How can you accurately test a space antenna down here on Earth when it has been scaled up to penetrate the subterranean depths of another planet? This was the question faced by SENER in Spain, currently designing a candidate antenna for ESA’s EnVision mission, which will explore Venus from its inner core to outermost cloud layers. To solve it they lifted their prototype skyward with a balloon.
“To develop key technologies for future missions, ESA’s Directorate of Technology, Engineering and Quality often explores multiple approaches,” explains ESA antenna engineer Paul Moseley.
“This includes parallel prototypes for EnVision’s Subsurface Radar Sounder (SRS), which will transmit and receive radio signals to chart the Venusian subsurface. It will achieve this using very low frequencies – 9 Mhz – which in turn means its antenna has to be very large, 16 m across.
“To accurately characterise the performance of SENER’s current prototype it needs to be tested free of any interaction with its environment, but it is simply too big to fit dedicated test facilities such as ESA’s Hertz chamber – which in any case is not equipped to work with such low frequencies.”
The only option left was going outdoors, but the ground would still have interfered with the antenna, distorting the results. So the antenna team decided to suspend the SRS antenna and a full-sized mockup of the EnVision spacecraft from a balloon, lifting it more than 200 m above the ground.
“To further reduce interference from the ground, it was angled to point to the horizon,” adds Paul. “Results from the test campaign show the antenna design is working as expected.”
This testing will help guide the final selection of a source for EnVision’s sounder instrument. The mission, targeting launch in the early 2030s, will also carry spectrometers for atmospheric and surface sounding, a radio science experiment to chart the Venusian gravity field and a NASA-sourced imaging radar.
当一个太空天线被放大以穿透另一个星球的地下深处时，你怎么能准确地测试它呢？这是西班牙的塞纳面临的问题，他目前正在为欧空局的“展望”任务设计一个候选天线，该任务将探索金星从内核到最外层的云层。为了解决这个问题，他们用气球将他们的原型升空。
“为了开发未来任务的关键技术，欧空局的技术、工程和质量理事会经常探索多种方法，”欧空局天线工程师保罗·莫斯利解释道。
“这包括EnVision地下雷达探测仪（SRS）的平行原型，该探测仪将发射和接收无线电信号，以绘制金星地下地形图。它将使用非常低的频率（9 Mhz）来实现这一点，这反过来意味着它的天线必须非常大，直径为16米。
“为了准确描述SENER当前样机的性能，需要在不与环境发生任何相互作用的情况下对其进行测试，但它太大，无法安装专门的测试设施，如欧空局的赫兹室——在任何情况下，它都不具备在如此低的频率下工作的能力。”
剩下的唯一选择是去户外，但地面仍然会干扰天线，从而扭曲结果。因此，天线团队决定将SRS天线和一个全尺寸的EnVision航天器模型悬挂在一个气球上，将其吊离地面200多米。
“为了进一步减少来自地面的干扰，它的角度指向地平线，”保罗补充道。“测试活动的结果表明，天线设计与预期相符。”
该测试将有助于指导EnVision发声器仪器的最终选择。该任务的目标是在20世纪30年代初发射，还将携带用于大气和地面探测的光谱仪、用于绘制金星重力场图的射电科学实验，以及NASA提供的成像雷达。
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