The objective of the GAP-GC-TDLAS Laser spectrometer was to detect water vapour isotopes (H216O, H218O, H217O, and HDO), carbon dioxide isotopes (CO2, 13CO2, 16O12C18O, 16O12C17O), as well as methane (CH4).
The TDLAS was based on diode-laser absorption spectrometry. The laser’s emission wavelength was set close to a target molecule’s rotation-vibration transition by adjusting the laser’s temperature. The laser beam travelled through the gas sample (for approximately 1 metre in the case of Phobos) and was partially absorbed by the molecules in the gas sample, providing an absorption spectrum which was recorded.
The TDLAS used 4 laser diodes with 4 different wavelengths:
- one diode at 2.04 µm for CO2 isotopes,
- one diode at 2.64 µm for H2O isotopes,
- one diode at 2.68 µm for H2O and CO2,
- one diode at 1.53 µm for acetylene (C2H2).
The following steps were under the responsibility of the GSMA from the University of Reims:
- designing, in collaboration with IKI, the TDLAS instrument (building on the GSMA’s experience in laser development for high-altitude balloons);
- determining, delivering, and describing various components (laser diodes, optical instruments (separators, micro-lenses), sensors, electrical components);
- developing laboratory testing methods to perform operational tests on the instrument prototype;
- taking part in assessing different TDLAS models and determining their potential (under IKI supervision);
- developing inversion model software for data processing.
Four GAP-GC-TDLAS models were built:
- one laboratory model (LM) delivered to the GSMA in April 2009;
- one qualification model (QM), ready in December 2008;
- two flight models:
- FM1, ready in January 2009;
- FM2, ready in July 2009.