Links for 2019-04-12

  • _First M87 Event Horizon Telescope Results. III. Data Processing and Calibration_

    ‘We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3 mm radio wavelength observations of the supermassive black hole candidate at the center of the radio galaxy M87 and the quasar 3C 279, taken during the 2017 April 5–11 observing campaign. These global very long baseline interferometric observations include for the first time the highly sensitive Atacama Large Millimeter/submillimeter Array (ALMA); reaching an angular resolution of 25 ?as, with characteristic sensitivity limits of ?1 mJy on baselines to ALMA and ?10 mJy on other baselines. The observations present challenges for existing data processing tools, arising from the rapid atmospheric phase fluctuations, wide recording bandwidth, and highly heterogeneous array. In response, we developed three independent pipelines for phase calibration and fringe detection, each tailored to the specific needs of the EHT. The final data products include calibrated total intensity amplitude and phase information. They are validated through a series of quality assurance tests that show consistency across pipelines and set limits on baseline systematic errors of 2% in amplitude and 1° in phase. The M87 data reveal the presence of two nulls in correlated flux density at ?3.4 and ?8.3 G? and temporal evolution in closure quantities, indicating intrinsic variability of compact structure on a timescale of days, or several light-crossing times for a few billion solar-mass black hole. These measurements provide the first opportunity to image horizon-scale structure in M87.’

    (tags: papers data big-data telescopes eht black-holes astronomy)

  • Autonomous Precision Landing of Space Rockets – Lars Blackmore

    from ‘Frontiers of Engineering: Reports on Leading-Edge Engineering’ from the 2016 Symposium, published by the National Academies Press, regarding the algorithms used by SpaceX for their autonomous landings:

    The computation must be done autonomously, in a fraction of a second. Failure to find a feasible solution in time will crash the spacecraft into the ground. Failure to find the optimal solution may use up the available propellant, with the same result. Finally, a hardware failure may require replanning the trajectory multiple times. Page 39 Suggested Citation:”Autonomous Precision Landing of Space Rockets – Lars Blackmore.” National Academy of Engineering. 2017. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2016 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/23659. × Save Cancel A general solution to such problems has existed in one dimension since the 1960s (Meditch 1964), but not in three dimensions. Over the past decade, research has shown how to use modern mathematical optimization techniques to solve this problem for a Mars landing, with guarantees that the best solution can be found in time (Açikme?e and Ploen 2007; Blackmore et al. 2010). Because Earth’s atmosphere is 100 times as dense as that of Mars, aerodynamic forces become the primary concern rather than a disturbance so small that it can be neglected in the trajectory planning phase. As a result, Earth landing is a very different problem, but SpaceX and Blue Origin have shown that this too can be solved. SpaceX uses CVXGEN (Mattingley and Boyd 2012) to generate customized flight code, which enables very high-speed onboard convex optimization.

    (tags: spacex blue-origin convex-optimization space landing autonomous-vehicles flight algorithms)

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