Development of Laser Communications for Tunable Laser Broadband Spectrometer Pertaining to Small-Satellite Tomography of Planetary Atmosphere

This research aims to develop a novel scientific instrument for atmospheric measurement using tunable lasers designed specifically for small satellites in formation flight, called TLSS (Tunable Laser for Small-satellite Systems). TLSS will measure the isotope ratio of key chemical species on the planetary scale, providing insight to the evolution of atmospheres and establishing habitable zones in both our worlds and those of other solar systems. The isotopic shifts of gases in the Martian atmosphere have been measured with unprecedented accuracy through the NASA Curiosity rover. The Sample Analysis at Mars (SAM) instrument has determined the abundance of methane on Mars. TLSS provides further advancement of SAM by enabling planetary-scale application of tunable lasers in measuring isotopes by physically separating the light emission(s) and detecting sensor(s), enabling free-space measurements, while simultaneously capable of detecting ultra-fine spectral lines and wide-band spectrums. TLSS is characterized by, at the minimum, a pair of small satellites in formation flight, where one hosts the emitter while the other the detector. SAM achieves its required signal-to-noise ratio with the Herriott cell, increasing its integration path for in-situ measurements of a collected sample. In contrast, TLSS’s integration length is controlled by the separation of the satellites, making it capable of planetary-scale measurements. Our team envisions Venus as an excellent first mission for TLSS, where in-situ measurements techniques such as SAM is unlikely to be viable due to the harsh environment of high-temperature, high-pressure, and acidic atmosphere for a roving or low-flying vehicle. Unlike other methods of spectrometry that can reliably detect gases, TLSS’s collected data of isotopes will provide insight to the formation, climate change, and geological activity of a planetary body. The focus of present TLSS development effort is on the requisite real-time communication from the emitter to the detector on its spatial, temporal, frequency, intensity, and waveform information. Three signals have been sent from microcontrollers, PIC18F47K42, using asynchronistic serial out to a blue, red, and green LED at 20 bauds. The signals were received by Ocean Optics spectrometer USB-4000. The output serial signal and the detected signal of all three-wavelengths matched, ensuring the accuracy of this method. This process demonstrates reading out a message from optical communication methods that will be implemented into the TLSS. Replacing the LED serial communication, laser diodes will be used to increase data bandwidth with its narrow linewidth. The expected spectrometer for TLSS satellite technology demonstration is the StellarNet BLK-C-SR, with holographic grating range of 200-1080nm and detector integration time of 1ms to 65s, and the DS-InGaAs-1024, 1024 element InGaAs photo diode array over range of 1.0-1.7um; the communication baud rates using these detectors will be significantly faster (~1000x) as these spectrometers have the capability to poll measurements from a single pixel.