Stephen Merkowitz: NASA currently offers a network of space geodetic ground stations that do Very Long Baseline Interferometry (VLBI), satellite laser ranging (SLR), and [global navigation satellite system] GNSS or GPS tracking. The new space geodesy project will develop and implement the next-generation systems. The current systems are 20-30 years old. One of the primary drivers for upgrading the system is sea-level measurement, where you would like to be able to make those measurements at the millimeter level and have them be stable over the years, so you can do repeated measurements.
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