Asteroids, or more formally, Small Solar System Bodies, offer a wealth of scientific knowledge and, increasingly, economic potential. Regrettably, because of their small size and the fact that the largest groups of asteroids in the solar system are situated tens of millions of kilometers from Earth, ground based observations yield limited data, mostly confined to surface characteristics. To date, space missions traveling to asteroids, or other SSSBs, have also been principally focused upon collecting data from the surface, or within approximately 2m thereof. More penetrative interior survey methods exist in terrestrial application, but methods like seismology and core drilling would require specific equipment and direct landing on the asteroid. Muography potentially presents a means of going in-between these two extremes of the study of asteroid interiors. High energy galactic cosmic ray primaries constantly, and randomly, impact all objects in the solar system, generating secondary showers of particles when they interact with stationary matter. Of primary interest to this project, unsurprisingly, are muons. These particles have a considerable mass, are generally very energetic (>200 MeV), and exist in positive or negative species with a charge magnitude equal to that of 1 electron. These factors contribute to a very low energy loss through conventional mechanisms like ionization,bremsstrahlung, or pair production, making muons very penetrative. Their high energy, highly penetrative nature, and relative abundance as GCR secondaries present an opportunity to perform radiography of the inside of rocks of very large dimensions. Prettyman et al, who have performed initial analyses of the space-bourne tomographic methodology itself, estimate that the interior of asteroids up to 1km in diameter may be surveyed with this technique. This thesis details the project of a feasibility study for a small-scale hodoscopic detector of the type that could be flown with a somewhat standardized satellite bus no larger than the commonly-used ”small” or ”micro” satellite categories for use in just such muography.

CONTEXT. Spectropolarimetry is proposed as a relatively new option in the field of remote sensing for the characterization of aerosol particles and the investigation of cloud properties, that are key factors for the enhancement of climate model's accuracy. The use of multi-wavelength, multi-angle information of the scattered flux and polarization light can lead to the characterization of these particles with unprecedented detail. AIMS. In this context, FlySPEX is a new concept of miniaturized spectropolarimeter that features an innovative system for the polarimetric information encoding in a very limited volume. The aim of this work is to assess an initial estimation of this instrument's accuracy, to create a pipeline for the data reduction of the signal received and to perform a feasibility study in order to adapt this technology to a small satellite mission. METHODS & RESULTS. In order to assess the performance of the instrument a calibration procedure in the optical laboratory has been performed, using 100 % linearly polarized light. A first estimation of the instrument accuracy showed a maximum residual of 0.0056 and a mean residual value of 0.002. A system engineering approach has been developed in order to perform a first study on a space mission concept for the instrument, studying different configurations and analyzing the instrument performance with respect to size, power, pointing accuracy, data rate and resolution of the retrieved data. A 3U CubeSat standard was proposed for the concept of a future space mission and the instrument was adapted to this standard. Twenty viewing points will observe Earth's atmosphere and transmit the signals to a single spectrometer, designed in order to be perfectly compliant with the spacecraft dimensions. Only 1U of the spacecraft is occupied by the payload.

The detection of moons around extrasolar planets is one of the main focuses of current and future observatories. These silent companions contribute to the planets' observed signals but are barely detectable with current methods. Numerous gaseous exoplanets are known to orbit in the habitable zones of stars, and the expected abundance of natural satellites and their diversity in composition make them ideal targets when looking for habitable celestial bodies. Moreover, moons are suspected to play key roles in stabilizing a planet's rotational axis and hence its climate. We show that an exomoon orbiting an Earth-like exoplanet could be identified by measuring the flux and polarization of starlight reflected by the planet-moon system, allowing the characterization of their orbital motions and physical properties.

We have developed, from scratch, a 3D radiative transfer code based on the Monte Carlo method, that fully takes into account the spherical shape of a planetary atmosphere, multiple scattering, and the polarized nature of light. Accounting for the sphericity of an atmosphere is important for the analysis of observations near the planetary limb and the twilight zone, i.e. the regions on a planet where the parent star and/or the observer are low or even below the local horizon. In such regions, the widely used radiative transfer models that are based on the locally plane-parallel atmosphere approximation can lead to significant errors, especially for planets that have extended atmospheres. With our code, we simulate total flux and polarization signals of light that is reflected by spatially resolved and spatially unresolved planets with extended atmospheres. We discuss the effects due to the atmosphere’s sphericity and compare against computations with a locally plane-parallel code. Our results are relevant both for the interpretation of observations of various Solar System planets and moons (with atmospheres) and for the investigation of total flux and polarization signals of exoplanets at all phase angles, including during transits. Especially hot Jupiters are likely to have extended atmospheres and to be detected in edge-on orbits with transits. During a transit, an extended atmosphere can strongly increase the amount of starlight that is measured, thus leading to a smaller derived planet size. We also specifically simulate the polarimetric signal of Titan, Saturn’s largest moon that is known to have an extended atmosphere. We find that at small phase angles, as observed from Earth, Titan’s limb is strongly affected by the sphericity of its atmosphere and that at large phase angles, as observed by a spacecraft like Cassini, Titan’s brightness increases strongly due to forward scattered light.

In the search for understanding the formation and evolution of a solar system, terrestrial planets & any exoplanetary systems, the understanding of the evolution & formation of giant planet's play a crucial role. The primary goal is to study the atmospheres, their physical & chemical processes governed by gases, clouds, and hazes. This research focuses on developing a new technique to characterize aerosol particles using a nephelometer. The new forward model is a two-part model, in the first part, an atmosphere radiative model for Saturn & Venus is developed and the polarization internal field is evaluated using Monte-Carlo technique. The second part of the model is to demonstrate the feasibility of the new instrument technique developed in first part using space system engineering approach. The research concludes that the forward model developed could be used to evaluate the internal polarization field of any planetary atmosphere. The feasibility study of new instrument technique for Saturn’s atmosphere demonstrates a possibility to derive the vertical structure up to 2[bar] pressure & for Venus’s atmosphere in all layers.

During a solar eclipse, sunlight incident on the Earth is reduced due to the (partial) shadow of the Moon. Atmospheric trace gas concentrations which are influenced by the amount of available sunlight, such as nitrogen dioxide (NO2), may be affected due to the disrupted photolysis processes. Large-scale observations of the increased NO2 concentrations caused by the solar eclipse would improve our understanding of the sensitivity of NO2 in the atmosphere to short-term variations in sunlight. Spaceborne measurements can provide valuable information about the large-scale spatial distribution of NO2, which is provided daily by the TROPOMI instrument aboard the Sentinel-5 Precursor satellite by measuring and retrieving locally reflected sunlight. However, the TROPOMI NO2 retrieval is unable to derive reliable concentrations during a solar eclipse, as solar eclipses are not taken into account in its retrieval algorithm. In this research, we have adjusted the NO2 retrieval of TROPOMI such that it can handle solar eclipses and study the large-scale response of NO2 during two solar eclipses over Europe in 2021 and 2022. We found a large-scale increase of NO2 in the adjusted measurements, which linearly correlated with the degree of obscuration. We compared the measured NO2 increase with the values from the atmospheric chemistry model TM5 including an applied eclipse implementation and we found a close agreement in most areas that are not highly polluted. Our measurements and model predict a NO2 increase of 60%±12% and 70%±7% for an obscuration fraction of 1, respectively. More advanced chemistry modelling work is needed to explain the measurements in highly populated areas. We conclude that our results demonstrate that the TROPOMI algorithm is capable of correctly measuring NO2 after an adjustment of the NO2 retrieval. We have shown that it is possible to adjust an atmospheric trace gas retrieval for the influence of a solar eclipse. Moreover, we are the first to provide evidence for an increase in NO2 during a solar eclipse using space-based measurement techniques and to quantify this increase on a large scale with the same instrument. Our measurements can be used to test atmospheric chemistry models, possibly improving their sensitivity to solar eclipses but also artificial shadows on the Earth induced by sunlight-intercepting geoengineering approaches.

Human exploration on Mars is nearing actualisation and the space industry is therefore in need of vehicles with the capability of transporting goods and exploring the surrounding area. Current Mars rovers by NASA, such as the Curiosity, provide excellent researching capabilities from a remote location. However, these land based drones are slower and less manoeuvrable around obstacles than airborne vehicles would be. Due to the need of transportation and exploration, this report aims to get acquainted with current research on Mars flight and provide a preliminary design concept enforced by the following mission goal: ”To aid future Mars colonists by providing a feasibility study of a flying vehicle capable of carrying a predetermined payload.” To approach this goal, it was decided to determine which flying vehicle concept would be the most optimal in a Martian atmosphere via a trade-off analysis. Four options were considered and a balloon was deemed more optimal for a Martian environment compared to aircraft, rotor craft and flapping wing vehicles. The main reasons for this are that the balloon is the most power efficient and is a design that provides the least amount of risk concerning likelihood of failure and safety of astronauts.Thereafter, the process required to design a hot air balloon and the programming of the code is described. Results indicate that a balloon with a prolate ellipsoid shape is optimal with the ratio between the minor and major axis being 0.41, therefore resulting in a balloon with a major axis radius of 33.8 푚 and a minor axis radius of 13.86 푚. A surface area of 131.58푚² is selected for the flexible solar cells which have been calculated to be able to power a two propeller system ensuring that the balloon can counter headwinds of up to 15푚/푠. Finally, to ensure altitude control is possible, a venting system is applied on the top of the balloon ensuring a venting volume of 117푚³ is possible. This is enough to ensure the balloon can land, take-off and control its altitude as desired.This thesis is therefore able to provide an initial design for a Mars exploration balloon capable of controlling not only its altitude but also its position. This is achieved by using the solar energy to increase the balloon’s temperature and a vent area of 19.03 푚² to control this temperature. All this provides a design that can be controlled and meets the versatility requirement as it is capable of carrying a variety of heavy payloads and fly past ground obstacles

Uranus is one of the most intriguing and unexplored bodies of the Solar System. Its mysteries include its active atmospheric dynamics, its low internal energy, its extreme obliquity, its complex magnetic field, and its ring and satellite system containing possible ocean worlds. As of today, none of the current formation and evolution models can explain all its chemical and dynamical aspects. An in-situ mission to study Uranus' atmosphere could provide answers to this planet's mysteries, enabling the measurement of its deeper layers. A 6 DoF flight simulator was designed, with a focus on identifying the specifications and limitations of its Guidance, Navigation, and Control modules, for feasibly flying in Uranus' challenging atmosphere, and providing new science return. The mission architecture consists of two gliders flying near the planet’s equator and north pole until the 100 bar pressure level for around 13 Earth days, supported by an orbiting spacecraft in a circular, equatorial, and synchronous orbit, for continuous trajectory tracking and relay of the scientific data to Earth ground stations. Due to Uranus’ opaque atmosphere, typical optical navigation sensors such as star sensors, Sun sensors, and imagers are avoided. Instead, the modelled navigation sensors are taken from the payload suite.

When sunlight illuminates a body, a tiny pressure is exerted upon its surface due to the photons impacting on it. Such a principle forms the basis of solar sailing, in which the solar radiation pressure is used to accelerate highly reflective lightweight structures called solar sails. Similarly, a laser-enhanced solar sail is a solar sail in which also an external laser beam pointed towards the sail is exploited to generate thrust. In this way an additional laser radiation pressure is exerted onto the sail, hence conferring higher propulsive and steering capabilities, and leading to an increased maneuverability of the sailcraft. The main purpose of this thesis project is to provide a model of the laser-enhanced solar sail dynamics and to establish the advantages of laser-enhanced solar sailing as compared to "traditional" solar sailing. The analysis has been pursued focusing on interplanetary missions and considering ideal sails, i.e. sails able to perfectly reflect the impinging radiation. Normally, for low-thrust interplanetary missions the propellant consumption and time of flight required for the transfers to take place play a crucial role. However, since solar sails do not exploit any propellant, the traditional and laser-enhanced sailcraft performances have been compared by analyzing their flight-time optimal trajectories, focusing on three different mission scenarios: a Mercury orbit rendezvous, Mars orbit rendezvous and Neptune flyby. These trajectories have been computed by taking advantage of an evolutionary neurocontrol optimizer, in which newly added functionalities have been implemented with the purpose of optimizing laser-enhanced solar sail trajectories. The trajectory analysis results have shown that, if laser-enhanced sailcraft are used instead of traditional sailcraft, flight time gains in the order of 8-11% can be achieved for the missions to Mercury and Mars orbits, while a smaller 2.5% gain is achieved for the flyby mission to Neptune.

Aims: Analysing historical disk-integrated polarization data of Venus with the help of numerical simulations to learn about the time variability in cloud and haze properties, the position of the UV-absorber and the polar cap regions. Method: With numerical simulations, polarization curves will be calculated for specific input conditions. We compare numerically computed polarization curves to the historical polarization data to derive the microphysical properties of Venus's cloud and haze particles. Results: From our research we obtain values for the imaginary part of the refractive index of the cloud particles of the order 10^(-4). It is most likely that the absorber is mainly located at the equator or in patchy clouds covering 80% of the planet. It is found that in the presence of precise disk-integrated polarization data, it is possible to detect variations in the polar regions. For Venus we found that it is likely that there exist larger particles at higher altitudes at the Venus poles. Unfortunately, it is very hard to say something about the long term variations on the planet. For the Venus case, it can be roughly stated that: the polarization was higher in 1975/1976 than in 1965/1968; the polarization was also higher in 1968/1970 than 1965/1968 but not higher than in 1976; there was a decrease in the polarization of the ultraviolet region in the years 1964/1965. Conclusions: Future observations should be made in a broad range of wavelengths, at as many phase angles as possible and in time frames similar to the orbital period of the (exo)planet. Since Venus can be observed as if it were an exoplanet (broad range of observable phase angles and disk-integrated data), we applied this research to exoplanets as well. We concluded with the help of the Venus data and simple models that it is possible to obtain cloud properties, such as the refractive index and the optical thickness of the cloud, of exoplanets using polarization observations. It was found that those properties are harder to distinguish using flux measurements since the geometric albedo and the distance to the planet are unknown.

Due to the insufficient worldwide efforts to reduce greenhouse gas emissions and related global warming, marine cloud brightening (MCB) is gaining interest as an instrument to artificially lower Earth's temperature. MCB is based on exploiting the aerosol-cloud effects to enhance the albedo of stratocumulus clouds and prolong their lifetime by injecting clouds with sea salt aerosols. As there are still many uncertainties in the expected output of MCB due to the unresolved questions related to cloud processes and feedback mechanisms, this thesis aims to assess the efficacy of MCB to enhance solar radiation reflection of stratocumulus clouds using the turbulence-resolving Dutch Atmospheric Large-Eddy Simulation model. This assessment is made by investigating which cloud properties and processes that determine the cloud's radiative forcing are affected by the aerosol injection for different meteorological conditions and injection strategies in 30-hour simulations. The simulation domain has a horizontal size of 25.2 $ imes$ 25.2 km$^2$ and 2 km in the vertical, with a mesh size of 100 m horizontally and 20 m vertically. The two studied cloud cases are based on the measurements of the first and second research flights of the DYCOMS-II field experiment and are characteristic for a shallow stratocumulus-topped boundary layer (STBL). The investigated surface aerosol injection strategies are a horizontally uniform source and a point source that is restricted to a single grid cell. In addition, an assessment is made of the effects of differences in aerosol number concentrations between the STBL and the free troposphere on the cloud's aerosol number concentration and radiative properties. This is done in 6-hour simulations with and without a uniform aerosol source, based on the second research flight of DYCOMS-II. The simulated horizontal domain is 3.2 $ imes$ 3.2 km$^2$ and 2 km in the vertical, with a mesh size of 25 m horizontally and 20 m vertically. Our simulations showed that boundary layers with relatively low background aerosol concentrations were most effective in generating a negative radiative forcing, compensating slightly less than half of the forcing related to the CO$_2$ doubling in the atmosphere. For boundary layers with an average background aerosol concentration, the radiative forcing approaches a quarter of this value, which diminishes to negligible effects for boundary layers with relatively high background aerosol concentrations. For precipitating boundary layers, the enhanced radiative forcing is mainly caused by its suppressing effect on precipitation. For non-precipitating boundary layers, the reduction in cloud droplet size showed to be the primary source of the enhancement. No pronounced differences in efficacy were found when using a homogeneously distributed aerosol source or a point source. For the two studied cloud cases, investigation of the contributions to changes in the liquid water path showed that to exploit the effect of aerosol injection on the liquid water path, it is most effective to suppress precipitation and enhance cloud cover. The differences in aerosol number concentration between the STBL and the free troposphere significantly and consistently altered the aerosol number concentration in the cloud layer due to the entrainment of air from just above the cloud-top into the cloud layer. This indicates that these differences in aerosol number concentration need to be considered when modelling MCB, as they change the intended aerosol number concentration enhancement and thereby affect their cloud-modifying effects.

Asteroid Reflection Model (ARM) is a newly developed model that simulates reflected radiation and polarization on an asteroid's surface. The working principle behind the model is radiative transfer using Fourier series expansions of reflection matrices. Input models and parameters are: a triangle polyhedron shape model of an asteroid, a surface scattering model, and the desired asteroid location and orientation and the phase angle. Output parameters are the reflected Stokes vector and the degree and direction of polarization, for each individual surface facet and disk-integrated. ARM is fully verified. Generated phase-polarization curves are validated using polarimetric data of four asteroids, including (3200) Phaethon, for which various surface scattering models are deployed. These phase-polarization curves are fit to the Phaethon data, but this did not result in a good match for any of the surface scattering models, since they fail to simulate the opposition effect. However, the effect of the shape, orientation and the rotational motion is clearly visible in the results, as is the relation between wavelength and polarization. Finally, it was concluded that the polarization is favored over the flux when determining an asteroid's surface characteristics and shape, and that both flux and polarization can be used together when determining its size.

This thesis studies the radiation dose deposited on a 6U CubeSat in interplanetary orbit. The European Space Agency’s radiation data tool SPENVIS has been used to determine the proton flux in interplanetary space during a solar particle event which occurs only once every one hundred years. SPENVIS has further been applied to obtain a dose depth curve for this specific 1-in-100 years proton flux. Simultaneously, 6U simplified models of several materials are created as well as a realistic 6U CubeSat structure which represents the state-of-the-art in CubeSat industry. Using radiation simulation tool Fastrad, two simulations have been performed: ray-tracing simulation and forward Monte Carlo simulation. Ray-tracing simulation provides a sector shielding analysis of the models, giving an overview of the received radiation dose for each specific point in the models. Forward Monte Carlo gives an overview of the deposited radiation for each part of the model, which has shown especially beneficial for the state-of-the-art model, in which deposited dose has been obtained for each part in the model. This has led to a dataset that shows the radiation dose deposited at each location and in each part of the 6U CubeSat structure during a 1-in-100 years solar particle event that strikes in interplanetary space.