Masters Theses

Date of Award

8-1993

Degree Type

Thesis

Degree Name

Master of Science

Major

Aerospace Engineering

Major Professor

Gary A. Flandro

Committee Members

Robert Roach, Roy Schulz

Abstract

In order to make interplanetary exploration and exploitation feasible, the cost of interplanetary flight needs to be reduced. Two possible means of reducing this cost are nuclear thermal propulsion and solar sails. The primary purpose of this thesis is to develop optimal missions for chemical, nuclear thermal, and solar sail propulsion systems and then perform a comparison in order to demonstrate the need to develop these technologies.

In order to model these systems, two programs were written for use with high end Macintosh desktop computers and Silicone Graphics Iris workstations that modeled the interplanetary flight (in three dimensions) of spacecraft using these propulsion systems. The impulsive thrust program utilizes Battin's modified Gauss algorithm to solve Lambet's problem with a patched conic approximation. The low thrust program utilizes the iterative procedures of the method of steepest descent and Newton's method to solve the two-point boundary problem that arises from the application of Pontryagin's Maximum Principle to optimize solar sail trajectories. Methods of low thrust trajectory optimization are not available in standard texts, therefore the theory and application of this second program are given in great detail.

The criteria of comparison between the various vehicles were initial mass in low earth orbit (IMLEO) and mission duration. The mission was defined as the transport of 100 MT of usable payload from earth to Mars and the return of 50 MT with a minimum stay on the Martian surface of 30 days. The impulsive thrust vehicles are found to have a 427 day sprint mission with minimum energy cost on April 13, 2018. The IMLEO for the chemical mission is 19, 036.05 MT, a highly restrictive quantity. An acceptance of the health and reliability hazards of longer missions or development of additional technology such as aerobraking would be required to make this option viable. The IMLEO for the nuclear thermal system with the same mission is 2, 013.77 MT; this is 10.58% of the mass needed for the chemical system. The solar sail was found to have a time-optimal 923 day mission opportunity on June 1, 2018. The IMLEO for this solar sail mission with a chemical booster stage to provide earth escape is 452.24 MT. This is 22.46% of the mass required by NTP and only 2.38% of the mass required by chemical propulsion. An added benefit is that all of the mass excepting the chemical booster is returnable and presumably reusable. However, the lengthy mission time required by the sail indicates that it would be best used in support of a permanent exploitation of Mars (a "cycler" cargo ferry) or in an effort to reduce IMLEO of a chemical or nuclear thermal exploration mission (a cargo vessel carrying all supplies not needed to sustain the crew).

Because of the tremendous opportunities for cost savings presented by nuclear thermal propulsion and solar sails, research and development of both technologies should be restarted. Interplanetary travel via chemical propulsion is not currently a viable option and existence of these systems could be the key to making exploration and exploitation of Mars an achievable goal.

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