights the potential for improved energy efficiency over conventional lander missions. Finally, the use of global energy expenditure as a tool for relative analysis shows potential as an adequate means of analysing space missions featuring distinct segments.

In 1949, Toms (Toms B.A., (1949, 1977)) observed that small amounts of a drag reducing agent (DRA) could cause a considerable drag reduction in turbulent pipe flow. In application of polymer enhanced oil recovery, degradation of polymers in the supply lead could cause clogging. It was, however observed that surfactants at sufficiently high concentration also showed drag reduction without the problem clogging. A DRA reduces the energy loss by friction and unstable flow, thus improving injection throughput with the same pressure pump and thereby reducing the exergetic pumping costs. This study investigates experimentally the drag reducing capacity of surfactants and compares it to the drag reducing capacity of polymers.
For the experiment, a set-up consisting of a pump, a coiled test tube with a length of 1.48 m and an inner diameter of 0.5 mm and pressure gauges is built. The diameter of the coil is 12.5 cm. We use a pump capable of injection up to 200 ml/min. The pressure drop is measured between the entrance and end of the tube. The injection rate is varied between 1 and 200 ml/min, roughly corresponding to Reynolds numbers between 50 and 10,000. The additives are dissolved in brine with a 33,000 ppm salt concentration. The viscosity of the solution is dependent on the concentration of the DRA. The ratio of the measured pressure drop with only brine and the pressure drop with the DRA solution was used to calculate the drag reduction (DR) factor, as from a technical point of view we are only interested whether adding DRA reduces the drag with respect to the original brine solution. From an academic point of view, we remark that for low concentrations the viscosity enhancement due to the presence of the DRA is negligible. As polymers we use xanthan (a biopolymer), and a synthetic emulsion polymer based on polyacrylamide. Maximum DR factors are 23% for xanthan at 90ppm and 32% at 90ppm for the synthetic emulsion polymer. DR only occurs at turbulent conditions.
Three types of surfactants, each from a different branch of surfactants are used in this study. The surfactants used are AOS {훼-Olefin Sulfonate}, CTAB {hexadeCylTrimethylAmmonium Bromide} and APG {Alkyl PolyGlucoside} which are a cationic, anionic and a nonionic surfactant respectively. The surfactants did not show any DR at (for DRA applications) high concentrations up to 20.000ppm. Addition of Sodium Salicylate (NaSaL) to CTAB with a 1:1 ratio led to a maximum DR of 33% at 2500 ppm concentration.
Several pressure gauges have been installed along the test tube in order to observe how the pressure drops along the tube, how the DRAs affect these pressure drops and at what location of the test tube the DR factor is the highest. It is found that xanthan has the same DR factor at each location of the test tube, the emulsion polymer has a decreasing DR factor as the distance from the inlet of the test tube increases and the CTAB+NaSaL DRA has an increasing DR factor as the distance from the inlet increases.
The DRAs are sheared using a constriction in the flow loop while the degradation is monitored. It is observed that xanthan is less susceptible to degradation in comparison to the emulsion polymer due to its more rigid chemical structure. But xanthan and the emulsion polymer would be inefficient to use in looped flow systems as they are affected by degradation. The CTAB+NaSaL DRA on the other hand shows no degradation meaning that the micellar rod-like structures that give the DR effect are being repaired when the shear force is being removed. However, for surfactants higher concentrations (1000-2500 ppm) are required.