Tribo - dispenser Ground Test

1. Tribo-dispenser Ground Test International Symposium on Asteroid Mitigation and Exploration 5 April 2011

2. Authors John Guthery - Dean Ellis - Zach Itkoe- SumitPokhrel - Paul Braden - Katherine Westhoff - Luke Krehbiel Texas A&M College of Engineering

3. Outline • Purpose • Background • The Tribo-dispenser • Experiment Schematic • Experimental Setup • Pictures • Progress to Date • Data • Data Collection Process • Taguchi’s Method Description • Test Parameters • Future Work

4. Purpose • Retire the risks of tribo-dispensing technology as applied to albedo change mitigation technique • Collect test data on key parameters such as mass flow rate, charge mass ratio, and coverage effectiveness • Correlate test results with analytical models • Scale/redesign tribo-systems for space flight conditions

5. Background Spacecraft points the SATS directly toward the sun-lit side of Apophis. sun Negatively charged ACPs are directed with cone angle and dispensing speed carefully controlled so that ACPs neither go into orbit nor escape. Negative charge on ACPs ensures they will be attracted to the positively charged sun lit portions of the surface and repelled by the shadowed areas. Deposition can occur even with oblong, rapidly rotating asteroids with zero or negative surface gravity. ACPs are sized to prevent levitation even without adhesion. Once contact with the hot sun-lit surface is made, ACPs stick and begin to cure. They melt and bond with the surface, forming a thin, opaque coating. 5 Apophis

6. The Tribo-Dispenser for Albedo Change Treatment The ACP storage chamber is double-walled; the ACPs being contained within the inner wall. The inner wall is perforated by many small holes. A secondary flow is released into the outer portion of the selected ACP chamber The gas flows through the holes in the inner wall, both “fluidizing” the ACP mass (mixing up the ACPs so that the dry powder behaves like a liquid) and expelling a steady stream of ACPs into the mixing chamber. Fluidization stream ACP Chamber Albedo Change Particles Pressurized Inert Gas Tribo ionization tube Mixing Chamber The main flow out of the gas supply leads directly to the mixing chamber. Once mixed, the ACPs plus gas is forced through the narrow tribo ionization tube

7. Experiment Schematic Thermistor Camera Lamp Faraday cage SATS Infrared heater Nozzle Tribo-tube of SATS Aluminum plate capacitor Table Electrometer Compress-ed air tank • Not shown: • - DAQ + Computers • Scale (to measure mass of SATS before and after each run as well as mass of plate before and after each run)

8. Modeled Experimental Setup Heater Camera Aluminum plate Tribo-dispenser Test stand Projector SolidWorks model of preliminary test setup – used to determine initial sizing for test stand

9. Actual Experimental Setup Dispenser Mount Tribo-dispenser Heater Aluminum plate (not shown) Camera Slide rails Projector Test stand with available components in place

10. Actual Experimental Setup To the left: horizontal distance is adjustable via slide rails (circled) To the right: vertical height and pitch angle are adjustable on the dispenser mount Three degree-of-freedom dispenser mount

11. Progress to Date • Assembled initial models of the steps in the dispensing process • Pressurant chamber blowdown dynamics • Dual phase, gas/particle flow dynamics • Particle charge dynamics • Completed preliminary design of test hardware • Assembled and integrated 75% of hardware • Began initial testing

12. Data • Initial tests showed diminishing mass flow results • To counter this, the hopper was shaken before each test run to restart the fluidization • This gave more consistent data • Further tests are required to formulate a better model for the dispensing Without shaking the Hopper Shaking the Hopper

13. Data Collection Process Spraying ACPs into receptacle Accumulated ACPs Particle spray pattern from dispenser nozzle Tribo-dispenser control unit with hopper (circled)

14. Taguchi’s Method Description • Classical method has to test for every permutation of a set of variables because it assumes ALL variable interactions are important! • Orthogonal array/Taguchi Method assumes interactions between variables are negligible unless otherwise stated. • To find the optimal configuration, an equation can be written, where yk = kth trial result of output (can be Q/M, albedo, FPTE, A/M) a = coefficients to be determined. Note that ai also applies to double coefficients xi = 1 (for maximum input value) or -1 (for minimum input value)

15. Test Parameters Using the Taguchi’s method the possible tests were reduced from 256 different experiments that need to be repeated 3 times down to 16 that each need to be repeated 3 times using these 8 parameters

16. Future Work • Improving the data collect process • Repeat tests with different initial variables • Length and diameter of tribo-dispenser tube • Nozzle shape • Source pressures • Target distance and angle • Target’s charge • Conduct a thermal vacuum chamber test as well as a microgravity experiment