In-Situ Water Vapor Probe for a Robot Arm-Mounted, Compact Water Vapor Analyzer: Preliminary Results

Introduction: This work describes the ongoing development of an instrument package for the in-situ detection and isotopic analysis of water (from ice, icy soils, and hydrated minerals) on future lunar, asteroid, or martian exploration missions. Lessons learned from the Mars Phoenix mission demonstrated that manipulating, sampling, or analyzing icy material is highly complex. This instrument is intended to be mounted on a robotic arm and be brought to the sample (similar to the APXS and Mossbauer instruments on the Mars Exploration Rovers), rather than necessitating expensive and complicated sample handling to bring the sample to the instrument. The analyzer will be capable of in-situ analysis of water-bearing materials on a millimeter scale providing high precision measurements of water abundance and isotopic composition. The high precision isotopic analysis will include D/H, O/O, and O/O. Water is central to NASA’s strategic goals for exploration of the solar system and high precision isotopic analysis, especially of O, provides a key tool in answering fundamental scientific questions about its origin and history. In addition, these measurements can serve as an important component of ISRU operations helping to identify, characterize, understand, and predict the occurrence of volatile deposits. Additionally, this instrument could be utilized in both manned and unmanned missions to a wide range of high priority NASA mission targets including Mars, the Moon, and Near Earth Objects. It also can serve as a key component of an ISRU instrument package providing in-situ prospecting. Our prototype design currently utilizes an “offthe-shelf” instrument (Los Gatos Research, model DTL100 Water Vapor Isotope Analyzer [1-4]) that measures both abundance (ppm) and isotopic (δO, δD) composition by tunable diode laser infrared spectroscopy. This analyzer is coupled to a prototype of a sampling “end effector” that can collect and vaporize water-bearing materials. Preliminary tests of the instrument have consisted of analyzed ice samples for O and H isotopic composition. δO and δD (V-SMOW) variations were approximately ±2‰ and ±4‰, respectively at a 95% confidence level. The long-term goal of this work is to provide a “proof of concept” working prototype where this measurement concept can be fully tested in the laboratory and in the field. We report here initial results from our testing of this instrument prototype where we are examining the effects of gas flow rate, isotope exchange, and different sampling methods for understanding how to acquire high precision isotopes measurements. Instrument Design: A diagram and photo of our in-situ water vapor probe instrument, designed for sampling ice, is shown in figure 1. This device measures ~ 25” high and 14” in diameter and consists of three (24 VDC) gear motors for drilling, raising and lowering the drill stem, and capturing the ice sample. The entire system is contained within a vacuum bell jar and is attached to a vacuum pump and N2 purge as a means of maintaining ambient pressure. The drill tip is tungsten carbide with a fishtail point. The base of the instrument consists of a ice sample “pool” ~500cc volume made of aluminum that allows for water samples to be frozen by means of circulating chilled (-20 to -50°C) ethanol on