Uncertainty Quantification of Deployable Reflector for NASA Earth science mission

07 Aug 2023

For NASA’s upcoming Earth science mission Investigation of Convective Updrafts (INCUS), three low-earth orbit SmallSats will collect measurements to better understand how air and water vapor move inside tropical storms and thunderstorms, which, in turn, may improve weather and climate models.

Each of the SmallSats are, for performing measurements, equipped with a deployable reflector antenna, since such an antenna may simultaneously provide high antenna gain and low mass and stowage volume. Each of the deployable reflector antennas are fed by an array of seven conventional aluminium feed horns.

Since the instruments, and thus the antennas, will be operating at a relatively high frequency of 35.75 GHz, all manufacturing, mechanical, and thermal tolerances of the antennas are critically important, as even small deviations from the ideal design may deteriorate the antenna performance significantly.

While the behavior of the feed horns is well understood and described by a thermal model, the understanding of the behavior of the deployable reflector surfaces is less mature.

Therefore, engineers at NASA’s Jet Propulsion Laboratory (JPL) resorted to advanced statistical analyses of the deployable reflector model. Their surfaces, to make the antennas stowable and deployable, approximate ideal parabolic shapes by means of a number of surface nodes, whose exact positions may deviate from their ideal position.

Specifically, NASA JPL performed Uncertainty Quantification (UQ) analyses of the node positions using the UQ product in TICRA Tools.

With UQ, the expected antenna performance and confidence intervals are computed for a given antenna model with given uncertainties on parameters of the model.

In this way, NASA JPL’s engineers found that small uncertainties of the node locations in the plane impact the antenna performance substantially less than a vertical (out-of-plane) uncertainty of the location.

Furthermore, the analyses showed that surface node uncertainties mostly impact the sidelobes of the antenna radiation pattern, while the gain and antenna pointing are less impacted.

Picture credit: NASA JPL

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