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Anti-Fog Solutions for Spacesuit Helmet

Description:

Scope Title:

Anti-Fog Solutions for Spacesuit Helmet

Scope Description:

For the current Extravehicular Mobility Unit (EMU) spacesuit, an astronaut applies an anti-fog solution to the interior of the helmet bubble before each extravehicular activity (EVA). However, the anti-fog solution has been reported to cause eye discomfort during at least seven EMU EVAs when the anti-fog solution contacted the crewmember’s eyes. During STS-100, astronaut Chris Hadfield reported that eye irritation temporarily blinded him during his spacewalk. In addition, the wipe-on anti-fog solution is a consumable that needs to be accounted for and a supply launched for missions. To solve this, the Pressure Garment Subsystem (PGS) team wants the next-generation helmet pressure bubbles to use a permanent anti-fog technology for a solution. Having a permanent anti-fog solution for spacesuit helmets would eliminate eye irritation and the need for additional consumables.

 

During the Constellation spacesuit development program, NASA conducted a trade study on four different permanent anti-fog solutions. The evaluation tested coated samples with the four permanent anti-fog candidates based on Transmission, Haze, Adhesion and Abrasion Resistance, Craze Resistance, Cold Box, Steam, and Human Breath Response tests. 

 

Despite our efforts on Exploration EMU (xEMU) to develop a suitable permanent anti-fog coating on the helmet, the PGS team has had issues with inconsistent application in manufacturing, as well as robustness. It was easily damaged or worn away after only 40 or more hours of manned pressurized time (MPT). It was difficult even during careful cleaning using distilled or deionized (DI) water and a soft, lint-free wipe. In addition, the material used in the xEMU anti-fog coating is being discontinued. There is renewed interest in further investigation into a permanent anti-fog solution such as a coating or other technology for exploration suit helmet bubbles that the xEMU team is interested in pursuing. 

 

 

 Requirements 

  • The anti-fog must be applied to a general purpose polycarbonate bubble.  
  • Geometry is TBD. However, the xEMU bubble is a hemi-ellipsoid 10- by 13-in. polycarbonate bubble and the anti-fog would need to be applied across the curvature.
  • If applicable, the vendor must be able to consistently meet recommended anti-fog coating thickness. 
    • Note: Historically, the required thickness is 6-12 microns, but this will depend on the anti-fog solution chosen.  
  • Must be tolerant to breathing air and 100% oxygen operations environment and able to be manually cleaned.  
  • Testing includes the following:  
    • Steam cycle (simulated breathing). The suggested cycle regiment would be for at least 104 °F temperature steam cycled for 216,000 cycles at 18 cycles per minute. 
      • 104 °F is the high average of exhaled breath temperature.
      • 216,000 cycles is calculated from 18 breaths per minute, 8-hr EVAs, and 25 EVA certification.    
      • Success criteria: No fogging occurring on samples and no evidence of delamination after the test. 
    • Adhesion per ASTM 3359.
    • Cleaning Test
      • Using distilled and DI water and wipe testing for 100 cycles.
  • Must be tolerant to a low-pressure environment (4.3 psia) and meet NASA off-gassing requirements for a confined space.
  • Must be tolerant of pressurization cycles that introduce minor variations of helmet surface area.
  • Maintain optical clarity of the helmet assembly without reducing transmission to less than 70% through visible light wavelengths.  
  • Performance of eliminating condensation while a test subject is in the suit in a relevant thermal vacuum environment for space. 
  • Must pass White Sands Test Facility (WSTF) off-gas testing, specification TBD. 
  • Nice to have: Resistant to isopropyl alcohol (IPA) at any concentration, stericide, or a 50% water/50% dish soap mixture

Expected TRL or TRL Range at completion of the Project: 3 to 5

Primary Technology Taxonomy:

  • Level 1 06 Human Health, Life Support, and Habitation Systems
  • Level 2 06.2 Extravehicular Activity Systems

Desired Deliverables of Phase I and Phase II:

  • Research
  • Prototype

Desired Deliverables Description:

Phase I

  • Completed test plan/report on the following for flat samples: 
    • Steam cycle (simulated breathing). The suggested cycle regiment would be for at least 104 °F temperature steam cycled for 216,000 cycles at 18 cycles per minute. 
      • 104 °F is the high average of exhaled breath temperature.
      • 216,000 cycles is calculated from 18 breaths per minute, 8-hr EVAs, and 25 EVA certification.    
      • Success criteria: No fogging occurring on samples and no evidence of delamination after the test. 
    • Adhesion per ASTM 3359.
    • Cleaning Test
      • Using distilled and DI water and wipe testing for 100 cycles.
  • Consistently able to meet anti-fog thickness requirement from manufacturer along the entire geometry on the helmet assembly.
  • At least five flat samples (no smaller than 1 by 1 in.) of coated polycarbonate. 
  • Monthly status meetings with NASA on progress. 

Phase II

  • Delivered prototype of helmet pressure bubble or equivalent size and shape bubble made of polycarbonate material, coated with permanent anti-fog solution.
  • Completed test plan/report on curve samples or prototype helmet for the following: 
    • Steam cycle (simulated breathing). The suggested cycle regiment would be for at least 104 °F temperature steam cycled for 216,000 cycles at 18 cycles per minute. 
      • 104 °F is the high average of exhaled breath temperature.
      • 216,000 cycles is calculated from 18 breaths per minute, 8-hr EVAs, and 25 EVA certification.    
      • Success criteria: No fogging occurring on samples and no evidence of delamination after the test. 
    • Adhesion per ASTM 3359.
    • Cleaning Test
      • Using distilled and DI water and wipe testing for 100 cycles.
  • NASA WSTF off-gas testing. 

State of the Art and Critical Gaps:

For the current Extravehicular Mobility Unit (EMU) spacesuit, an astronaut applies an anti-fog solution to the interior of the helmet bubble before each EVA. However, the anti-fog solution has been reported to cause eye discomfort during at least seven EMU EVAs when the anti-fog solution contacted the crewmember’s eyes. During STS-100, astronaut Chris Hadfield reported the eye irritation temporarily blinded him during his spacewalk. In addition, the wipe-on anti-fog solution is a consumable that needs to be accounted for and a supply launched for missions.

 

To solve this, the Exploration EMU (xEMU) pressure bubble wants to use a permanent anti-fog coating or other technology that prevents fogging. The EMU program did some work investigating a permanent anti-fog solution, HTAF-308. It failed during qualification due to delamination and flaking after manned testing so was never implemented. During the Constellation spacesuit development program, NASA conducted a trade study on four different permanent anti-fog solutions. The evaluation tested coated samples with the four permanent anti-fog candidates based on Transmission, Haze, Adhesion and Abrasion Resistance, Craze Resistance, Cold Box, Steam, and Human Breath Response tests. The results of that trade study selected HTAF-601 as the primary option. 

 

The HTAF-601 permanent anti-fog solution was tested throughout the xEMU Design, Verification, and Test (DVT) human-in-the-loop (HITL) events. However, major issues have arisen with further HITL testing with the coating. Cleaning the helmet has been a challenge to avoid damaging the permanent anti-fog coating. NASA has completed a set of different methods for cleaning the anti-fog to try to document a preferred method. It was found IPA cannot be used to clean the interior of the helmet because it will strip and delaminate the permanent anti-fog coating. Even with using a very gentle cleaning method of flushing with distilled or DI water and dabbing at facial oils, the permanent anti-fog starts to delaminate consistently after 50 hr of MPT. Finally, the HTAF-601 coating is being discontinued by the vendor. 

 

This subtopic will focus on companies looking at permanent anti-fog solutions that specifically address the issues that the Exploration Pressure Garment System (xPGS) team found with DVT. The hope is an innovative anti-fog solution can be found that is more appropriate and durable for the spacesuit environment. Success for a Phase II completion would be the company's anti-fog solution applied to a flight-like helmet shape of hemi-ellipsoid bubble that has completed sample steam and cleaning cycle testing. This technology could be infused in the current EMU spacesuit or future advanced suits selected by the new program, "Extravehicular Activity and Human Surface Mobility Program Office."

 

Other commercial industries have successfully implemented permanent anti-fog solutions. Ski goggles, motorcycle visors, and fighter pilot helmets are all examples of this technology being implemented. However, most of these solutions are for goggles only, and do not have the requirements of breath cycles. This SBIR will expand the application of this technology. 

Relevance / Science Traceability:

This technology would be applicable to all spacesuit architectures used by the Agency. Also, it is relevant to the new xEMU, International Space Station (ISS), as well as commercial space companies. As the xEMU is being designed, built, integrated, and tested at the Johnson Space Center (JSC), solutions will have a direct infusion path as the xEMU is matured to meet the design and performance goals.

References:

Davis, K. and Kukla, T., "NASA Advanced Space Suit xEMU Development Report – Helmet and Extravehicular Visor Assembly (EVVA)"  ICES-2022-260, 51st International Conference on Environmental Systems, St. Paul, MN, July 2022. 

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