Implications on the Design of Next Generation Gravity Missions (NGGMs) from Gravitational Reference Sensor Tests on the ESA-NASA Pathfinder Mission for the LISA Gravitational Wave Mission

The main objective of the recently launched GRACE Follow-On Mission (GFO) is to continue the roughly monthly determinations of variations in the global gravity field that were started by the GRACE mission (2002 - 2017). However, with much improved accuracy for measuring changes in the separation of the 2 satellites by laser ranging interferometry (LRI) having been demonstrated on GFO, major reductions in the relative acceleration noise level in possible designs for NGGMs appear to be worth considering. Such reductions would be of particular value in regions where local models of the geopotential time variations are being developed. And the necessary high accuracy for isolating reference test masses from both internal and external disturbances has been demonstrated on the LISA Pathfinder mission. For the limited objective of determining variations in the geopotential along the mean orbit, it appears that strongly reducing the relative acceleration noise by drag-free operation of the satellites or a high degree of AC drag-compensation would deserve a high priority in the design. We have investigated the accuracy achievable at GFO altitude with what we call Along Track Analysis in a limited study where only acceleration noise and the distance measurement noise are considered.