The Attitude Lab would provide the nadir direction of the gondola during the float phase. It is based on the use of commercial photodiodes which would provide a measurement of the infrared radiation coming from its Field of View with the Earth. Therefore, minimizing the interference with other elements on board the gondola structure is extremely important. This nadir sensor will be placed in the Downward Environmental Lab and will also carry two temperature sensors for correcting the measurements after the flight.

The design for the Nadir sensor is mainly restricted by the proposed functional range, a 10° semi angle Field of View for all the photodiodes, a reduced envelope close to a 50 x 50 x 50 mm3 cube and the manufacturing method based on COTS. All the designed parts are manufactured via 3D-printing at the IDR/UPM facilities with Ultem The sensor carries four photodiodes, encapsulated in an adapter as shown in
the following figure, designed to restrict their Field of View to meet the requirements, reducing the interferences with the gondola or other experiments.

Photodiode and adapter for the Nadir sensor.

The main body of the sensor is divided into three different sections, as enumerated in follofing figure. Section 1 and 2 are fixated together with four M3 screws and provide the support for the photodiodes’ adapters, which are kept in place by compression. To estimate the photodiodes’ temperature two PT1000 RTDs are attached to the bottom of two photodiodes aligned in the same axis. Sections 2 and 3 are adhesive bonded. Between these two sections the 15-pin connector is held in place with a custom adapter that is adhesive bonded to the sensor’s main body.

Section 3 is fixated with four M3 screws to the Bottom Section of the sensor. This component allows the whole structure to be fixated in three points (not included within the sensor’s envelope) to the Attitude Lab support plate.

Nadir sensor design and its components.