Masters Theses

Date of Award

12-1993

Degree Type

Thesis

Degree Name

Master of Science

Major

Aerospace Engineering

Major Professor

Gary A. Flandro

Committee Members

Robert Roach, Roy Schulz

Abstract

With decreasing natural resources here on Earth, new avenues must be explored which satisfy our consuming needs and provide a reasonable economic return. One such option is asteroid mining. An asteroid rendezvous mission is the first step in achieving this goal and may provide scientists with a deeper understanding of the formation of the solar system. The asteroid rendezvous mission must be technically and economically sound, and this will require that advanced propulsion systems be developed to reduce the cost of interplanetary travel and promote commercial involvement. The primary purpose of this thesis is to design and compare optimal rendezvous missions to Orpheus between the years 2000 - 2020 using different modes of propulsion. The options considered are chemical, nuclear thermal, nuclear electric, solar electric, and solar sail propulsion systems. Three ANSI C programs were written on Silicon Graphics workstations to model the three-dimensional interplanetary flight of spacecraft using these propulsion schemes. An impulsive thrust program was written which solves Lambert's problem using a modified Gauss algorithm developed by Battin. The selection of optimal impulsive missions is based on the trajectory with the lowest total energy (C3) requirement. The low thrust trajectory programs utilize Pontryagin's Maximum Principle to optimize the power-limited and solar sail rendezvous trajectories. Fuel is minimized in the power-limited missions, while minimum flight time is the optimizing criterion in the solar sail missions. The resulting two point boundary value problems are solved using two iterative methods: the method of Steepest Descent, and Newton's Method. The basis for comparison of the different propulsion schemes is the initial mass of the spacecraft injected into the transfer trajectory. All missions were designed to carry a net spacecraft mass of 250 kg. The minimum energy chemical mission is a 350 day opportunity with a launch date of January 31,2002. The total C3 and required rendezvous AV are 16.9824 (km/s)2 and 3.0084 km/s, respectively. The initial spacecraft mass for this mission is 1008.47 kg. The nuclear thermal propulsion (NTP) mission launches on the next optimal impulsive opportunity: January 31,2006. The corresponding energy requirement is 17.5308 (km/s)2 and the rendezvous AV is 3.1498 km/s. This mission also has a 350 day time of flight. The injected NTP spacecraft mass is 1588.37 kg, which is 57.50% greater than the chemical spacecraft mass. All low thrust missions analyzed in this thesis were found to have significant mass savings over the chemical mission. The lowest initial spacecraft mass was calculated for the NEP case with a flight time equal to the impulsive missions. The launch date for this minimum fuel opportunity is on July 22,2005, and the resulting initial mass of 406.63 kg is 69.68% less than the chemical mass. However, this mass is considered to be extremely optimistic and based on far-term assumptions. The other power-limited scheme considered in this study is solar electric propulsion. This option launches from Earth on June 30,2017 and arrives at Orpheus after 350 days on June 15,2018. The corresponding injected spacecraft mass is 736.84 kg, which is 26.93% less than that for the chemical mission. Solar sail propulsion provides the greatest mass benefit of the near-term schemes considered. The optimal sail mission has a launch date of March 27, 2018 and a flight time of 378 days, which is comparable to the impulsive transfer times. These results are given for a sail with a characteristic acceleration of 1 mm/s2 and translate into an initial spacecraft mass of 481.52 kg. This represents a mass savings of 52.25% over the optimal chemical spacecraft. Analysis of the various mission scenarios suggests that solar sail propulsion represents a viable near-term technology which offers large cost advantages over existing technologies. Also, due to the reusability of these sails, this propulsion scheme is ideally suited for asteroid mining. These combined factors may provide economically feasible interplanetary missions with commercial cooperation along with promoting further space exploration. The author therefore suggests that serious development programs for solar sail propulsion systems be initiated immediately.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS