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Nowadays, the TRF is realized by station coordinates and velocities for a globally distributed set of ground stations using a combination of the four major space geodetic techniques: GNSS-based determinations of the geocenter motion suffer from orbit modeling deficiencies due to an inherent coupling of the GNSS orbit dynamic parameters: the GNSS geocenter Z-component is strongly correlated with the parameterization of the Solar Radiation Pressure (SRP) (Meindl et al. 2013). With only limited a priori knowledge about the non-conservative forces acting on GNSS satellites, we must incorporate additional empirical orbit parameters into the solution, i.e., Empirical CODE Orbit Model or Jet Propulsion Laboratory GSPM. The errors in the orbit model, as well as the correlations between the estimated parameters (Rebischung et al. 2014), introduce spurious orbit-related signals in the GNSS-based geocenter motion estimates (Meindl et al. 2013; Rodriguez-Solano et al. 2014). The consistency between GNSS-based and SLR-based geocenter motion estimates can be improved by using satellite macromodels (Zajdel et al. 2021). Another way to improve the GNSS-based geocenter motion is the combined multi-GNSS processing (Scaramuzza et al. 2018) or the inclusion of Galileo satellites on an eccentric plane (Zajdel et al. 2021). DORIS as the third satellite technique is in principle also sensitive to the CM of the Earth. DORIS benefits from the well-distributed network of stations, but trails other geodetic techniques in terms of the quality of station coordinates because of the limitation of non-gravitation perturbing forces modeling and precise orbit determination of active satellites equipped with DORIS receivers. Moreover, the problems mentioned for GNSS also apply to the DORIS system. Yet, SRP modeling error on the Jason-type satellites can be identified and mitigated without compromising the Z geocenter estimate (Couhert et al. 2018).

The OHU can be estimated with an accuracy of a few tenths of W m \( Sweetening the deal even further are a quartet of minifigures; Vice Admiral Sloane, a pilot for the TIE Bomber, a Gonk Droid, and the iconic Darth Vader complete with lightsaber.

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For example, the definition of "space" is the absence of anything, ie, nothing. Since space is nothing at all, then space cannot be bent, since one cannot bend nothing. There is nothing to bend. Of course, there is another way of looking at it: in the time it has taken you to read this article, you've already travelled seven minutes or so into the future. You're welcome. On shorter timescales, GNSS stations also record Earth’s elastic response to surface mass redistribution within the climatic system (mainly continental water storage, atmosphere and ocean). Dense networks of permanent GNSS stations can now be used to derive soil and snow water content at seasonal timescales, but has also provided evidence for extreme droughts, especially in California (see, e.g., Argus et al. 2014; Fu et al. 2015; Jiang et al. 2022). GNSS time series from dense networks can be used to refine the information provided by space gravimetry missions (GRACE and GRACE-FO) at longer spatial wavelengths (see section Long-wavelength gravity field). Amplitude and spatial extent of surface water mass variations can be inferred from both vertical and horizontal deformation measurements. In particular, horizontal displacements help to refine the determination of the location and the spatial extent of the load. This elastic Earth’s response to surface loads has to be separated from a longer-term deformation, which can only be obtained with a more accurate and stable reference frame as proposed by the GENESIS project.

So much for time travel based on relativity. What about the other great theory of the Universe: quantum mechanics? The ITRF long-term origin is defined by SLR, the most accurate satellite technique in sensing the Earth’s CM. The ITRF long-term scale, however, is defined by an average of the SLR and VLBI intrinsic scales. The consistency of these scales still needs to be improved, since both techniques are subject to systematic errors and other technical limitations, such as time and range biases for SLR, antenna deformation for VLBI, etc. The GENESIS mission will help to solve these inconsistencies. The ITRF orientation and its time evolution are defined to be the same for the successive ITRF realizations. Up to now the geocenter motion is traditionally measured by SLR using the observations to geodetic satellites (see Fig. 3). The geodetic satellites such as LAGEOS or LARES are considered to be well suited for determining the geocenter motion owing to their mission characteristics, such as orbit altitude, low area-to-mass ratio, and thus minimized non-gravitational orbit perturbing forces. Until now, determination of geocenter coordinates based on the SLR observations to active Low-Earth Orbit (LEO) satellites was limited because of issues in non-gravitational force modeling acting on LEO satellites. In principle, the geocenter coordinates should be well determined from any satellite mission that is continuously observed and has processed orbits of superior quality. Therefore, GENESIS can introduce an alternative for the geocenter recovery w.r.t. passive geodetic satellites.This is where time travel can come in and it is scientifically accurate and there are real-world repercussions from that," says Emma Osborne, an astrophysicist at the University of York, in the UK. Given that GENESIS will provide a direct link between the kinematic (VLBI, quasar-based) and dynamic (satellite-based) reference frames and is expected, thus, to improve the consistency of the TRF, CRF, and EOP realizations, all the above scientific domains will be positively impacted, extending thus the challenges of GENESIS well beyond its first scope. The TRF is the realization of the TRS and is currently provided by precisely determined coordinates and velocities of physical points on the Earth’s surface. The main physical and mathematical properties of a TRS (at the definition and conventions level) or of the TRF (at the realization level) include each its origin, scale, orientation, and their time evolution. The center of mass (CM) of the Earth System, or geocenter, as the realized origin of the TRF on long-term scales, needs to be accurately determined including its temporal motion (e.g., Petit and Luzum 2010). The temporal variations of the geocenter represent a component of mass change (at spherical harmonic degree one) that is not directly observable from a mass-change mission such as GRACE-FO (Wu et al. 2012). While the degree one component of mass change can be derived from a combination of GRACE data with ocean model output (e.g., Swenson et al. 2008; Sun et al. 2016, 2017) or space geodetic techniques such as GNSS, SLR (e.g., Fritsche et al. 2009; Glaser et al. 2015), a high-quality TRF solution furnished by space geodesy that allows a matching with the temporal resolution of the GRACE-FO data would be highly desired (see section Long-wavelength gravity field for more details). While time travel is fundamental to Doctor Who, the show never tries to ground the Tardis' abilities in anything resembling real-world physics. It would be odd to complain about this: Doctor Who has a fairy-tale quality and doesn't aspire to be realistic science fiction.