An easy and instant method of detection was needed for AF-M315E, a “green” propellant that produces very little vapor. This makes it hard to detect by smell or other active sensors.
Several different techniques were evaluated as possible detection methods for hydroxylammonium nitrate (HAN) and ammonium dinitramide (ADN), two of the primary components of AF-M315E. The technique selected for the detection of these commodities was colorimetric analysis. The reason for choosing this method stems from the nearly nonexistent vapor pressure of the AF-M315E, which made the use of commercial off-the-shelf sensors not feasible.
An indicating absorbent detection system for HAN/AF-M315E was developed that is capable of both detecting (via a distinct color change) the presence of AF-M315E, and helping to contain any spill/leak that occurs. The detection system utilizes an indicator solution containing Methyl Red, which exhibits a distinct color change from red to yellow at a pH range of 4.5 – 6.5. The indicator solution is basified prior to use because AF-M315E has a pH of ~3.65.
The absorbent socks are prepared from commercially available, polystyrene-based chemical absorbent booms that are compatible with a wide range of chemicals (with the exception of hydrofluoric acid). These booms/socks are immersed within the prepared indicator solution, removed, allowed to dry, vacuum sealed (to prevent carbon dioxide absorption), and stored until needed. Additional unaltered booms are included for containment of a leak/spill once detection has occurred. Additionally, indicating chemical wipes are included in the detection system for detection of spills too small for detection using the sorbent socks.
The surfaces of several 3" × 2" stainless steel test panels were wetted using a swatch of microfiber high-performance cleaning cloth saturated with AF-M315E or deionized water, and then wiped using the indicating wipes. When the AF-M315E was wiped, it displayed a vivid color change upon direct exposure to the residual AF-M315E. The deionized water control sample showed no change upon exposure, demonstrating that the indicating wipes are not susceptible to false positives from moisture.
This work was done by Brint Bauer, Robert DeVor, James Captain, Tracy Gibson, and Mary Coan of Kennedy Space Center. For more information, contact the Kennedy Space Center Technology Transfer Office at (321) 867-5033. KSC-13977