In-situ spectral calibration module for an earth observation satellite

Abstract

With climate change being a prime source of concern around the world, air pollution is a topic that requires special attention. Therefore, it is of utmost importance to track and measure the emissions in our environment for detecting the sources and understating the climate change so as to figure out possible solutions. Despite ongoing development, the current LEO and GEO satellite instruments have a long prolonged global survey, revealing the pollution trends at a broad scale, but there is still a lack of high-resolution data to pinpoint pollution sources.

For this, John Hopkins University (Applied physics lab) and NASA are now developing a new earth atmospheric monitoring mission called Compact Hyperspectral Air Pollution Sensor (CHAPS) to address it at a local scale. Presently, TNO is carrying out the design study for this system by employing both freeform optics and additive manufactured mechanics. The mission objective is to perform targeted local measurements of the atmosphere on a daily basis by providing high spatial and temporal resolution possible in UV-VIS wavelength range.

In order to characterize, quantify, and monitor emissions from urban areas, power plants, and other anthropogenic activities, it is important to collect accurate and precise data and calibrate the optical instrument. But the data often received from the sensor is not reliable due to the operational and the non-operational conditions leading to cross-sensitivity, change in the trajectory, and optomechanical errors. For this, an on-board calibration system is developed to perform continuous calibration of the science product, that is compatible with both the instrument and the satellite platform and is robust to the variable operating conditions. This requires a stable system that achieves a good performance that is insensitive to thermal and mechanical disturbances, in order to meet the strict specifications.

As opposed to conventional methods, additive manufacturing, enables new possibilities for developing Optomechanical structures because of the layer-wise manufacturing technique. This manufacturing process is widely touted as a foundation for the next industrial revolution as it offers profound advantages like shorter lead time, lower wastage of materials, and higher geometric complexity that can be useful for multi-functional and multi-material structures. It can also facilitate good strength, significant mass reduction, and better dimensional homogeneity and stability. At the same time, additive manufacturing is not an easy process and requires new design strategies and solutions for overcoming the existing constraints.

The prime research objective is to investigate the optomechanical design of the spectral calibration module applying a kinematic approach. The second research objective is to investigate design and the potential improvements when applying additive manufacturing. The present case study demonstrates and evaluates the preliminary phase of the calibration module design study, thus providing the key ingredients for the realisation of the full system.