Space-time reference with an optical link

Abstract

We describe a method for realizing a high performance Space--Time Reference (STR) using a stable atomic clock in a precisely defined orbit and synchronizing the orbiting clock to high--accuracy atomic clocks on the ground. The synchronization would be accomplished using a two--way lasercom link between ground and space. The basic concept is to take advantage of the highest--performance cold--atom atomic clocks at national standards laboratories on the ground and to transfer that performance to an orbiting clock that has good stability and that serves as a "frequency--flywheel" over time--scales of a few hours. The two--way lasercom link would also provide precise range information and thus precise orbit determination (POD). With a well-defined orbit and a synchronized clock, the satellite could serve as a high--accuracy Space--Time Reference, providing precise time worldwide, a valuable reference frame for geodesy, and independent high--accuracy measurements of GNSS clocks. With reasonable assumptions, a practical system would be able to deliver picosecond timing worldwide and millimeter orbit determination.

Effect of atmospheric anisoplanatism on earth-to-satellite time transfer over laser communication links

“…Our analytic model shows that a direct-detection two-way laser communication link can provide sub-picosecond timing between ground and space. This approach could support the next generation of atomic clocks, geodetic references, and global navigation satellite systems [8].…”

“…Exploiting free-space laser communication links between Earth and space for time transfer is particularly attractive [8]. These links already provide pointing and tracking means, and already require accurate timing for efficient signal decoding.…”

“…also shows the total time transfer standard deviation is computed using SNR per unit time 0 γ given by Eq (8)…”

Using quantum optical sensors for determining the Earth’s gravity field from space

“…This makes optical clocks applicable for the unification of local height systems (Wu et al 2018) or realizing a consistent global height reference system (Mehlstäubler et al 2018). They are also highly relevant for various geodetic and geophysical applications, such as the realization of a space-time reference system (Berceau et al 2016), monitoring vertical surface motions (Bondarescu et al 2015) and the determination of the Earth's gravity field (Müller et al 2018). Using clocks for determining a local geopotential model with a high spatial resolution was quantitatively investigated by Lion et al (2017).…”

Systematic evaluation of a 171Yb optical clock by synchronous comparison between two lattice systems

“…The increasingly high measurement precision has led to new tests of fundamental physics, such as the gravitational redshift, and the constancy of fundamental constants 11 – 14 . Along with the verification of physical theories, dedicated optical networks for linking distant optical clocks are being established 15 , thereby enabling applications in fields including time and frequency dissemination, geodesy, and satellite-based navigation 16 – 19 . Further, these achievements will open up the possibility of a redefinition of the SI second in the future 20 , 21 .…”