A sensor element that consists of a thermally resistive layer made of nand p-type semiconductor elements amplifies the temperature gradient in the resistive layer that results from heat flow through the sensor. The thermoelectric array provides greater accuracy and sensitivity over a traditional thermopile arrangement for heat flux measurement. The thermoelectric sensor array is an adaptation of technology developed for generating electricity in radioisotope thermoelectric generators that operate with internal temperatures in excess of those at Venus. The technology is used in a different manner in that, instead of generating electrical power, it measures heat flow using a temperature differential output and a voltage output.
In operation, the sensor is deployed on a boom or arm that is attached to a Venus lander. During descent through the atmosphere, the sensor is exposed to the Venus environment because it resides on the exterior of the vehicle. At deployment, the sensor is likely to be at thermal equilibrium with the local environment. After the sensor contacts the ground surface, a current is passed through the thermoelectric elements of the sensor. This provides a cooling of the copper plate at the bottom of the sensor. The plate is heated by the flux coming from the Venus surface. The transient response of the sensor provides a direct correlated measurement of the heat flux at the surface. It is not necessary for the sensor to come back to equilibrium with the environment to make a heat flux measurement. This transient measurement technique allows for several heat flux measurements to be made with the sensor while the lander is operating.
This work was done by Michael T. Pauken, Suzanne E. Smrekar, Jean-Pierre Fleurial, and Jordan R. Chase of Caltech; Tim Knowles of Energy Science Laboratories; and Paul Morgan of Colorado Geological Survey for NASA’s Jet Propulsion Laboratory. NPO-49434