Gravitational Physics via Lunar Laser Ranging: Optimizing Data Quality

引力是自然界最明显的力，但实际上是基本力中最弱的，因此也是最缺乏检验的。爱因斯坦的广义相对论是目前我们对引力的最好描述，它与量子力学根本不相容，很可能在未来被更完整的理论所取代。一个修正的理论将预测太阳系中的小偏差，这可能对我们理解整个宇宙产生深远的影响。月球激光测距（LLR），其中从望远镜发射的短激光脉冲被美国宇航员和苏联着陆器放置在月球上的反射器反射，几十年来通过绘制月球轨道的形状来产生各种领先的重力测试。该小组建议继续与阿帕奇点天文台月球激光测距行动（APOLLO）进行前沿观测，以努力使重力受到迄今为止最严格的测试。阿波罗位于新墨西哥州南部一个9,200英尺高的山顶上，在测量月球轨道时引入了一种新的毫米精度。然而，不完整的模型迄今无法确认准确性。因此，该小组将寻求建立一个校准系统，以确保APOLLO满足其毫米测量目标，除了继续观测活动。拟议的工作将以多种方式使更广泛的社区受益。在智力方面，提高我们对引力的认识，为各种各样的宇宙学家、天体物理学家、粒子物理学家和弦理论家提供了信息。这项工作也将有助于地球和行星科学，特别是通过超导重力仪产生的测量。APOLLO团队将继续参与教育和推广活动的记录，毫无疑问，将继续通过印刷品，网络，广播和电视媒体吸引公众的兴趣。在APOLLO的上级观测的其他属性中，在分钟的时间尺度上对所有五个月球反射器进行常规测距大大提高了我们测量月球方向和身体变形的能力。这些信息可以更精确地确定月球质心的路径，从而促进基本引力的测试。与此同时，更高精度的距离测量，加上来自阿帕奇角天文台超导重力仪和2.5公里外高质量全球定位系统站的数据，将大大提高我们对天文台相对于地球质心的瞬时位置的理解（重力测试所需的）通过暴露微妙的地球动力学，必须纳入模型。LLR测量提供了强等效原理、牛顿引力常数的时间变化率、重力磁性、平方反比定律和优先框架效应的最佳可用测试。除了这些经典的引力测试之外，阿波罗还将允许测试物理学中与暗能量、额外维度和违反洛伦兹不变性有关的新想法。这里提出的努力的很大一部分是绝对校准系统的基础上的铯时钟标准，低抖动短脉冲激光器，和精密间隔计数器的建设。该系统将对APOLLO的基本测量进行独立检查，可能识别故障并确认其后续补救措施。

Gravity, the most evident force of nature, is in fact the weakest of the fundamental forces, and consequently the most poorly tested. Einstein's general relativity, which is currently our best description of gravity, is fundamentally incompatible with quantum mechanics and is likely to be replaced by a more complete theory in the future. A modified theory would predict small deviations in the solar system that could have profound consequences for our understanding of the Universe as a whole. Lunar laser ranging (LLR), in which short laser pulses launched from a telescope are bounced off of reflectors placed on the moon by U.S. astronauts and Soviet landers, has for decades produced various leading tests of gravity by mapping the shape of the lunar orbit to high precision. The group proposes to continue conducting leading-edge observations with the Apache Point Observatory Lunar Laser-ranging Operation (APOLLO), in an effort to subject gravity to the most stringent tests yet. APOLLO, situated atop a 9,200 ft summit in Southern New Mexico, introduces a new regime of millimeter-precision in measuring the lunar orbit. However, incomplete models are thus far unable to confirm the accuracy. The group will therefore seek to build a calibration system to ensure that APOLLO meets its millimeter measurement goal, in addition to continuing the observation campaign. The proposed work will benefit the broader community in a number of ways. On the intellectual front, improving our knowledge of gravity informs a diverse range of cosmologists, astrophysicists, particle physicists, and string theorists. The effort would also contribute to Earth and planetary science, especially via measurements produced by the superconducting gravimeter. The APOLLO team will continue a track record of engagement in education and outreach activities, and will no doubt continue to attract public interest through print, web, radio, and television media.Among other attributes that contribute to APOLLO's superior observations, routine ranging to all five lunar reflectors on timescales of minutes dramatically improves our ability to gauge lunar orientation and body distortion. This information allows a more precise determination of the path for the Moon's center of mass, thereby facilitating tests of fundamental gravity. Simultaneously, higher precision range measurements, together with data from a superconducting gravimeter at the Apache Point Observatory and from a high-quality Global Positioning System (GPS) station 2.5 km away, will greatly improve our understanding of the instantaneous location of the Observatory with respect to the Earth's center of mass (needed for the gravitational tests) by exposing subtle Earth dynamics that must be incorporated into the model. LLR measurements provide the best available tests of the strong equivalence principle, the time-rate-of-change of Newton's gravitational constant, gravitomagnetism, the inverse-square law, and preferred frame effects. In addition to these classical gravitational tests, APOLLO will permit testing of new ideas in physics relating to dark energy, extra dimensions, and violations of Lorentz Invariance. A large part of the effort proposed here is the construction of an absolute calibration system based on a cesium clock standard, a low-jitter short-pulse laser, and a precision interval counter. This system will provide an independent check of APOLLO's fundamental measurement, potentially identifying faults and confirming their pursuant remediation.