JUICE-RWI-ANT-CAL

Starting point / motivation

In this project we intend to use numerical models and the experimental method of rheometry to find the true reception properties of the RWI electric field antennas on-board ESA’s JUICE (Jupiter Icy Moons Explorer) mission.

Contents and goals

The JUICE mission is planned to be launched in 2022, with one instrument being the RPWI (Radio and Plasma Wave Investigation) experiment. This instrument will measure the plasma characteristics around Jupiter and its icy moons as well as the electromagnetic wave activity related to Jupiter’s magnetosphere. It contains the RWI (Radio Wave Instrument) antenna system consisting of 3 electric dipoles and a receiver, which will record the radio waves in the frequency range from 80 kHz to 45 MHz.

JUICE will be the first spacecraft in an orbit around Jupiter with a 3-antenna system that allows to measure the intensity, polarization, and incoming direction of the radio waves. However, this unique capability can only be used with a fully calibrated antenna system, and the calibration of the RWI dipoles is the main goal of this project.

Methods

This should be done with the experimental method of rheometry, where a scaled spacecraft model (1:40) is put into an electrolytic tank. It is the first time that an antenna configuration of 3 dipoles (2.5 m tip-to-tip length) mounted on a boom is going to be calibrated by rheometry.

This represents a technological challenge since the length of one dipole arm in the model will only be ~3 cm long, and all 3 orthogonal dipoles have to be oriented in the correct way with respect to the boom.

First numerical simulations in a 1-year precursor project (FFG 844347) had shown that small positional changes at the antenna feeds with dipoles on the boom can lead to large changes in the antenna reception properties. The exact orientation of the 3 orthogonal dipoles is currently being determined in an ESA PRODEX project. 

The rheometry measurements will be complemented with numerical computer simulations, which can describe the antenna reception properties up to 45 MHz, whereas the rheometry result is only valid for the so-called quasistatic frequency case in which the wavelength is larger than the spacecraft dimensions. With the numerical models we can also calculate the influence of the solar panel rotation and the active radar antenna on the passive RWI antennas.

Both methods of antenna calibration with experimental and numerical models have been successfully applied in the past by the Space Research Institute in Graz for various other space missions like Cassini, Stereo, Resonance, Juno, or Solar Orbiter.

Expected results

A successful completion of this 15-months project, which is strongly supported by the RPWI Principal Investigator, would again show the leadership of the Austrian Space Research Institute in the calibration of radio antennas.

This would be for the benefit of the first European-led space mission to an outer planet in which Austria should participate as an ESA member. The total costs of the project are ~170 k€, from which we request ~170 k€ to be funded by FFG (100% support ratio).

Coordinator

Austrian Academy of Sciences

Austrian Academy of Sciences
DI Dr. Georg Fischer
Schmiedlstraße 6
A-8042 Graz