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Extending the Global Mass Change Data Record: GRACE Follow-On Instrument and Science Data Performance

The 100 years since the publication of Albert Einstein’s theory of general relativity saw significant development of the understanding of the theory, the identification of potential astrophysical sources of sufficiently strong gravitational waves and development of key technologies for gravitational-wave detectors. In 2015, the first gravitational-wave signals were detected by the two US Advanced LIGO instruments. In 2017, Advanced LIGO and the European Advanced Virgo detectors pinpointed a binary neutron star coalescence that was also seen across the electromagnetic spectrum. The field of gravitational-wave astronomy is just starting, and this Roadmap of future developments surveys the potential for growth in bandwidth and sensitivity of future gravitational-wave detectors, and discusses the science results anticipated to come from upcoming instruments.

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Gravitational-wave physics and astronomy in the 2020s and 2030s

The first terrestrial gravitational wave interferometers have dramatically underscored the scientific value of observing the Universe through an entirely different window, and of folding this new channel of information with traditional astronomical data for a multimessenger view. The Laser Interferometer Space Antenna (LISA) will broaden the reach of gravitational wave astronomy by conducting the first survey of the millihertz gravitational wave sky, detecting tens of thousands of individual astrophysical sources ranging from white-dwarf binaries in our own galaxy to mergers of massive black holes at redshifts extending beyond the epoch of reionization. These observations will inform - and transform - our understanding of the end state of stellar evolution, massive black hole birth, and the co-evolution of galaxies and black holes through cosmic time. LISA also has the potential to detect gravitational wave emission from elusive astrophysical sources such as intermediate-mass black holes as well as exotic cosmological sources such as inflationary fields and cosmic string cusps.

The Laser Interferometer Space Antenna: Unveiling the Millihertz Gravitational Wave Sky

The TianQin-1 satellite (TQ-1), which is the first technology demonstration satellite for the TianQin project, was launched on 20 December 2019. The first round of experiment had been carried out from 21 December 2019 until 1 April 2020. The residual acceleration of the satellite is found to be about 1 × 10−10 m/s2/Hz1/2 at 0.1 Hz and about 5 × 10−11 m/s2/Hz1/2 at 0.05 Hz, measured by an inertial sensor with a sensitivity of 5 × 10−12 m/s2/Hz1/2 at 0.1 Hz. The micro-Newton thrusters has demonstrated a thrust resolution of 0.1  μN and a thrust noise of 0.3  μN/Hz1/2 at 0.1 Hz. The residual noise of the satellite with drag-free control is 3 × 10−9 m/s2/Hz1/2 at 0.1 Hz. The noise level of the optical readout system is about 30 pm/Hz1/2 at 0.1 Hz. The temperature stability at temperature monitoring position is controlled to be about ±3 mK per orbit, and the mismatch between the center-of-mass of the satellite and that of the test mass is measured with a precision of better than 0.1 mm.

The first round result from the TianQin-1 satellite

The historic launch of the first several hundred out of 12,000 planned Starlink satellites heralds the arrival of the era of ultra-large satellite constellations If it will bring new opportunities or insurmountable challenges to astronomy will probably depend on whether you are conducting your observations in space or from the surface of the Earth

Hopes and concerns for astronomy of satellite constellations

The Laser Ranging Interferometer (LRI) instrument on the Gravity Recovery and Climate Experiment (GRACE) Follow-On mission has provided the first laser interferometric range measurements between remote spacecraft, separated by approximately 220 km. Autonomous controls that lock the laser frequency to a cavity reference and establish the 5 degrees of freedom two-way laser link between remote spacecraft succeeded on the first attempt. Active beam pointing based on differential wave front sensing compensates spacecraft attitude fluctuations. The LRI has operated continuously without breaks in phase tracking for more than 50 days, and has shown biased range measurements similar to the primary ranging instrument based on microwaves, but with much less noise at a level of 1  nm/sqrt[Hz] at Fourier frequencies above 100 mHz.

In-Orbit Performance of the GRACE Follow-on Laser Ranging Interferometer.

The method involves striking a laser beam (3) on a pyramid (1) that is provided with three side surfaces (6), whose surfaces (7) are designed to be reflective. Each side surface is associated with a light sensor (2), while the laser beam striking on the side surfaces is reflected as the laser beam portions. The laser beam portions are detected by the light sensors and the light intensity of the respective laser beam portions is measured by each light sensor. An incident direction of the laser beam is determined in an evaluation unit (8) by the differences of the measured light intensities. Independent claims are also included for the following: (1) a detector for performing an incident direction determining method; (2) a tracking device for performing an incident direction determining method; (3) a laser communication terminal for a laser communication system on a vehicle, particularly land-, water- or air vehicle; and (4) a method for laser communications with a laser communication system.

Method for determining incident direction of laser beam, involves striking laser beam on pyramid that is provided with three side surfaces, whose surfaces are designed as reflective, where each side surface is associated with light sensor

Martin Hinz

Papers

In-Orbit Performance of the GRACE Follow-on Laser Ranging Interferometer.

Method for determining incident direction of laser beam, involves striking laser beam on pyramid that is provided with three side surfaces, whose surfaces are designed as reflective, where each side surface is associated with light sensor