1996: Two-channel solar spectrometer. Part of the Russian Mars-96 mission.
The Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars instrument is a two-channel solar spectrometer. It was placed on the Russian Mars-96 orbiter. The mission was launched in November 1996. The mission failed half an hour after launch due to a rocket problem. The instrument contained a UV-visible channel (250 – 650 nm) and an IR channel (1.8 – 4.8 micron).
Its scientific objectives were the determination of vertical profiles of ozone, water vapor, carbon monoxide, aerosols and temperature in the lower and middle atmosphere of Mars.
Launch: November 16, 1996
SPICAM-SThe goal of SPICAM-S was to characterize the atmosphere of Mars, especially the vertical content of the major components (CO2, H2O, O3, O2, CO, dust and aerosols) and their variation intime and geographical location. Also the registration of temperature and density profiles is a major objective.
Spectroscopy is the science that studies the characteristics and composition of a light source based on its spectrum. If the spectral contents of a light source (e.g. the Sun) is modified by absorption by chemical elements, this is called absorption spectroscopy.
SPICAM-S spare flight model (BIRA-IASB museum)
During the short periods of time that the Sun, the atmosphere of Mars and the spacecraft are in one line, the solar light, that has interacted with the atmosphere, carries information about the composition of the atmosphere at that specific time (season, local time) and location (latitude, longitude, altitude) towards the instrument.
SPICAM-S is an optical spectrometer, sensitive in the UV, visible and infrared wavelength ranges of the solar spectrum. It is composed of two separate channels: the UV-VIS channel (200 – 750 nm) and the infrared channel (1.8 to 5 µm). Each channel consists of a spectrometer preceded by a focusing optical system and followed by a detection system.
MARS-96 spacecraft
Since SPICAM-S uses the Sun as light source, the experiment has to be pointed towards the Sun and track it. The spacecraft itself assures a pointing of the SPICAM-S aperture towards the Sun with a precision of ±1°. Therefore the dedicated suntracker of the instrument has only to perform smaller corrections. The SPICAM-S suntracker is built around a central mirror situated underneath the aperture of the instrument and reflecting the incident solar light towards the entrances of the spectrometer channels, and towards a Position Sensitive device (PSD). This PSD detects the position of the Sun and couples back this information to the motors driving the mirror.
SPICAM-S shutter system (BIRA-IASB museum)
The instrument can be shut off by a shutter mechanism. It is built to perform multiple openings and closings. Nevertheless it is equipped also with an irreversible pyrotechnical emergency opening function.
SPICAM-S contains also a control camera, making images in low resolution of the solar disk, giving information about the shape of the observed solar disk and the point of the Sun that is actually tracked.
SPICAM-S solar tracker (BIRA-IASB museum)
The four units (two spectrometers, shutter/suntracker and control camera) are driven by four independent electronic units, each with its own microprocessor or microcontroller.
Observation occasions with the SPICAM-S instrument are rather rare. Seen from the instrument there will be one sunset and one sunrise per orbit of the spacecraft. Only during these two short periods SPICAM-S will be capable of doing its measurements.
