UNDERSTANDING AND IMPROVING UPON ELECTRODYNAMIC DUST SHIELD TECHNOLOGY ON A LUNAR ROVER

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1 UNDERSTANDING AND IMPROVING UPON ELECTRODYNAMIC DUST SHIELD TECHNOLOGY ON A LUNAR ROVER Jordan Olive The University of Hawaii at Hilo Fellow Hawaii NASA Space Grant Consortium 2 nd Summer 2009: Final Report ABSTRACT Electrodynamic dust shield technology being researched in the Electrostatic and Surface Physics Laboratory at Kennedy Space Center is being adapted for use on an optical surface in a lunar environment. The tread driven design of the rover and placement of the camera between the treads warrants the need for an active dust deflection system. This paper will discuss techniques we used to test and better understand the workings of the electrodynamic dust shield in space. INTRODUCTION The Lunar Micro-Rover (LMR) project is currently underway at Ames Research Center. The purpose of this project is to create a relatively low cost universal lunar robotic platform. The rover itself is approximately 35 cm long, 25 cm wide, and 15 cm tall. It has Teflon treads with Kevlar rope sewn on for grip. A camera is mounted in the chassis between the treads at the front of the rover with a glass window to look through. The camera will be used for both real time tele-operated driving as well as for taking high resolution images. A dust deflection system is needed to ensure that clear images can be continuously taken even while lunar regolith is stirred up and tossed around by the treads. The surface of the moon can be described as a combination of fine dust and rocks. Most of the surface consists of a fine dust known as Lunar regolith, which has a bulk density of about 1.5 g/cm 3. According to The Lunar Sourcebook roughly 10 to 20 percent of the [lunar] soil is finer than 20 μm, and a thin layer of dust adheres electrostatically to everything it contacts: spacesuits, tools, equipment, and lenses. In general, the particles are somewhat elongated and are angular to sub-angular. Summer 08 was spent researching different solutions to remove lunar regolith from the camera lens. Methods like electromagnets and sacrificial lens to the currently implemented electrodynamic dust shield were researched. The electrodynamic shield was developed to ensure clear vision and the success of the mission. Low current operating conditions make it the ideal option to use on the lunar micro rover due to the limited battery capacity. NASA places safety on the highest of priorities on safety. To get a device such as the dust shield qualified to be implemented on a rover, many safety tests must be conducted.

2 My fellowship project of 2009 spring term was spent testing different variables to optimize the effectiveness of the dust shield. All of these variables were tested in normal atmospheric pressures instead of space conditions. After this semesters work, I am confident in saying that the most efficient clearing factor was reached at 5 kilovolts, 5 Hertz, and a wave form of a square wave. SUMMARY OF WORK This past summer 09 was spent testing and redesigning the electrodynamic dust shield to work in a zero atmospheric environment (a, simulating outer space). Testing included multiple test varying the voltage, waveform, and frequency. Questions like; Will the dust shield short? Will the effectiveness be affected? Is clippage in RC (resistor-capacitor) circuit affected? After all data was gathered a circuit was made to match the new data. This information is important to ensure that this new experimental technology that is being used in the lunar micro rover is independent and won t interfere with other systems. The new tests in a qualify the dust shield for the long space qualification test. After the circuit was completed, a 1 ½ x 1 ½ aluminum molding was designed to both hold the device secure and distribute heat. With the new casing the dust shield went under a series of test were it had to withstand temperatures ranging from 107 C to -153 C while operating for a period of two hours in a thermo chamber. Before the device could be qualified for space and implementation into the rover, it had to go through a EMST (electro-magnetic test) where it was pulsed with 20amps at 12 volts to make sure circuit protection worker properly. METHODS The current power source I am using is Pico Electronics High Voltage DC-DC power supply. For the clear circuit, I am using Indium tin oxide, currently at 8-12ohms per square foot. Tests were run in both a and non chamber where outside factors and space were simulated. I am using an electronic scale that measures out to the thousandths of a gram to measure and calculate the effectiveness of the dust repeller. The formula I am using to calculate the efficiency is: CF: Clearing Factor Mi: Initial Weight of Dust Mf: Weight of Dust after the use of the device. Figure 1: clearing factor formula

3 DISCUSSION / DATA ANALYSIS Each of the following graphs were tested a total of ten times. And then the average was calculated to figure out the mean efficiency using the Clearing factor formula. VOLTAGE DATA Purpose: Due to less resistance because of the absent of air in space, the arcing distance of voltage is decreased. Meaning electrodes have to be further spaced in order to prevent shorting. Questions that needed to be answered: Will the dust shield short? Will the effectiveness be affected? Frequency (Hz) Voltage (v) Effectiveness (grams removed) Non Non age in 5 5, % 87.3% 5 6, % 67% 5 7, % 50% 5 8, % 3% Results: Spacing was enough to keep device from shorting. However we did see a decrease in effectiveness while using 5kvs and an increase while using 6kvs. FREQUENCY DATA Purpose: To test if frequency data from non differed from tested data.

4 Frequency (Hz) Voltage (v) Effectiveness (grams removed) Non Non age in 5 5, % 91.2% 7 5, % 85.1% 15 5, % 77.2% 30 5, % 45.2% 60 5, , % 2.8% Results: Testing data hardly differed when varying the frequency, infact the device seemed to work better by a 0.5% increase in effectiveness. WAVEFORM DATA Purpose: To test if clippage due to the certain types of waveform affected the overall performance. The decrease in resistance due to the lack of air in space could change the delay cycle caused in the RC (resistor-capacitor) circuit. Wave Form Voltage (v) Effectiveness (grams removed) Non Non In Square 5, % 92.9% Sino 5, % 68.3% Triangle 5, % 30%

5 Results: Square waved seemed to not be affected while both the sinowave and triangle waves experienced a drop in performance. Overall Results: After comparing both and non test, I am confident in saying that the optimal operating conditions are 5 kilovolts, 5 Hertz, and a wave form of a square wave. FINAL CIRCUIT The final circuit has the capabilities to vary Voltage, Frequency, Waveform and the radio control. Figure 10: Picture of final circuit and pictures of the real circuit on vector boards.

6 CONCLUSION In conclusion, I have successfully made a prototype that accomplishes the task at hand - to design a dust deflection shield which is light in weight, repels dust, draws low current, and is small enough to fit into the lunar micro rover. Test results both in a non- and point towards the same optimal operating conditions of 5 kilovolts, 5 Hertz, and a wave form of a square wave. After being tested in a chamber the following conclusions were made: 1) Spacing was enough to keep device from shorting. However we did see a decrease in effectiveness while using 5kvs and an increase while using 6kvs. 2) Testing data hardly differed when varying the frequency, infact the device seemed to work better by a 0.5% increase in effectiveness. 3) Square waved seemed to not be affected while both the sinowave and triangle waves experienced a drop in performance. After these test were verified and now that we were sure that the dust shield was optimized, we created a final circuit with this data. After a series of test, including temperature test, protection test, and static test it was implemented in the rover. The electrodynamic dust shield is officially space qualified and is being used in prototype 6 of the lunar micro rover. ACKNOWLEDGEMENTS Thanks goes out to my outstanding mentor Riley Ceria who guided me through my fellowship project this term. Also to the outstanding staff at the Hawaii Space Grant Consortium who made this awesome experience available. And more specifically to the following: Riley Ceria Mentor, Robotics Advisor for the College of Engineering, UH Manoa Marcia Rei Sistoso Program Advisor, Hawaii Space Grant Consortium Edward Scott Associate Director for Fellowships, Hawaii Space Grant Consortium Sun Park Advisor, University of Hawaii at Hilo Art Kimura & Rene Kimura Future Flight Director and Education Specialist, Hawaii Space Grant Consortium