MEMS Megapixel microthruster array l AFOSR Tech Sat21

MEMS Mega-pixel microthruster array l AFOSR Tech. Sat-21 # F 49620 -99 -C-0012 – Honeywell: Dan Youngner, Son Thai Lu – Princeton: Edgar Choueiri – $~160 K for ~18 months MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 1

Satellites: The traditional vision l l l Big Expensive Single, connected unit MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 2

Not all parts of huge satellites are necessary for all missions l Antennas: Only need elements along periphery, other key locations MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 3

Micro-satellites: The new vision l l l Cluster / network that behaves as one “Virtual satellite” Effective size = 100’s m x 100’s m Smaller Cheaper Robust » redundant parts » if one dies, another wakes up to take its place MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 4

What are “small” satellites? l l Football-size ~10 kg Shorter missions They are the future Source: NASA MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 5

Micro-satellite relative motion l Issue : Satellites in cluster don’t stay put with respect to one another MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 6

Hill Orbitals: Manageable chaos (if only it were that simple) l Ideal world: microsatellites orbit one another in perfect “Hill orbitals” » complicated, but manageable l l Real world: They don’t Continual/ periodic station-keeping required » to adjust position » to adjust orientation MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 7

Micro-thrusters on Micro-satellites l Conceptual Honeywell Satellite (H -Sat 101) targeted for 2003 deployment (Jack Jacobs) MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 8

The Vision: A million separate one-shot engines on a chip l l Co-axial stack of 4 silicon MEMS wafers Wafer #1: array of 1 million pixel igniters Wafers #2 & #3: arrays of 1 million coaxial hollow fuel/oxidizer filled cavities Wafer #4: Egress channels MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 9

Thruster array: scale =~100: 1 l Wafer thickness = cavity length = 250 mm l Cavity width = ~40 - 135 mm Single thruster MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 Array of thrusters p 10

The igniter arrays l l l Mature Honeywell product: IR scene projector arrays (10 yr, $10 M) Rad-hard RICMOS underlayers for address / drive 512 x 512 arrays: TM » up to 2 m. W/pixel l Temps to ˜ 900°C in ˜ 10 msec (in std vacuum package) l Other arrays: » up to 100 m. W/pixel 4 -inch wafer containing four 512 x 512 pixel arrays, eight 128 x 128 pixel arrays, and several emitter and FET test structures. MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 SEM photo of pixels. Each pixel is 51µ x 51µ (center to center) p 11

IR Scene Projector Display l Synthetic infra-red scene of rocket MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 12

Wall Rupture Strength: FEM l l Finite element modeling Assumes 100 atmosphere explosion in chamber MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 13

Wall Rupture Strength: Summary l Wall strength: » function of wall thickness » function of radius of curvature » function of wall roughness » function of silicon yield strength MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 14

Si. N Diaphragm Rupture Strength l Function of thickness, radius, material properties MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 15

Cavity shapes & dimensions l Optimal design unknown l When in doubt, build them all MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 16

Fuel-filled cavity arrays l l l RIE holes through silicon wafers Etch-stop on thin Si. N diaphragm Fill cavities with fuel, oxidizers » » l l Iso Propyl alcohol sodium azide (Na. N 3) Na in Benzophenone Phosphorus in Carbon Disulfide Wafer-to-wafer bond Many variations of cavity size, shape, space Diaphragms fracturing during wafer dicing SEM photos of cavities etched into 250µm Si wafer. MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 17

Filling cavities with fluids l Procedure for filling cavities: » pump chamber to <1 torr base pressure » cool die to ~77ºK » open valve, disbursing fluid » back-fill chamber with dry N 2, keeping puddle on die » warm die to room temp MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 18

Low Temp Bonding of Fuel / Oxidizer Wafers l Requirements: » low temp – don’t ignite fuels – don’t rupture diaphragms » bonds when wet – with methanol – with other fuels/oxidizers l » inert wrt fuels / oxidizers Approach: » Gallium solder (melts at 29. 8 C) – evaporated onto -55 C substrate (Jeff Ridley) » Gold as seal (eutectic with Ga) » l Excellent mutual soluability Status: » Under development, promising – – eutectic forms Ga/Au seal is strong alignment is difficult diffusion barriers / adhesion layers still an issue MEMS Mega-pixel Microthruster Array. Looking through Pyrex wafer at Ga-Au seal on Gold wafer Cavities are empty; Region around the cavities are filled with water Honeywell / Princeton. F 49620 -99 -C-0012 p 19

Low temperature ignition l l l <160°C max ignition temp Strategy: Hypergolic fuel/oxidizer combination choice is still under evaluation MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 20

Interim Strategy: Laser Ignition l Issues with electrical ignition: » BRITE wafers are rare, high-priced – (1 @ $30 K) » Available power from BRITE is low (~1. 6 m. W) – too low to initiate some reactions l Solution: Pyrex wafers + YAG laser » Pyrex is abundant, optically transparent » YAG laser: ~100 k. W for ~6 nsec (0. 6 m. J) – more than enough to initiate all conceivable reactions MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 21

Expected Performance of Pixel Array * Estimated performance based on standard chemical explosion characteristics. Subject to further modeling and verification. ** Data from “Electric Propulsion for Low Earth Orbit Communication Satellites, ” by Steven R. Oleson, NASA Lewis Research Center, 1997. MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 22

Testing l l l To be performed by Professor Choueiri, Princeton. Electric Propulsion and Plasma Dynamics Lab (EPPDy. L) Large (8 ft dia x 24 ft long vacuum tank @ 1 E-5 torr Laser interferometric measurements more information at: http: //cougarxp. princeton. edu: 2112/eppdyl/personnel/eyc. html MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 23

Similar Technologies l l Carol Rossi & Kris Pister: BSAC & LAAS, France » thermally ignite explosive trapped in pixel » patented, demonstrated » designed primarily for drug dispensing » issues: low density (3 mm x 3 mm) David H. Lewis: TRW » MCNC MUMPS fab » 19 thrusters on 6 mm x 6 mm square » thermally boil liquid. » issues: Low density, Low Isp, thermal fratricide MEMS Mega-pixel Microthruster Array. http: //bsac. berkeley. edu/microrockets. html http: //design. caltech. edu/micropropulsion Honeywell / Princeton. F 49620 -99 -C-0012 p 24

MEMS Mega-pixel Microthruster Array Status Anticipate 1 st testable structure by March, 2000. l … stay tuned. l MEMS Mega-pixel Microthruster Array. Honeywell / Princeton. F 49620 -99 -C-0012 p 25