In March 2000, NASA Human Exploration and Development of Space (HEDS) independent assessment report JS 0024, “Adequacy of Intravehicular Detection and Removal of Hypergolic Propellant Contamination Following Extravehicular Activity,” documented a need to detect and remove hypergolic propellant contaminants in the airlock after an extravehicular activity (EVA). Contamination may occur when an EVA astronaut brings dangerous levels of hypergolic propellant into the airlock. When the airlock is pressurized, the contaminants may be released in the airlock chamber, thus potentially contaminating the airlock and the breathing environment of the Space Station and Shuttle and causing a critical risk to crew and vehicle safety. In 1995, the American Council of Governmental and Industrial Hygienists (ACGIH) adopted a more stringent Threshold Limit Value (TLV) of 8-hour time-weighted average at 10 parts per billion (ppb). Because there is no sensor system that adequately provides real-time, early warning of the hazardous conditions in the space and airlock environment, the EVA crewmember must undergo rigorous, time-consuming procedures to remove any contaminants. Such activities include scrubbing the space suit with a brush and baking off any remaining contaminants in the sun prior to entering the airlock. It is not desirable to repressurize the airlock to purge contaminants because of a limited supply of oxygen. As a result, the report indicated a need to develop a small, real-time, lightweight, and power-efficient sensor to detect very low levels of contaminants in the airlock environment. An ion mobility spectrometry sensor was developed for monitoring hypergolic fuel in the airlock. However, because of its high maintenance cost, downtime, and inability to detect 10 ppb, the sensor is no longer in use. Currently, several detectors are in development in hope of meeting the safety requirement. These instruments use paper tape, mass spectrometer, or electronic nose technologies. It can cost millions of dollars to develop, implement, operate, and maintain an instrument. None of the instruments can remove the contaminants on the space suit. An instrument may be successfully developed to monitor the airlock; however, it will not work in space since the hypergolic fuels are in liquid form and cannot be pumped into the instrument for detection.

Our approach was to develop a wipe that can effectively detect and remove hypergolic propellants before the astronauts enter the airlock. The method is to coat an absorbing wipe with an indicator that will change color when exposed to hypergolic fuel. In addition, it will remove hypergolic fuel from the space suit.

A market search indicated a microfiber material made of 70-percent polyester and 30-percent nylon that can absorb liquids 8 times its weight. After subjecting the material to ignition and reactivity tests with hydrazine and monomethylhydrazine, the material was deemed safe for use. The ignition test consisted of measuring temperature change when a 2-inch square of material is in contact with 0.5 milliliter (mL) of propellants for 10 minutes. The reactivity test consisted of soaking a 4-inch square of material with 1 mL of propellants for 10 minutes. A 10-percent aqueous solution of the universal indicator was prepared. This solution was also deemed safe. Test wipes consisted of 1-inch squares of the microfiber material. They were first submerged in deionized water and ultrasonically washed for 1 hour with 3 changes of deionized water. They were block-dried and then air-dried. Then 0.5 mL of the 10-percent indicator was added to the dried squares. The wipes were ready to use. To test the function of the wipes, 0.5 mL of hydrazine was added to a wipe, and an instant change of color to bright green was observed. The tests also consisted of wiping a piece of clean space suit material with a few drops of hydrazine on it and observing color change and absorption. To determine how much hypergolic fuel could be absorbed, drops of hydrazine were added to the wipe. It was found that a 1-inch-square wipe could absorb 2.5 mL of liquid. The reacted wipes were stored in plastic bags.

The universal indicator consisted of a combination of pH indicators, each of which changes color at a certain pH value. For example, bromophenyl blue changes from yellow to blue at pH 3.0 to 4.6 and phenolphthalein changes from clear to pink at pH 8.2 to 10. Since the universal indicator is a combination of pH indicators, it shows a distinct color for each pH value. Hypergolic fuels hydrazine and monomethylhydrazine are basic (pH greater than 7); the universal indicator will show a green/blue color.

Once the wipes are doped with universal indicator and stored in a plastic bag, there are ready to use. There is no maintenance required. The operation of the wipes is very easy – just wipe the surface of the space suit and observe a color change. This can be done before the astronauts return to the airlock. If there is no color change, there is no exposure of liquid hypergolic propellants. The used wipes can be stored in a sealed plastic bag for disposal at a later date. Results are shown in the photo.

The application of a wipe to detect and remove contamination of the space suit can be extended to commercial applications on the ground, such as developing color-indicating protective garments and color-indicating wipes.

Contact: R.C. Young (Rebecca.Young-1@ksc.nasa.gov), YA-C3, (321) 867-8765