Reconstructing the cruise-phase trajectory of deep-space probes in a general relativistic framework:An application to the Cassini gravitational wave experiment

Einstein’s theory of general relativity is playing an increasingly important role in fields such as interplanetary navigation,astrometry,and metrology.Modern spacecraft and interplanetary probe prediction and estimation platforms employ a perturbed Newtonian framework,supplemented with the Einstein-Infeld-Hoffmann n-body equations of motion.While time in Newtonian mechanics is formally universal,the accuracy of modern radiometric tracking systems necessitate linear corrections via increasingly complex and error-prone post-Newtonian techniques—to account for light deflection due to the solar system bodies.With flagship projects such as the ESA/JAXA BepiColombo mission now operating at unprecedented levels of accuracy,we believe the standard corrected Newtonian paradigm is approaching its limits in terms of complexity.In this paper,we employ a novel prototype software,General Relativistic Accelerometer-based Propagation Environment,to reconstruct the Cassini cruise-phase trajectory during its first gravitational wave experiment in a fully relativistic framework.The results presented herein agree with post-processed trajectory information obtained from NASA’s SPICE kernels at the order of centimetres.

Optical observations of LIGO source GW 170817 by the Antarctic Survey Telescopes at Dome A,Antarctica

The LIGO detection of gravitational waves(GW) from merging black holes in 2015 marked the beginning of a new era in observational astronomy. The detection of an electromagnetic signal from a GW source is the critical next step to explore in detail the physics involved. The Antarctic Survey Telescopes(AST3),located at Dome A, Antarctica, is uniquely situated for rapid response time-domain astronomy with its continuous night-time coverage during the austral winter. We report optical observations of the GW source(GW 170817) in the nearby galaxy NGC 4993 using AST3. The data show a rapidly fading transient at around 1 day after the GW trigger, with the i-band magnitude declining from 17:23 ± 0:13 magnitude to 17:72 ± 0:09 magnitude in ~1:8 h. The brightness and time evolution of the optical transient associated with GW 170817 are broadly consistent with the predictions of models involving merging binary neutron stars. We infer from our data that the merging process ejected about ~10^(-2) solar mass of radioactive material at a speed of up to 30% the speed of light.

Harnessing the power of complex light propagation in multimode fibers for spatially resolved sensing

The propagation of coherent light in multimode optical fibers results in a speckled output that is both complex and sensitive to environmental effects.These properties can be a powerful tool for sensing,as small perturbations lead to significant changes in the output of the fiber.However,the mechanism to encode spatially resolved sensing information into the speckle pattern and the ability to extract this information are thus far unclear.In this paper,we demonstrate that spatially dependent mode coupling is crucial to achieving spatially resolved measurements.We leverage machine learning to quantitatively extract the spatially resolved sensing information from three fiber types with dramatically different characteristics and demonstrate that the fiber with the highest degree of spatially dependent mode coupling provides the greatest accuracy.