The main topic of this thesis concerns itself with the development and analysis of optical components used in CMB (Cosmic Microwave Background) missions in the terahertz frequency spectrum. In particular, the optical performance of PRISTINE, a mission proposal for the ESA fast (F) mission call and a PLA (Polylatic Acid) GRIN (Gradient Index) lens was analysed using GBM (Gaussian Beam Mode) theory and PO (Physical Optics). This thesis also includes the work the author did as part of an international team of 16 students to design a candidate ESA mission. The final chapter, therefore, concerns itself with “Geophysics from Space using Micro-or Nano-Satellite Constellations” and is separate from the rest of the thesis. Detailed analysis of PRISTINE was carried out in GRASP 10.5 a commercial package which uses PTD (Physical Theory of Diffraction ) and PO to measure the EM (Electromagnetic ) radiation generated from reflector antennas. The EM fields predicted from GRASP were compared with GBMA (Gaussian Beam Mode Analysis). The beam quality of PRISTINE was tested using its Gaussicity and ellipticity (this was the chosen method used to compare the simulated data with the theoretically predicted data). Each surface of PRISITNE’s twelve mirror pFTS (polarising Fourier Transform Spectrometer) was designed using code written by the author to optimise the focusing and collimation of each elliptical surface from criteria outlined in Chapter 3. Chapter 4 deals with the design, manufacturing and analysis of a 3-D printed PLA GRIN lens designed to focus W-band radiation (75-110 GHz) 250 mm from the lens. For this, a commercial package known as CST microwave was used to analyse the refracted radiation. The simulated radiation was also compared with GBM analysis and the experimental lab data performed in Maynooth University’s VNA (Vector Network Analyser) laboratory. Along with this, some material analysis was performed at 100 GHz in the laboratory to determine the permittivity of the PLA. The final section of this thesis moves away from quasi-optical analysis and instead concerns itself with Geophysics. MAGMA-C is a proposed eight satellite constellation in a Low Earth Orbit (LEO) to measure the Earth’s magnetic field to study the induced magnetic field in the mantle. The primary goal of the MAGMA�C mission is to map Earth’s mantle conductivity derived from its induced magnetic field. The secondary goal of this mission is to use this conductivity profile to better estimate the water content of the mantle.