Titan Lake and Shore Sampler

NASA’s Jet Propulsion Laboratory, Pasadena, California

A lake and shore sampling and sample distribution system was developed for a Titan lake environment (93.7 K, in liquid hydrocarbons). The Titan Lake and Shore Sampler (TLASS) would enable the chemical analysis of hydrocarbon lake samples via a Dual Rectilinear Ion and Orbitrap Mass Spectrometer and Nuclear Magnetic Resonance (NMR) Spectrometry.

Cross section of the CAD model of the cryogenic actuator along with an assembly blow up.

In the operations concept for this system, the outer surface of the spacecraft is in contact with the methane and ethane of the lake. Any significant heating from the spacecraft will produce boiling. In addition, pulling the lake liquid into the sample handling system must be done under thermal control to prevent flash evaporation of the sample. Heat flow from the outer surface and the sampling chamber surface must be limited to ensure that the temperature at the spacecraft surface remains below the vapor pressure of methane. The power dissipated by the valving sample distribution system must be small and conducted away from the sample inlet.

A system was built to demonstrate the required functionality of a potential Titan sampling system for sample distribution to three separate instruments. A vacuum manifold supplies the vacuum to the inlet ports of each instrument. A solid sampler that is to be developed utilizes a narrow pneumatic penetrator that samples the solid and returns the sample to the spacecraft where it is melted under controlled conditions. The sample outlet of the solid sampler is connected to the inlet of the liquid sampler allowing for a single solid sample to be delivered by melting to the liquid sampler and sample handling system design. A variety of thermal problems need to be addressed when sampling from a cryogenic lake. The first is the heat flow from the spacecraft to the local fluid.

The best candidate actuator material for this application, based on mass, power, and reliability, were the new single-crystal piezoelectric materials that have been developed for cryogenic applications. Since the origin of high electromechanical properties of relaxor-PT single crystals is due to the polarization rotation effect (i.e., intrinsic contributions), the property degradation at cryogenic temperatures is much lower than in PZT (lead zirconate titanate) ceramics, making them promising candidates for cryogenic actuators from the perspective of stroke and power loss in the actuator when activated.

The novelty is the use of cryogenic valving to implement a sampler system that can operate at cryogenic temperatures. The potential mission target of Titan has methane and ethane lakes that are in thermal equilibrium with the atmosphere and surface. The vapor pressures of methane and ethane are important for the effective design of an ambient phase sampler. The surface pressure and temperature of Titan is 1.47 atmospheres and 93.7 K. The boiling temperature (when the vapor pressure equals the ambient pressure) of the methane and ethane would occur at 110 K and 190 K, respectively. This means that thermal control of the sampling system is critical for the controlled sampling, and the heating of each of the liquids must be small, to be accounted for by the heat capacity of the methane and thermal conductivity away from the spacecraft. The cryogenic valves developed for this instrument will allow for the sampling and interrogation by critical instrumentation to determine the complex physical chemistry found on the surface of Titan or other cryogenic worlds.

This work was done by Stewart Sherrit, Eric A. Kulczycki, and Wayne F. Zimmerman of Caltech; Nobuyuki Takano of the California Polytechnic Institute; and Louisa Avellar of UC Berkeley for NASA’s Jet Propulsion Laboratory. NPO-49343