Deployment Mechanisms for Lunar Antenna

Sky radio emission below 10 MHz is inaccessible from the ground due to the absorption and scattering in the ionosphere. To explore this region of the EM-spectrum, a space based radio telescope would be required. unlike spatially distributed array, a single Tripole antenna can measure the 3D electric field, and protect the desired signals from interferences. Tripole antenna can also be used to estimate the directions of arrival (DOA) of multiple incident signals which makes it suitable as a candidate antenna for space based observing at low frequency. A tripole antenna consists of three co-centered orthogonal dipoles. Deployment mechanisms for such an antenna is introduced.

Folded Strips

The design is for simple metallic strips with rectangular cross-section, bent along the side of the bottom. The advantage of this design is the low mass due to the absence of any complicated mechanical system. The energy needed for deployment is only contained in the elastic energy of  these folded strips. However the deployment needs to be controlled and  should make sure that releasing the deployment won’t cause any damage to the other equipments of the lander. The releasing mechanism can be a Nylon wire/Thermal knife. Amongst the drawbacks of this design is relatively uncontrollable and unpredictable kinetic energy dissipated during the deployment as it could cause a mass surplus in the boom’s structure. Therefore the boom should be strengthened to make sure it can bear theses transitional moves.

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Folded strips model for a tripole antenna and a view of connection between antenna arms

Umbrella

Like an umbrella, in this model each antenna arm is divided to two or more sections where the joint pieces release the folded arms using the springs. This design is sensitive to the temperature variations and other causes of the deformation of structure. Besides the reliability, the joint parts may affect the antenna electromagnetic pattern.

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Tape‐measure Housing

The design consists of antenna arms to be formed like a metallic tape- measure with a very thin (~ 0.1mm) U‐cross section that is wound around a reel.  Antenna’s  deployment  is  driven  via  the hollow  axles using bearings. Similar to folded strips, this mechanism doesn’t need energy for the deployment; the potential elastic energy of the pre-stressed antenna  is sufficient for antenna deployment with high reliability.  It is also the most compact design where a 2x4x4 cm box provides space for a rolled antenna of 1.25 m . Another advantage of this mechanism is that the box provided for releasing system can be used for electronics parts such as LNAs which is connected between dipole arms. In the meantime each arm should be conducted via multiple bearings through the axles to eject the antenna in the right position.

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Plots of tape-measure housing deployment model for a tripole antenna with 6 arms

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A prototype model for testing the mechanism

projects/antenna_deployment_mechanisms.txt · Last modified: 2017/07/27 15:56 (external edit)
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