MEMS Microthruster Digital Propulsion System June, 1998 MEMS - - PowerPoint PPT Presentation

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MEMS Microthruster Digital Propulsion System June, 1998 MEMS - - PowerPoint PPT Presentation

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DARPA MEMS Microthruster Digital Propulsion System June, 1998 MEMS Principal Investigators Meeting Dr. David H. Lewis, Program Manager & PI TRW Space & Electronics Group Redondo Beach, CA Dr. Erik K. Antonsson, PI Dr.

slide-1
SLIDE 1

DARPA

  • 9800217-1002- 1 -NT

MEMS Microthruster Digital Propulsion System

  • Dr. David H. Lewis, Program Manager & PI

TRW Space & Electronics Group Redondo Beach, CA

  • Dr. Erik K. Antonsson, PI

California Institute of Technology Pasadena, CA

  • Dr. Siegfried W. Janson, PI

Aerospace Corp. El Segundo, CA

June, 1998 MEMS Principal Investigator’s Meeting

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SLIDE 2

DARPA

  • 9800217-1002- 2 -NT

MEMS Technologies Support Future Space Systems

  • Distributed proliferated systems have multiple

applications – Large apperture – Long baseline – Communication – Interceptors

  • Low mass nanosats combined with MEMS

Digital Propulsion has system advantages – Several MEMS Digital Propusion implementations can be identified

  • Isp:<250 sec, resistojet
  • Isp:<250-300 sec, solid propellant
  • Isp:300+-450 sec, bi-propellant
  • Isp:1,000+ sec, PPT’s

– Efficient packaging - no valves, lines or structure

Concept Sketch of Microsatellite Constellation Interceptor ²V Increase Improves as Isp Increases

Propellant Mass Fraction Deliverable delta V (km/s) 1 2 3 4 5 6 0.2 0.4 0.6 0.8 1 Isp =1000 400 300 200 100 50

  • ²V/Isp g0

Mfinal Minitial =e

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SLIDE 3

DARPA

  • 9800217-1002- 3 -NT

Exploded View of Digital Microthruster Array

Top Die Diaphragms on bottom, expansion nozzles on top Middle Die Propellant fills individual holes Bottom Die Polysilicon “ignitors” with direct inter- connects to bond pads (no electronics)

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SLIDE 4

DARPA

  • 9800217-1002- 4 -NT

Top View of Phase 1 Thruster Stack

6 mm square 400-micron thick top wafer 15 thrusters in a 3 x 5 array Bond pads Alignment Holes

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SLIDE 5

DARPA

  • 9800217-1002- 5 -NT

Assembled Phase 1 “Thruster Chip”

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SLIDE 6

DARPA

  • 9800217-1002- 6 -NT

Fabrication Issues

  • Combustible solid:

– Ignitor design; 20 x 400 µ resistors required for lead styphnate – Resistors must be thermally-isolated from substrate yet be mechanically robust – Bonds must withstand high transient pressure

  • Resistojet:

– No inter-chamber leaks – Bonds must withstand ~ 600 K temperature

  • Electrolysis rocket:

– No inter-chamber leaks

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SLIDE 7

DARPA

  • 9800217-1002- 7 -NT

Fabrication Issues

  • Nozzle array:

– Mechanical dicing requires diaphragm protection

  • Propellant die:

– Planarity of baked FOTURAN – CTE mismatch to silicon; bonding agent required – Filling die with propellant; use solids if possible

  • Electronics die:

– Thermal isolation of resistors using standard CMOS SiO2 layer thickness; reduce power requirements – High voltage (>100 V) for spark generation

  • Bonding die:

– Cyanoacrylate cannot tolerate high temperatures – Epoxies require controlled deposition (screen printing)

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SLIDE 8

DARPA

  • 9800217-1002- 8 -NT

Laser Exposure of Glass Spacer Dice

Individual die separate during the HF etch

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SLIDE 9

DARPA

  • 9800217-1002- 9 -NT

20 x 400 Resistor

The polysilicon heater element is 20 microns wide, 0.5 microns thick, and has a resistance of 210 Ohms. We apply 30 Volts and it glows red.

3 m SiO2 Polysilicon 0.5 micron thick Gold 0.5 micron thick

46 MICRONS 29 MICRONS 41 MICRONS 22 MICRONS 32 MICRONS 20 MICRONS 29 MICRONS 41 MICRONS 180 MICRONS 46 MICRONS 180 MICRONS 100 MICRONS 120 MICRONS 188 MICRONS

SILICON SUBSTRATE

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SLIDE 10

DARPA

  • 9800217-1002- 10 -NT

High Speed Video Images of Polysilicon Resistor Firing

t = 0 msec t = 25 msec t = 49 msec t = 74 msec t = 98 msec t = 123 msec t = 148 msec t = 173 msec

  • With 60 volts input, the 20 x 400 resistor fires for ~50 msec
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SLIDE 11

DARPA

  • 9800217-1002- 11 -NT
  • Ballistic pendulum thrust stand
  • f 240 gram mass
  • Impulse range: 10-6 to 10-3 N-s
  • Laser interferometric position

measurement

  • Active magnetic damping
  • Basic Stamp microcontroller
  • In-vacuum calibration

Thrust Stand

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SLIDE 12

DARPA

  • 9800217-1002- 12 -NT

Videotapes

  • Resistor glow
  • Ignition of thin propellant layers

– Nitrocellulose using kilovolt AC in resistors – Lead styphnate using 32 V DC in resistor

  • Electrolysis
  • Solid thruster ignition
  • Thrust stand firing
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SLIDE 13

DARPA

  • 9800217-1002- 13 -NT

Summary

  • Combustible solid, resistojet, and electrolysis microthrusters

demonstrated – All three viable with specific propellants

  • Initial problems:

– Poor ignition of typical solid propellants – Weak bond strength at high temperatures – Inter-chamber leaks for glue-bonded layers

  • Thrust stand is ready

– Customize power drivers for different power requirements (solid, resistojet, electrolysis)

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SLIDE 14

DARPA

  • 9800217-1002- 14 -NT

Digital Propulsion Concept is Refined Through Three Hardware Builds

Task 5. MEMS Microthruster Propulsion System Task 1. Proof of Concept

  • Design
  • Fab

Task 2. Sub-Array Evaluations Task 3. Full-Array Demonstration

  • Design
  • Fab
  • Commercial foundry builds
  • Management
  • Reporting
  • Test
  • Characterize

3 Configurations 2 Test Articles

  • Design
  • Fab
  • Test
  • Characterize
  • Test
  • Characterize

1 Test Articles Task 4. Process Models and Analyses Downselect Downselect

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