Optimal low-thrust trajectories to asteroids through an algorithm based on differential dynamic programming

In this paper an optimisation algorithm based on Differential Dynamic Programming is applied to the design of rendezvous and fly-by trajectories to near Earth objects. Differential dynamic programming is a successive approximation technique that computes a feedback control law in correspondence of a fixed number of decision times. In this way the high dimensional problem characteristic of low-thrust optimisation is reduced into a series of small dimensional problems. The proposed method exploits the stage-wise approach to incorporate an adaptive refinement of the discretisation mesh within the optimisation process. A particular interpolation technique was used to preserve the feedback nature of the control law, thus improving robustness against some approximation errors introduced during the adaptation process. The algorithm implements global variations of the control law, which ensure a further increase in robustness. The results presented show how the proposed approach is capable of fully exploiting the multi-body dynamics of the problem; in fact, in one of the study cases, a fly-by of the Earth is scheduled, which was not included in the first guess solution

Pentanol isomer synthesis in engineered microorganisms

Pentanol isomers such as 2-methyl-1-butanol and 3-methyl-1-butanol are a useful class of chemicals with a potential application as biofuels. They are found as natural by-products of microbial fermentations from amino acid substrates. However, the production titer and yield of the natural processes are too low to be considered for practical applications. Through metabolic engineering, microbial strains for the production of these isomers have been developed, as well as that for 1-pentanol and pentenol. Although the current production levels are still too low for immediate industrial applications, the approach holds significant promise for major breakthroughs in production efficiency

ISS leak localization using attitude response

ABSTRACT This paper presents a new method to localize air leaks on the International Space Station based on the spacecraft attitude and rate behavior produced by a mass expulsion force of the leaking air. Thrust arising from the leak generates a disturbance torque, which is estimated using a real-time predictive filter with a dynamical model (including external disturbances such as aerodynamic drag and gravity-gradient). The leak location can be found by estimating the moment arm of the estimated disturbance torque, assuming that leak is caused by only one hole. Knowledge of the leak thrust magnitude and its resulting disturbance torque are needed to estimate the moment arm. The leak thrust direction is assumed to be perpendicular to the structure surface and its magnitude is determined using a Kalman filter with a nozzle dynamics model. There may be multiple leak locations for a given response, but the actual geometric structure of the space station eliminates many of the possible * Graduate Student, Student Member AIAA