University Rover Competition Science Sub-Team
Science Mission
The University Rover Competition is held annually near Hanksville, UT at the Mars Desert Research Station. Each team must design and build a rover compete in four different tasks:
- Science Mission. The rover is required to conduct an in-situ analysis to determine the presence of extinct or extant life at designated sites
- Extreme Retrieval and Delivery. The rover is required to pick up and deliver objects in the field while traversing a wide variety of terrain no further than 1 km from the base station.
- Equipment Servicing. The rover is required to perform operations on an equipment system after traveling up to 0.25 km.
- Autonomous Traversal Mission. The rover is required to autonomously traverse between markers across moderately difficult terrain up to a total distance of 2 km.
The science mission is worth 20% of a team’s overall score. All analyses must be performed by the rover on site, and any liquids used for the analysis must strictly follow a no-spill policy.
Completion of the science task requires knowledge of astrobiology and modern methods used to determine the existence of life. Once the rover has completed an analysis of each site, the team is required to prepare a 10 minute presentation describing the results of each test
System Design
Due to excessive costs of pre-built Raman spectrometers, members of the science sub-team designed and custom-built a Raman spectrometer. Spacing and sizing of lenses and filters required careful calculations to ensure that the instrument would collect meaningful data.
Iterative calculations determined the proper sizing and spacing for each optical element used in the spectrograph assembly. Once proper sizes and spacing were determined, a custom housing unit was designed and 3D printed using a high precision UV-cure resin printer. The design allows minor adjustments to the placement of each optical element to optimize the final footprint of the beam.
The interiors of the spectrometer enclosures are painted black to prevent stray light contamination. The laser coupling subassembly attaches to the laser source. The laser beam passes through an optical band pass filter to ensure a monochromatic excitation signal prior to entering an optical fiber
The signal runs through an excitation fiber to the probe head. The probe uses a 6-around-1 fiber configuration where the light source travels through the central excitation fiber. The six exterior fibers collect the light scattered by the sample surface and direct the retrieved light through a series of optical filters and lenses onto the photodetector. A shroud on the probe head allows the fiber optic cable to maintain a small required stand-off distance from the sample surface and prevents external light from entering the probe.
Methods
While there are a variety of tests that may determine the presence of life, they vary greatly in accuracy, ease of use, and implementation. After researching chemical assays, digital microscopes, and Raman spectroscopy, the team determined to detect life using Raman spectroscopy.
Raman spectroscopy is a vibrational spectroscopy method that measures photons that have undergone Raman scattering, which changes the photons’ energy. The energy change results in a shift in wavelength of the scattered photons, which varies based on the chemical composition of the sample. Because Raman scattering only affects approximately one photon per million, excess light is filtered out while meaningful light is projected onto a Charge Couple Device (CCD) photodetector for analysis.
The data output from the CCD can be displayed as the Raman shift intensity graphed against the wavelength of the shifted light. These graphs are compared to existing databases created from analyzing known materials. The team will compare data output to detect the presence of biomarkers including carotenoids, DNA, RNA, L-amino acids, and lipids. The team will also analyze samples for geobiological features such as banded irons, stromatolites, and carbonaceous materials found in microfossils.
The custom-built Raman spectrometer uses a 532.3 nm green laser. Using a monochromatic light source ensures a clear return signal. Carotenoids have an electronic transition near the 532.3 nm wavelength of the laser, causing the excitation signal to resonate with between 10 and 100 times more intensity than usual. Carotenoids are commonly found in soils and on the surfaces of stones in Utah deserts, making the 532.3 nm laser highly suited to the mission environment.
The versatility of Raman spectroscopy allows rapid analysis of both soil and rock samples. Raman spectroscopy is a non-destructive testing method that avoids the use of chemicals that may violate the competition’s no-spill policy.
Conclusion
The competition rules required that the science sub-team become familiar with the field of astrobilogy and the search for extraterrestrial life. Undertaking this project also familiarized members of the science sub-team with the work currently being done by NASA and ESA to develop a similar Raman spectrometer for use on a future rover mission to Mars.
In order to develop this instrument, members of the science sub-team researched life-detection methodologies, optical engineering, and rapid-prototyping and manufacturing processes. The project also required working with larger interdisciplinary teams for the purposes of integrating the spectrometer with the rover’s power and communications systems.
In its current configuration, the spectrometer is still undergoing electrical integration. In tests, the laser coupling subassembly transmits ≈70% of the power of the laser input into the optical fiber, equivalent to the expected signal loss of greater than once decibel. The spectrograph subassembly light path is verified to produce its intended beam footprint.
Continuation of the project will include use of improved manufacturing methods which will maintain the modularity of the spectrometer while increasing the enclosure’s mechanical strength. Improvements to the driving software will include research into improved signal processing and automated comparison of collected spectra to spectral image databases. The completed spectrometer will teleoperable while the rover is conducting remote missions
Samuel Parastino, Tyler Wallentine, Brandon Kenison marsrover@usu.edu
Special thanks to Spencer Wendel and Blair Martin