Physically Idealized Human Rated Rocket Based Interplanetary Transportation System (PHRITS)

"The choice, as Wells once said, is the Universe - or nothing... The challenge of the great spaces between the worlds is a stupendous one; but if we fail to meet it, the story of our race will be drawing to its close. Humanity will have turned its back upon the still untrodden heights and will be descending again the long slope that stretches, across a thousand million years of time, down to the shores of the primeval sea."

Arthur C. Clarke, in his book "Interplanetary Flight", 1950

Introduction

Many alternative types of rocket propulsion have been proposed in the scientific and engineering communities, ranging from the evolutionary development of proven concepts, to radical approaches requiring spacecraft of massive size, utilizing exotic power sources. This highly diverse pool of ideas is largely technology driven, and new concepts inevitably inherit the limitations of the underlying technology which spawned their conception.

Physically Idealized Rocket Based Propulsion

My PhD research investigates the concept of reaction based propulsion in its most fundamental terms, and aims to extrapolate from basic principles the design of the most capable, interplanetary transportation system (ITS) as it is possible with today's understanding of physics. No engineering restrictions are imposed, unless required to define the system. For example, physically ideal energy conversion methods are assumed, capable of converting all available fuel into energy at the maximum theoretical efficiency, regardless of whether or not technology can provide such a device. However, the system is required to provide transport while maintaining acceleration levels appropriate for a human crew. Within the constraints necessary to define the problem, nature has already provided a single, most capable solution. It is the goal of this research to identify this ideal solution to the stated problem of human transport within the solar system. The resulting design of the physically ideal, human-capable, reaction based, interplanetary transportation system (PHRITS) is envisioned to serve as a guide for all other technology bases, pointing the way towards maximum utilization of their potential.

Downloads

PHRITS was implemented as a distributed computing application (similiar to SETI@Home). While my work does not require thousands of contributors, I did welcome anybody who wished to donate CPU time (mostly friends and family).

For the interested reader, a number of further resources are also available. The table below lists all publications I have authored in conjunction with this work, including my dissertation.

In the process of working the problem, I had to collect and/or develop a good number of computational tools (see the LDCF paper for details). Some of the more interesting components can be downloaded directly below.

P.H.R.I.T.S. Software
GA Toolbox	[url]	PHRITS uses a Genetic Algorithm (GA) toolbox for Matlab, developed at the University of Sheffield (UK). The link will take you the main website. The code is also included in the PHRITS source.
SolvOpt	[url]	This is a Matlab based NLP solver, developed in Austria. The link takes you their main website.
MySQL	[url]	This link will take you to the MySQL website. MySQL is teh database used in the PHRITS distributed computing setup.
MySQL Matlab DLL	[url]	In order for Matlab to communicate with the MySQL database, you can either spend lots of money for a commercial ODBC driver, or make use of this freely distributed matlab dll, developed at the University of Toronto (CA).
MySQL Matlab Function	[10 kB]	The MySQL Matlab dll listed above has the limitation that it only supports the use of strings when inserting or retrieving data to/from the databse. This function pair works around this limitation, but representing any Matlab variable type by the string a user would have to type in the command window to create the variable. The original variable is recovered by use of the Matlab eval() command.
rsync	[url]	rsync is a utility for synchronizing file structures between two different locations, which can be located on different machines across a network. Within PHRITS, rsync is used to keep all active clients updated as changes are made to the code. The link takes you to the rsync home page.
P.H.R.I.T.S. Publications
Identification of the Physically Idealized Human Rated Rocket Based Interplanetary Transportation System (PHRITS)		My complete PhD dissertation - 300+ pages.
Low Cost Distributed Computing Framework for Large Option Space Trade Studies		This describes the computational tools used to implement the PHRITS research.
Using Physical Idealization to remove Technology Bias from Conceptual Trade Studies		This paper describes the core concept of physical idealization employed in the PHRITS research.
Polynomial Initial Guess Algorithm for Trajectory Solvers / Optimizers		This paper describes a polynomial based initial guess algorithm used in the PHRITS research to generate the required trajectory starting points with minimal human intervention.

Results

All this work did arrive at a conclusion, and it was actually pretty interesting. The concepts that PHRITS investigated were constructed from selections (design-choices) in three areas: (1) method of momentum exchange, (2) method of energy storage/production, and (3) material storage vs. collection during flight. After analyzing some 18000 concepts, the evolution of concepts settled on a population as shown in the figure below. Internal storage of both propellant and fuel were clearly favored over collecting it on-route (e.g. solar power).

The best power source was not that with the highest energy density, but a combination of methods in very specific proportions. This was a result of the interaction between the power generation and the impulse generation systems. For impulse generation (or momentum exchange), a thermodynamic nozzle was the favorite but again only if used in combination with other choices in specific proportions. The numbers for the highest scoring concept (ID 15958) are also shown below. The key message to take away from this was: even when looking just at the physics of rocketry, there is no clear single best solution (e.g. nuclear thermal, solar electic, etc.), but a combination of methods provides the best overall performance. The specific proportions of each sub-system are then dictated by the mission requirements imposed on the system. There's a lot more that can be gleaned from the data, read the discussion/conclusion in my dissertation if you are interested.