Analysis of innovative scenarios and key technologies to perform active debris removal with satellite modules
Year: 2015
Type: article
Abstract: It has surely happened sometimes to look at the night sky and catch sight of a small, brighting spot moving like an airplane, but without ashing as usually airplane lights do: it was a satellite. It is always amazing to think that there are objects that continously orbit around Earth, so far from us. Maybe, it is not well-known that they are a lot...thousands...more or less 17,000 those closer to the Earth, to be precise. It is difficult to imagine how so much objects can orbit without touching or colliding each other. From the beginning of the space activities in 1957, an enormous number of objects have been sent or released in space, and thinking that space is so limitless that it could contain everything, all these objects have been abandoned in orbit. The result has been the creation of a great quantity of debris that have began to represent a serious threat for future space missions. Recent studies revealed that if no countermeasures are going to be adopted to reduce the generation of debris in orbit, like for example spent spacecraft and orbital stages, the space population could remain stable only for the next 20 - 30 years. Beyond that, collisional cascade events between objects already in orbit will cause a rapidly increase of debris, even in case of a complete hault of launches. This self-sustained phenomenon, known as Kessler Syndrome, would prevent any other human access to space. Although from '90s, mitigation measures have been proposed to limit the generation of debris in orbit, they appeared to be insufficient to guarantee a long term stability of the space environment. The only way to intervene would be the implementation, in parallel, of active debris removal (ADR) missions. The effectiveness of such kind of missions has been demonstrated, but there are numerous aspects that have to be solved yet in order to make them feasible in the near future. On one hand new mission studies and analyses are required to identify the most efficient ADR scenarios. On the other hand, there are several technological issues that are particuarly critical, espacially as regards the capture of space debris, that are essentially un-cooperative objects and so, not-specially-prepared to be grasped. The research developed in this thesis deals with two of the main aspects related to active debris removal: I) ADR mission analysis, II) developement of an enabling technology for ADR; in the specific case, the development of a morphing adhesive interface to capture uncooperative ojects. A multiple vehicles scenario, where orbital transfers and de-orbiting operations are accomplished by distinct vehicles (a space tug for the former, proper de-orbiting kits for the latter), is selected for the analysis. The innovative solution proposed is the employemnt of modular structures as de-orbiting kits, constructed by assembling a certain number of microsatellite elementary units, equipped with proper de-orbiting devices; the number of assembled units depends on the characteristics of the debris, in terms of mass and initial orbit, as well as to the specic de-orbiting technology selected. An increased mission efficiency, reliablity and exibility are expected from the adoption of such approach. Costs and mass savings can be also expected, as well as economy of scale, thanks to the standarization of the units employed. Four de-orbiting solutions are implemented in the analysis: drag sails, electric propulsion, electrodynamic tethers, hybrid propulsion. Different mission scenarios are analysed, to determine the performances of each solution, in terms of de-orbiting kit mass and total de-orbiting time. For each de-orbiting technlogy, a proper base unit is determined. An optimization procedure to perform multiple orbital transfers and, hence, minimize the mass of the propulsion system of the space tug, is also performed. Five orbital bands are identified as priority regions, where debris have mass between 800 kg and 11 tons and orbits between 800 km and 1000 km. The analyses revealed that, although drag sails are low-cost and simple solutions, they are not suitable to de-orbit massive debris from high altitudes since very large sails could be required, with consequent high risk of collisions during the de-orbiting phase. Electric propulsion and electrodynamic tethers are both promising solutions for ADR: for debris with mass 2000 kg they are comparable, both in terms of de-orbiting kit mass and total de-orbiting time. For more massive debris, mass 2000 kg, electrodynamic tethers performes better from the remover mass point of view, but higher de-orbiting time is required compared to electric propulsion. Risks assessment evaluation revealed that in this case the probability for the electrodynamic tethers to be damaged in consequence of collisional events with debris up to 10 cm exceeded the limit of 0.001 indicated in the NASA-STD-8719.14. The risk analyses conducted for electric propulsion, on the other hand, did not reveal any risk of catastrophic collision during the deorbiting manoeuvre. Hybrid propulsion resulted the most massive solution among those implemented, but it represents the fastest solution in terms of de-orbiting time. The second part of the research activity is focused on the development of a morphing adhesive interface to be integrated as end effect of a robotic mechanisms to allow the capture of uncooperative objects. Two technologies are investigated in the realization of the interface: shape memory polymers, for the morphing behaviour, and electroadhesion for the adhesion capabilities. Two prototypes are then developed and tested. It is observed that mechanical pre-load as well as electrostatic force increase the normal adhesion performances of the realised interface. Normal adhesion pressures can vary between 0.55 and 1.4 kPa without the contribution of electrostatic forces, as the mechanical pre-load is varied between 1.5 N and 10 N. The adhesion pressure increases in presence of electrostatic forces, varying between 1.40 kPa and 1.80 kPa for different mechanical pre-load and voltage conditions. The forces achievable range between 3.5 N and 11.5 N. Morphing tests are also performed to verify the morphing-adhesive capabilities of the developed interface. The tests demonstrates taht the presence of a foam substrate could be advantageous as regards the capture of uncooperative objects, allowing a good compliance between two contact surfaces even in presence of macroscopical irregularities, enhancing the adhesion between them. The effectivness of the proposed morphing-adhesive interface is then demonstrated.
Author: Livia Savioli
Language: English
Subfield: Aerospace Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2292791650