This study evaluates the feasibility of reusing lightweight solar sails in order to transport 1.69 * 10^6 sunshades, made out of occulting membranes with free-standing SiO2 nanotube films, to the adjusted sun-Earth Lagrange point, L1'. The purpose of the study was therefore to evaluate if this method is sufficient enough to lower Earth's average surface temperature by 1 degree C within a reasonable time frame, due to the rapid climate change, and compare the total launch mass to previously proposed methods. Two mission times of 10 years and 15 years were used, and three different starting altitudes, the GEO, MEO and LEO orbits, were investigated. The results showed that the method in this study was feasible for all combinations of starting altitudes and mission times. The solution where the mission time was set to 15 years and where the starting altitude was set to the GEO orbit, resulted in a launch mass of 11\% of the mass of the previously proposed solution. Furthermore, the investigation showed that high altitude starting orbits and long mission times resulted in a lower launch mass. However, in order to fulfill the goal of reducing the average temperature by 1 degree C in a reasonable time frame, the mission time cannot be too long. Finally, the results and calculations in this study are partially based on assumptions and simplifications, and therefore the results should be considered as approximations and not exact analytical solutions.

To mitigate climate change a proposed space-based geoengineering solutionis to screen off solar irradiance by placing a membrane in between the Earthand the Sun. The feasibility of such a project largely depends on minimizingthe mass of the shading screen and as an extension to the Sunshade projectthis thesis investigated how such a low-mass membrane could be designed.Because of the acting forces at location in space, minimizing the mass impliesthat the material ought to have a low reflection coefficient and surface densityand therefore the highly transparent material of artificial spider silk was chosenas the proposed material. The only possibility to block light is then byrefraction or diffraction and, since the presence of apertures might lower thesurface density, the structure of the suggested membrane is a grid patternof wires. Such a diffraction grating was investigated while applying twomethods. Method 1 optimized the dimensions of the structure to lower thetotal transmission on Earth when placed on the direct transmission axis ofthe membrane and method 2 tilted the membrane in order to place Earth ata diffraction minimum. This resulted in three suggested designs A, B, andC with surface densities varying from that of 0.00867 to 0.228 gm−2. Theresults were compared with two previous design proposals where the lowestareal density was 0.34g/m2, which is 3/2 to 40 times larger than the densitiesproposed in this paper. The reflectivities for A and B were 12.5 and 3.75 timeslarger than that of the smallest previously achieved reflectivity. The reflectivityof C could not be determined exactly but ought to have a reflectivity at leastas low as B at 3%, making it the most promising candidate for a membranedesign of the three.

The purpose of the study is to evaluate the possibility of using gridded ion thrusters as a means of attitude control for a solar sail as a part of the sunshade project, which aims to place 10^8 solar sail sunshade spacecraft, each with an area of about 10 000 m^2, at the Sun-Earth Lagrangian point L1 in order to reduce Earth's global temperature. Two types of solar sail sunshade spacecraft were studied. The first type, referred to as the sunshade demonstrator, had an area of 100 m^2 and a mass of 10 kg, and the second type, referred to as the full-sized sunshade, had an area of 10 000 m^2 and a mass of 90 kg. To determine the significance of using ion thrusters for the attitude control system, the mass of the required fuel, as well as the total mass that had to be added to the spacecraft to implement the attitude control system, was calculated. Two types of journeys were studied for each spacecraft type: starting from Low Earth Orbit (LEO) to L1 and from Geostationary Orbit (GEO) to L1, respectively. The results showed that the duration of the journey of the full-sized spacecraft was about 570 days from LEO to L1 and 370 from GEO to L1, respectively. The required amounts of fuel for the respective journeys were 580 g and 15 g, respectively, and resulted in a total additional mass of 7.8 kg and 7.2 kg, respectively.