Effect of Spacecraft Aerodynamics and Heat Shield Characteristics on Optimal Aeroassisted Transfer

Abstract

A spacecraft designed to operate in a planetary atmosphere must have an adequate heat shield to withstand the high heat fluxes and heat loads that are generated by aerodynamic heating. Very often, the mass of the thermal protection system is a significant fraction of the total mass of the vehicle. In contrast, performing maneuvers in the atmosphere, that would be very costly in terms of propellant consumption if they were performed completely outside of the atmosphere in a classic way, is a very attractive prospective technique. The advantages and disadvantages in terms of total mass spared must be determined. The mission investigated involves an aeroassisted coplanar transfer from a high to a low Earth orbit. The approach uses a combination of three propulsive impulses in space together with an aerodynamic maneuver in the atmosphere. The heat shield adopted is fully ablative, given the expected high values of the entering heat flux. The convenience of the aeroassisted maneuver and the influence of the parameters involved are evaluated in comparison to a conventional Hohmann transfer. In particular, a parametric analysis is performed by varying the following characteristics of the vehicle: aerodynamic efficiency, mass-to-surface ratio, deorbit impulse, and initial altitude of the orbit. The influence of the thermal protection system is examined by assessing the impact of the type of ablative material employed, the thermal safety factor, and the allowable temperature for the adhesive layer on the substructure. The analysis is conducted with a highly representative thermal model by coupling the dynamic and thermal analyses and using a genetic optimizer. The optimization methodology and the thermal model are completely original. The results indicate the importance of choosing low-density ablative materials, of adopting a suitable thermal safety factor, and of choosing high-performance adhesives. The optimal trajectories obtained correspond to a zero second propulsive impulse.

Coupled versus uncoupled optimal solutions for thermal and dynamic problems in spacecraft atmospheric flight

“…To obtain answers to the research questions described in the introduction, the objective of the study focuses on a more general optimization process. As mentioned, in recent studies (Mazzaracchio and Marchetti, 2012;Mazzaracchio, 2013aMazzaracchio, , 2013b, the author was interested in identifying the optimal combination of trajectories and related heat shield configurations, namely, the locations and thicknesses of the ablative and eventual reusable zone, for some classes of aeroassisted orbital maneuvers. These configurations maximized the payload mass transported by a given spacecraft.…”

“…Even this choice is related to the reduction of the computational load, with a consequent impact at the level of representativity. The optimization of the aeroassisted orbital maneuvers and of the heat shields of space vehicles has been addressed by the author (Mazzaracchio and Marchetti, 2010;Mazzaracchio and Marchetti, 2012;Mazzaracchio, 2013aMazzaracchio, , 2013b) using an original and highly representative model of the heat shields. In the 2010 and 2012 papers, the analysis was conducted by coupling the thermal and dynamic problems, whereas the study was performed with decoupling in the 2013 paper.…”