Raman Spectrograph for Ocean Worlds (RSO): New Capabilities for NASA's Europa Lander, 15-R8834

Background

Jupiter’s moon Europa has an icy shell covering a large global liquid water ocean with likely hydrothermal vents at the ocean floor. This environment may be conducive to the formation of life. The search for biological signatures on Europa requires a lander mission payload with exquisite capabilities for spectroscopic analysis of ice sample composition in order to characterize the biological potential. The Deep Ultraviolet (Deep-UV) Raman spectroscopy technique is well suited for key measurements of biologically relevant species, including organics, isotopes, amino acids, and other complex molecules. However, Raman spectrograph instruments customized for planetary science investigations are new, making this area of study well suited for rapid growth and innovations.

Approach

Figure 1: Functional prototype of an iCERS cavity operating at SwRI.

SwRI is developing a high-sensitivity Deep-UV + visible dual-laser Raman system for spaceflight in order to address astrobiological science goals applicable to ocean worlds such as Europa. Our Raman Spectrograph for Ocean worlds (RSO) instrument design utilizes a technique called integrating Cavity-Enhanced Raman Spectroscopy (iCERS), which was developed by collaborators at Texas A&M University and advanced in a previous IR&D program unrelated to space science. This iCERS approach has already demonstrated a few orders of magnitude enhancement of Raman-signal and femtomolar-level-measurement sensitivity, making it well suited to searches for trace biosignatures in icy samples.

Project tasks emphasized reducing key technical risks for the instrument development:

• Baseline iCERS Deep-UV measurements for astrobiology sample types.
• Beamline tests at MIT to characterize
  • fluorescence from MeV electrons and gammas.
  • color center production rate/reflectance degradation vs. dose rate.
• Analytical modeling of radiation effects, fluorescence yield, etc. for both partially sintered and compressed powder options for the cavity material and design.
• Detector radiation characterization within landed spacecraft vault.
• Full measurement background subtraction characterization.
• Additional solid-model, thermal-design, and mechanisms tasks.
• Vibe-test a cavity.

Accomplishments

Several prototype integrating cavities were used to measure ice sample mixtures with amino acids (glycine), deuterated water ice, table salt (NaCl), Epsom salt (MgSO4), and methanol ice to demonstrate the capability of our initial bench top device to deliver science measurements (even after irradiation). Radiation tests of custom integrating cavities built at SwRI, fiber optic cables, and candidate laser diodes were conducted in a MeV electron beamline at MIT, with radiation levels representative of the Europa environment. No significant performance degradation was detected, and no background signal noise is expected to result from this source as a result of the intense radiation environment when measuring samples on Europa’s surface. Detailed designs for optical, mechanical, electrical, and laser subsystems were developed as planned prior to submitting proposals in response to NASA’s Instrument Concepts for Europa Exploration 2 and Development and Advancement of Lunar Instrumentation opportunities (Figure 2). The final vibration test of the integrating-cavity prototype was successful, elevating its technical readiness to component level 6 as planned. Our expectation is that the further development and flight of SwRI’s enhanced RSO system enables new investigations where exquisite compositional measurements of trace minerals are required, which includes not only the most astrobiologically interesting ocean world environments in the Solar System such as Europa, but the Moon and other planetary bodies as well.