Thermal and Evolved-Gas Analyzer (TEGA)

See also TEGA file naming

The TEGA instrument, one of seven instruments aboard the 2007 Phoenix Mars Lander, is a thermal and evolved-gas analyzer. TEGA is designed to analyze ~50 mg of fine grained soil or rock fragments that are loaded into ovens via a funnel. It consists of four basic components: a soil delivery system, an oven/calorimeter, a gas storage and handling system, and an evolved-gas analyzer (EGA).

TEGA will analyze eight soil/rock samples. The samples are acquired from the Martian surface by the Phoenix Robotic Arm. The arm scoops the soil sample up and deposits it in the TEGA soil delivery system. The TEGA soil delivery system is made up of a door release mechanism, a screen, a vibrating solenoid, a tri-bladed soil impeller, and the trough/funnel which delivers soil to the male oven half. A 1 mm grid screen acts to filter out particles too large for the oven. The vibrations of the solenoid are imparted to the entire thermal analyzer (TA) chassis to sift soil through the screen, as well as assist gravity in the movement of the soil down the trough to the funnel area of the TA, which fills the male oven half. A detector and LED pair is located across the collar of the funnel just above the male oven half. The LED/detector pair (LEDEDR) is used to indicate when the oven is filled.

TEGA is built with eight, single-use thermal analyzer (TA) cells, each of which has its own oven and sample receiving funnel. The TEGA ovens are very small. The inside dimensions are about 2.4 mm diameter and 8 mm long. The male half, which receives the sample material via a funnel, is inserted into the female half, which contains heater and temperature sensors. The TA cells are used to collect calorimetric data, i.e. temperatures and heat flows associated with thermal transitions in a material, on the sample. These data are collected to characterize the thermodynamic and chemical properties of the sample material. Calorimetric data (SCEDR) is obtained by carefully measuring the power applied to the oven to achieve a desired temperature during a programmed temperature ramp.

During the programmed temperature ramp a stream of N2 gas is run over the sample as it is heated from ambient temperatures to about 1000°C. The gas supply serves two purposes; one is to provide a carrier gas that moves the gases evolved from the sample material in the oven to the inlet of the EGA, and the other is to provide an on-surface known composition calibration gas. The gas storage and handling system consists of two tanks, valves to control and distribute the gasses to the eight TA modules and the EGA, and the associated plumbing. Various engineering readings associated with the gas will be recorded in the engineering data products (ENGEDR).

As a sample is heated, various gases are evolved depending on the nature of the sample. The evolved gas is passed through a manifold to the EGA. The EGA is a magnetic-sector mass spectrometer, which can determine both the quantity of the evolved gas and its isotopic composition (EGAEDR, EGHEDR). The detection limit of the EGA is 10 parts per billion. The EGA is synchronized to the temperature of the oven, so the composition of the gases can be correlated to their temperature of evolution. In Mass Hopping mode the EGA only scans certain selected masses. After the top of one mass peak is sampled, the instrument hops to another mass, skipping over insignificant peaks and the empty space between peaks.

TEGA is controlled by flight software that runs on the dedicated TEGA microprocessor. The flight software issues commands to the instrument, and collects housekeeping and science data (SCEDR, EGAEDR, EGHEDR, ENGEDR, MSGEDR, LEDEDR). The TEGA flight software reports TEGA specific information to the Lander command and data handling system. TEGA information collected by the Lander is then returned to Earth via the Deep Space Network.

Source: TEGA EDR SIS