The SPS Electric Propulsion Lab

What is the SPS Lab all about?

The traditional laboratory courses offered by the U of A Physics Department provide an excellent training in basic physics. They are not, however, designed to teach students the types of skills that are necessary to perform real experimental work in a genuine physics research laboratory. (Note that this does not reflect any deficiency on the part of the Physics Department; funding has simply never been provided to the Department to teach this type of supplementary technical knowledge.) Beginning in the Fall of 1992, the members of the U of A Society of Physics Students (SPS) began discussing various "hands-on" projects to which we could devote ourselves in order to develop experimental physics skills. We found numerous opportunities to learn important skills by repairing or dismantling damaged equipment, but we found that students tended to lose interest in these types of projects fairly quickly. Consequently, we decided to choose a unifying theme to lend relevance to these tasks as well as to suggest opportunities for more complex student research projects. After examining numerous suggestions, the SPS members chose to pursue the investigation and construction of various types of electric propulsion systems.

What is Electric Propulsion?

Electric Propulsion involves the acceleration of ionized gases through the application of electromagnetic forces. It also represents the only practical method for rapid interplanetary travel currently known to mankind. While conventional rockets produce large amounts of thrust through the highly inefficient process of chemical combustion, such high thrust levels are only important for rapid planetary lift-off scenarios. A much more important characteristic for interplanetary travel is a quantity called specific impulse. Specific impulse is essentially an indication of how much a rocket's velocity can be increased by using a given quantity of fuel. Electrically propelled spacecraft generally possess very high values of specific impulse, allowing them to travel 10 to 100 times faster than chemical rockets with the same amount of fuel.

Why was Electric Propulsion chosen as a unifying theme?

A number of compelling advantages dictated the choice of this topic over several others that were being considered. While the immediate applicability of this technology to space exploration captured the imaginations of all of the students involved, it was also apparent that the design and construction of such devices would entail an interdisciplinary approach involving the application of classical mechanics, electromagnetism, modern physics, fluid dynamics and plasma physics. Additionally, by working together as a team to turn a theoretical design into a working electric thruster, it was apparent that students could develop technical expertise in such areas as soldering, the use of basic handtools, drilling, grinding, milling, lathing, tapping and polishing. Students would also learn about vacuum system construction and operation, the use of adhesives and lubricants, the testing and evaluation of electronic circuits, the implementation of computerized data acquisition techniques and the properties of various transducers and detectors.

What meaningful research can be done in the field of Electric Propulsion?

Formidable engineering challenges must still be addressed before the advantages of electric thrusters can be fully exploited. Most notably, thrust levels must be increased, power supply weights must be reduced and operational lifetimes must be extended. While extensive research was performed in the 1950's and 1960's on the use of electric propulsion for interplanetary spaceflight, many promising concepts had to be abandoned due to the technological limitations of the power conditioning systems in use at the time. To date no consistent effort has been made to reevaluate these approaches in light of modern power processing technologies. In fact, research into the development of electric thrusters for interplanetary travel has been largely abandoned by NASA and the scientific community since the late 1960's. It was at that time that the major focus of electric propulsion shifted from interplanetary missions to low-power near-earth applications such as orbit stabilization and directional control. This change arose when plans for large space power systems were abandoned in favor of the gradual development of large solar panels. By the end of the 1990's, however, megawatt space power systems will be readily available through the imminent declassification of systems developed for the Strategic Defense Initiative and the Department of Defense. Finally, many of the analytical problems that could not be solved with the computer technology available in the 1960's are now tractable using modern computer modeling techniques and hardware.

What is SPS doing with Electric Propulsion?

In order to provide an exciting theme to unify the projects that students perform in the SPS Lab, we have decided to focus on two aspects of electric propulsion: mission-enabling concepts for interplanetary travel and the development of high thrust electric propulsion launch systems that utilize microwave beamed power. Towards this end, we are interested in investigating a wide assortment of electrostatic, electromagnetic and hybrid electrothermal thrusters. We would also like to reassess some of the more speculative electric propulsion concepts abandoned in the 50's and 60's in light of modern power processing technologies and new technological developments. Naturally, we do not expect to become the first college students in history to revolutionize the nature of interplanetary travel in a few semesters. With the help of interested graduate students and professors, however, undergraduate students can construct electric thrusters based on designs previously published in the relevant literature. While this will not involve original research, it will acquaint students with the process of researching, building and testing a relatively complicated experimental device. We have found that, as students participate in this process, they try to find ways to modify the published design to improve the thruster's performance. While these ideas may not always bear fruit, by building an electric thruster to known specifications, the students will have prepared themselves to construct a fairly sophisticated experiment to test their own original ideas. With proper guidance from professors and graduate students, this can result in an immensely exciting undergraduate research experience.

Society of Physics Students