MRI: Development of A Real Time Antenna Metrology System for the Large Millimeter Telescope

在毫米波段对宇宙的观测解决了一系列广泛的科学问题。直径50米的大毫米望远镜阿方索·塞拉诺(LMT)是这项工作的关键。LMT是由墨西哥国和马萨诸塞大学阿默斯特分校合作建立的。它是世界上同类望远镜中最大的，为美国的天文学家提供了重要的研究工具。像LMT这样的超大型天线必须仔细对准才能以最佳状态运行。一个主要的限制是望远镜的内部对准在加热和冷却时发生变化。该项目将建立一个系统来测量天线表面的形状和反射镜的内部对准，从而允许LMT调整和保持其对准。在白天，当结构的太阳能加热引起最大偏差时，这种改善将是最显著的。该项目广泛利用学生和年轻的LMT工作人员来培训下一代科学家和工程师。与LMT的研究将美国和墨西哥的天文学家联系在一起，鼓励两国之间的科学合作。像LMT这样的大型单碟式射电望远镜的最终性能受到其对天线结构中的温度梯度的响应的限制，这些温度梯度导致主反射面变形，导致天线增益的损失。这些变形还会改变次镜和主镜的相对位置，导致天线聚焦和指向误差。该项目将开发的实时测量系统将直接测量天线的内部对准，并使LMT的控制系统即使在存在瞬时变形的情况下也能保持高水平的性能。将使用主表面上点之间的16个绝对距离测量来确定14个低空间阶泽尼克多项式的系数，以表征表面变形。另外8个表面和次镜之间的绝对距离测量被用来监视镜面的位置和方向。仿真结果表明，瞬时主镜误差可以减小到约20微米的均方根水平，消除了热变形作为LMT整体面形精度的重要误差源。次镜测量将因未对准而导致的指向误差减少到0.2角秒。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Observations of the Universe at millimeter wavelengths address a broad range of scientific questions. The 50m-diameter Large Millimeter Telescope Alfonso Serrano (LMT) is essential to this work. LMT was built by a partnership between the country of Mexico and the University of Massachusetts Amherst. It is the largest telescope of its type in the world and provides an important research tool for astronomers in the US. Very large antennas like the LMT must be carefully aligned to operate optimally. A major limitation is the result of the internal alignment of the telescope changing as it heats and cools. This project will build a system to measure the shape of the antenna surface and the internal alignment of the mirrors that will allow the LMT to adjust and maintain its alignment. The improvement will be most significant during daylight hours when solar heating of the structure causes the greatest deviations. The project makes extensive use of students and young LMT staff members to train the next generation of scientists and engineers. Research with the LMT connects astronomers in the US and Mexico encouraging scientific collaboration between the two countries.The ultimate performance of a large single dish radio telescope like the LMT is limited by its response to thermal gradients in the antenna structure that lead to deformations of the primary reflector surface, causing a loss of antenna gain. These deformations also change the relative position of the secondary and primary mirrors, leading to antenna focus and pointing errors. The real time metrology system to be developed by this project will directly measure internal alignments in the antenna and allow the LMT’s control systems to maintain a high level of performance even in the presence of transient deformations. Sixteen absolute distance measurements between points on the primary surface will be used to determine the coefficients of 14 low spatial order Zernike polynomials to characterize surface deformations. An additional eight absolute distance measurements between the surface and the secondary mirror are used to monitor the position and orientation of the mirror. Simulations show that transient primary surface mirror errors can be reduced to a level of ~20 microns rms, which removes thermal deformations as an important error source in the LMT’s overall surface accuracy. The secondary mirror measurement reduces pointing errors due to misalignment to the level of 0.2 arcsec rms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.