Mars Volatiles and Climate Surveyor (MVACS)

Tunable Diode Laser Spectrometer

R.D. May (PI) and D. Paige

MVACS is the lander payload for the Mars ’98 Surveyor mission to Mars. The integrated payload consists of four primary instruments: a robotic arm equipped with a camera, a surface stereo imager, a thermal and evolved gas analyzer (TEGA), and a suite of sensors for measuring pressure, temperature, and winds (MET). The prime landing site is near 75° S in Martian late southern spring, targeted to allow studies of the geologically-interesting south polar layered terrain.

Two tunable diode laser (TDL) spectrometers are integrated into the MVACS payload. These were designed and built at JPL, and represent the first space-qualified TDL spectrometers. The single-frequency, distributed feedback (DFB) lasers were also fabricated at JPL and qualified for this mission. Both spectrometers are equipped with two TDLs for measurements of isotopic CO₂ (2.04 m m) and H₂O (1.37 m m) using second harmonic detection and multipass Herriott-type absorption cells. One spectrometer is located on the MET mast for measurements in the free atmosphere approximately 1m above the lander deck. The optical pathlength is 10m defined by 38 traversals of the output laser beams between a pair of spherical mirrors. The second spectrometer is an analyzer for the TEGA instrument and monitors CO₂ and H₂O evolved from heated soil samples. Its optical pathlength is 1m acheived by multipassing the laser beams 18 times in a small Herriott cell located in a temperature-controlled housing (see picture). Shown below is a laboratory spectrum in a MET simulation chamber showing the various isotopes of CO₂ that can be monitored at 2.05 m m. The spectrum is a single scan recorded using flight electronics.

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