Background
The keys to understanding the origin and evolution of our solar system lay hidden beneath the surface of the myriad planets, satellites, and primitive bodies that orbit our sun. The volatile content buried therein stores evidence of the primordial events that shaped our home and records chemical and physical interactions that continue to this very day. Identifying and characterizing the subsurface volatile contents (water, organics, noble gases, and others) will help to answer priority questions identified in the Planetary Science Decadal Survey.Conventional methods for collecting and analyzing surface samples at solar system bodies are costly, complicated, and invasive. Typically, they involve drilling and/or scooping to collect materials, which are then delivered to an instrument suite for analysis. Such mechanical action requires a significant amount of force and exposes subsurface samples to the ambient environment. This exposure has the potential to degrade the inherent volatile content and reduce the scientific value of the sample. On bodies with tenuous atmospheres, exposing the substrata could lead to immediate desorption, sublimation, or modification of extant volatile resources, as witnessed on Mars when the Phoenix lander observed the rapid sublimation of freshly uncovered icy material.
Approach
VESPAIO provides a means to examine the volatile record without destroying or significantly altering the source material through a synergistic combination of established technologies; ultrasonic drilling, stimulated desorption, gas sampling, and mass spectrometry. During this project we completed the design, fabrication, and ultra-high vacuum testing of a prototype gas sampling ultrasonic drill probe. The resulting device is comprised of three distinct sections; transfer tube, gas diffuser, and probe head. For testing the prototype sits in a vacuum chamber mounted atop the Lunar Advanced Vacuum Apparatus (LAVA) which houses a 20in. graduated cylinder filled with lunar regolith simulant. The VESPAIO and LAVA Vacuum environments are effectively isolated from each other and have different pumping systems.
During experimental operations the probe is allowed to slowly fall under its own effective mass into the regolith simulant. Ultrasonic chips in the probe head are driven through a range of frequencies exciting the conical tip to vibrate, similar to a Langevin Transducer. The vibrating tip stimulates volatile desorption in the regolith. Identical RGA’s mounted to both VESPAIO and LAVA allow comparison of volatile gases that travel through the prototype and those that escape. Probe position, temperature, and frequency are recorded along with mass spectra from each chamber. Driving the ultrasonic chips beyond resonance causes excessive heating which allows thermal desorption testing.
Accomplishments
This project was designed in a phased approach to meet four key research objectives:
Demonstrate a fully operational prototype at TRL 4-5,
Achieve ultrasonic penetration of lunar simulant in a UHV environment,
Observe thermally and mechanically stimulated desorption of volatile gases trapped beneath the surface of a simulated lunar environment, and
Directly sample and characterize the desorbed volatile gas content at depth in a simulated lunar environment.
Objectives 1, 3, and 4 were successfully completed. Objective 2 could not be completed due to an unseen obstruction in the chamber.