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High-Contrast Lab Contamination Control Plan

Based on the DeMi CubeSat contamination control plan by MIT STAR Lab team members Ewan Douglas and Rachel Morgan (MIT)

NASA source document: NASA Marshall Contamination Control of Space Optical Systems (also from https://extapps.ksc.nasa.gov/Reliability/Documents/Preferred_Practices/1263.pdf)

Examples: Hanford Contamination Control Update 2

References: Morzinski, Katie M., Andrew P. Norton, Julia W. Evans, Layra Reza, Scott A. Severson, Daren Dillon, Marc Reinig, Donald T. Gavel, Steven Cornelissen, and Bruce A. Macintosh. 2012. “MEMS Practice: From the Lab to the Telescope.” In SPIE MOEMS-MEMS, 825304–825304. http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1344856.

Gushwa, K. E., & Torrie, C. I. (2014). Coming clean: understanding and mitigating optical contamination and laser induced damage in advanced LIGO. In G. J. Exarhos, V. E. Gruzdev, J. A. Menapace, D. Ristau, & M. Soileau (Eds.) (p. 923702). Presented at the SPIE Laser Damage, Boulder, Colorado, United States. https://doi.org/10.1117/12.2066909

Cleanliness

MEMS devices and optical components are particularly susceptible to contamination, thus:

  • payload assembly will occur in a class 100,000 or better cleanroom
  • installation and removal operations on an exposed MEMS device will occur under a class 1000 or better flow bench
  • do not use alcohol to clean aluminum mirrors* it reacts with the Al and they have been cleaned at the factory.
  • Only low-out-gassing (per https://outgassing.nasa.gov) lubricants (e.g. Bray-Coat) and adhesives (e.g. 2216 A/B Gray) will be used in the payload
  • guided by NASA STD 8739-1 (WORKMANSHIP STANDARD FOR STAKING AND CONFORMAL COATING OF PRINTED WIRING BOARDS AND ELECTRONIC ASSEMBLIES, https://snebulos.mit.edu/projects/reference/NASA-Generic/NASA-STD-8739-1.pdf) Electrical components will be cleaned as appropriate and conformal coated where possible (e.g. wirebonds cannot be coated)

Cleaning plan

  • Machined and 3D printed parts in view of payload optical components will be ultrasonically cleaned in 4 steps:
    1. wipe down
    2. solvent - acetone or dilute simple green (1 part to 10 parts distilled water) (darthmouth method)
      • Contrex AL (purchased from Fisher Scientific) is preferred as it has much less odor than Simple Green. 1 part to 20 parts distilled water quasi-arbitrarily.
    3. distilled water
    4. isopropyl alcohol
  • do not put flammables in an ultrasonic cleaning tank directly, they must be in a glass container in a water bath

Removing dust from previously cleaned parts

With DM removed the pass the part under the air knife at TBD PSI TBD times or until dust is removed to run air knife:

  1. check that the tube is connected to the nitrogen tank in SSL
  2. open silver top rightmost knob (amount doesn't really matter)
  3. open pressure regulator knob to between 200-500 psi (middle knob, rightmost dial)
  4. open valve to 25 kPa slowly (leftmost valve, left dial) to shut off: close silver rightmost knob, wait for dials to go down to zero, close those valves

Transport

  • Spacecraft and payload transport will be by white glove or hand carry
  • assembled spacecraft will be sealed with low-ESD polyimide (Kapton) tape to prevent contamination during handling and transport outside of cleanrooms.

Humidity and Electrostatic Discharge

The payload is extremely sensitive to the conflicting hazards of electrostatic discharge and high humidity, requiring

  • humidity monitoring of the spacecraft during integration
  • MEMS de operation limited to humidities between 25 %RH and 40 %RH (25-30 %RH preferred)
  • technician payload handling of the powered off payload at $>40$%RH is preferred for ESD hazard reduction.
  • Payload and technician grounding at all times
  • Daily testing of grounding equipment
  • Static dissipative lab coats warn at all times

The above humidity operational requirements can be met with a dry air purge, and low humidity ESD risks during assembly can be mitigated with a benchtop ionizer.