Thesis (doctoral)--Friedrich-Wilhelms-Universität Berlin, 1869. / Vita.

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Impact-induced seismic vibrations have long been suspected of being an important surface modification process on small satellites and asteroids. In this study, I use a series of linked seismic and geomorphic models to investigate the process in detail. I begin by developing a basic theory for the propagation of seismic energy in a highly fractured asteroid, and I use this theory to model the global vibrations experienced on the surface of an asteroid following an impact. These synthetic seismograms are then applied to a model of regolith resting on a slope, and the resulting downslope motion is computed for a full range of impactor sizes. Next, this computed downslope regolith flow is used in a morphological model of impact crater degradation and erasure, showing how topographic erosion accumulates as a function of time and the number of impacts. Finally, these results are applied in a stochastic cratering model for the surface of an Eros-like body (same volume and surface area as the asteroid), with craters formed by impacts and then erased by the effects of superposing craters, ejecta coverage, and seismic shakedown. This simulation shows good agreement with the observed 433 Eros cratering record at a Main Belt exposure age of $400 \pm 200$ Myr, including the observed paucity of small craters. The lowered equilibrium numbers (loss rate = production rate) for craters less than $\sim 100$ m in diameter is a direct result of seismic erasure, which requires less than a meter of mobilized regolith to reproduce the NEAR observations.This study also points to an upper limit on asteroid size for experiencing global, surface-modifying, seismic effects from individual impacts of about 70-100 km (depending upon asteroid seismic properties). Larger asteroids will experience only local seismic effects from individual impacts.In addition to the study of global seismic effects on asteroids, a chapter is also included which details the impact ejecta plume modeling I have done for the Deep Impact mission to the comet Tempel I. This work will also have direct application to impacts on asteroids, and will be used in the future to refine the cratering history modeling performed thus far.

The amount of interest in asteroids, particularly near-Earth asteroids, has been slowly increasing the last few years. Early on, it was the fear of the potential hazards of an asteroid impact (which still remains); now, science and exploration are driving the motivation for detecting asteroids. By incorporating a process that attempts to remove stars from images, known as difference image analysis, into the shift and stack method for finding moving objects, an algorithm that searches for asteroids in series of images was created. When tested on previously discovered asteroids, the algorithm was able to detect 73% (104 out of 142) of the asteroids, with a false positive occurring in roughly one in six runs. Two of the test asteroids found by the algorithm were not found using a different shift and stack technique. Almost all of the asteroids that the algorithm could not detect were either slow moving, faint or both. The detection capability of the algorithm can easily be improved to be more successful at detecting slow and/or faint asteroids. This can be achieved by using a better method for masking the star residuals or by increasing the time between successive images when searching for asteroids with velocities of 2.4

Thesis (M.A.)--Lehigh University, 1910. / Current name of asteroid is "691 Lehigh." Manuscript. Also available online.

Cette thèse étudie la problématique d'un atterrissage sur un astéroïde. Le lander est un paquet scientifique dépourvu de plateforme de navigation. Il est placé dans une région dont la dynamique est favorable à l'atterrissage. Une étude de l'interaction entre le lander et la surface permet de comprendre quels critères physiques du lander affectent son atterrissage. / This dissertation investigates landings on an asteroid. The lander is a scientific package devoid of any navigation platform. It is released in a region dynamically favorable to landing. The study of the interaction between the lander and the surface shows the possible trade-offs on the lander physical properties that may affect its landing.

This thesis is a feasibility study for a crewed mission to a Near Earth Asteroid (NEA). An alternate dual-launch architecture is proposed and analyzed against a more established architecture. Instead of a rendezvous in a low-Earth parking orbit, the new architecture performs the rendezvous while the two spacecraft are on an Earth-escape trajectory to the destination NEA. After selecting a target asteroid, 2000 SG344, each architecture will have its best mission compared to the best mission of the other architecture. Using the new architecture, a mission is created to the chosen NEA, 2000 SG344. A back-up Orion MPCV and a Habitation Module are launched first on a cargo configuration SLS. A crew of two astronauts is launched two hours later in the primary Orion MPCV by a crewed configuration SLS. Both of these launches are on an Earth-escape trajectory and begin rendezvous after two full days in outer space. The completed spacecraft journeys the rest of the trip to the NEA. For a period of eight days, the spacecraft remains in a tight control sphere near the asteroid by using a control algorithm and the rendezvous thrusters. The astronauts have this period to perform their EVAs and accomplish their mission objectives at the NEA. The spacecraft then departs the NEA and returns to Earth. The entire mission is 134 days and requires 2.054 km/s of Delta-v maneuvers to complete. An analysis of multiple Lambert's methods is also done due to their extensive use in this thesis. Many of the most popular Lambert algorithms are compared by evaluating each on its accuracy, speed, and singularities. The best Lambert method to use for the orbital analysis in this paper is Battin's method because it is accurate, quick, and robust for all cases that will be observed.

Asteroid mining is rapidly becoming a popular topic amongst space community, primarily due to the potential resources that the asteroids can provide for future spacefaring. One of the interesting resources that can be obtained from asteroids is water, which can also be processed into oxygen and fuel. An intriguing concept would be to process fuel from asteroid, and establish a fuel depot in an Earth-centered orbit. This thesis considers a mission concept consisting of travelling to an Arjuna near-Earth asteroid from a lunar distant retrograde orbit as a depot orbit, processing fuel in-situ from the water on the asteroid, and bringing back 100 tons of fuel to the depot orbit. In order to minimize fuel consumption for such a trip, the thesis develops an optimization method that can obtain the best trajectory for different phases of the round trip, given certain constraints to ensure the spacecraft successfully reaches the asteroid and comes back to the Earth system. The optimization model consists of four steps, i.e., the outbound trip, the first phase of the return trip, the second phase of the return trip, and the optimization for the combined phases of return trip. The outbound trip is the trajectory from the depot orbit to the asteroid. After at least three months of mining, the spacecraft brings back the processed fuel to the vicinity of the Moon. This phase is called the first phase of the return trip. The spacecraft is then captured without an insertion burn to an Earth-centered orbit by a lunar gravity assist maneuver, and travels to the point where the insertion maneuver to the depot orbit begins. This is the second phase of the return trip. The last step of the optimization is the combination of the two phases of return trip, in addition to the final maneuver for entering the lunar distant retrograde orbit. The optimization method uses MATLAB fmincon solver, and it was applied to 29 synthetic asteroids. There were 19 converged solutions, but for 10 asteroids the optimizations was not able to converge. The lowest minimum fuel consumption for a trip is 19965.5 kg, and the highest minimum fuel consumption is 61821.4 kg. For the lowest minimum fuel consumption, the duration of the trip is nearly 7 years, and the duration for the highest minimum fuel consumption is about 2.6 years.

The feasibility of relocating a small (~500,000 kg) Near-Earth Asteroid (NEA) to High Earth Orbit via Solar Electric Propulsion (SEP) is evaluated with the orbital simulation software General Mission Analysis Tool (GMAT). Using prior research as a basis for the mission parameters, a retrieval mission to NEA 2008 HU4 is simulated in two parts: approach from Earth and return of the Asteroid Redirect Vehicle (ARV) with the asteroid in tow. Success of such a mission would pave the way for future missions to larger NEAs and other deep space endeavors. It is shown that for a hypothetical launch time of 24 May 2016, the ARV could arrive within 25 km of 2008 HU4 on 28 Jun 2017 with a Delta V of 0.406 km/s, begin return maneuver on 08 Dec 2017 and reach Earth altitude of 450,000 km by 23 Apr 2026 with a Delta V of 44.639 m/s.

We investigate the spectra of asteroids at near- and mid-infrared wavelengths. In 2010 and 2011 we reported the detection of 3 ?m and 3.2-3.6 ?m signatures on (24) Themis and (65) Cybele indicative of water-ice and complex organics [1] [2] [3]. We further probed other primitive asteroids in the Cybele dynamical group and Themis family, finding diversity in the shape of their 3 ?m [4] [5] [6] and 10 ?m spectral features [4]. These differences indicated mineralogical and compositional variations within these asteroid populations. Also in the mid-infrared region we studied a larger population of asteroids belonging to the Bus C, D, and S taxanomic classes to understand the relationship between any mineralogy and hydration inferred in the visible and near- infrared with the shape, strength, and slope of the 10 ?m emission. We have discovered that at least 3 of the main Bus taxanomic groups (Cs, Ds, and Ss as defined by their visible spectra) clearly cluster into 3 statistically distinct groups based on their 8-13 ?m spectra. Additionally we have attempted to simulate in a laboratory the possible organic compounds we have detected on two asteroids, using various mixtures containing aromatic and aliphatic hydrocarbons. We find that asteroid (24) Themis and (65) Cybele have ?CH2/?CH3 and NCH2/NCH3 ratios similar to our 3- methylpentane, propane, and hexane residues, suggesting that the organics on these asteroids may be short chained and/or highly branched. The ?CH2/?CH3 and NCH2/NCH3 for asteroid(24)Themis are most consistent with the DISM, and some carbonaceous chondrites. The band centers of the C-H stretch absorptions indicate that both asteroids may have aliphatic carriers chemically bonded to electronegative groups (i.e. aromatics), and some that are not. We also detect a 3.45 ?m feature in the spectra of both asteroids that is present in several dense molecular clouds. Our results suggest an interstellar origin for the organics on (24) Themis, and likely (65) Cybele. The differences in the organics of Themis and Cybele are likely related to variations in thermal processing, irradiation and/or formation region in the solar nebula.