text: The value of this constant became important with the beginning of spaceflight in the 1950s, and great effort was expended to determine it as accurately as possible during the 1960s. Sagitov (1969) cites a range of values reported from 1960s high-precision measurements, with a relative uncertainty of the order of 10−6.
  During the 1970s to 1980s, the increasing number of artificial satellites in Earth orbit further facilitated high-precision measurements,
  and the relative uncertainty was decreased by another three orders of magnitude, to about  (1 in 500 million) as of 1992.
  Measurement involves observations of the distances from the satellite to Earth stations at different times, which can be obtained to high accuracy using radar or laser ranging.
  Heliocentric gravitational constant
  G, the gravitational parameter for the Sun as the central body,
  is called the heliocentric gravitational constant or geopotential of the Sun and equals
  The relative uncertainty in G, cited at below 10−10 as of 2015, is smaller than the uncertainty in G
  because G is derived from the ranging of interplanetary probes, and the absolute error of the distance measures to them is about the same as the earth satellite ranging measures, while the absolute distances involved are much bigger.