Space geodetics is modern technology that uses satellites and radio telescopes to routinely measure the dimensions of the Earth and plate motions of the continents to sub-centimetre accuracy. During the early 1990s, when enough ground stations were established to form a global network,
the global excess in radius was found to be 18 mm/year – i.e. the measurements showed that the Earth was expanding by 18 mm/year.
This value was considered to be “extremely high” when compared to expected deglaciation rates during melting of the polar ice-caps, estimated at less than 10 mm/year. The researchers in fact "expected that most … stations will have up-down motions of only a few mm/yr" and went on to recommend the vertical motion be "restricted to zero, because this is closer to the true situation than an average motion of 18 mm/yr". This recommendation is now reflected in current mathematical solutions to the global radius, where global solutions are effectively constrained to zero.
These recommendations are justified from a constant Earth radius Plate Tectonic perspective. The 18 mm/year excess was considered to be an error in atmospheric correction, so was simply zeroed out. What must be appreciated is that without an acknowledgment of a potential increase in Earth radius NASA had no option but to correct this value to zero, and hence adopt a static Earth radius premise. From an Expansion Tectonic Earth perspective, however, the 18 mm/year excess equates with a present day value of 22 mm/year increase in Earth radius, determined independently from measurements of areas of sea floor spreading.
Expansion Tectonics Page 2 - James Maxlow
