MWR	Microwave ranging
GRACE	Gravity recovery and climate experiment
EGF	Earth’s gravity field
DEM	Digital elevation models
SFF	Spacecraft formation flying
LEO	Low Earth orbit
HEO	Highly elliptical orbit
DOWR	Dual one-way ranging
HIL	Hardware in loop
6-DOF	Six degrees of freedom
CAN	Controller Area Network
GNC	Guidance, navigation, and control
ISL	Inter-satellite-link
NASA	National Aeronautics and Space Administration
ESA	European Space Agency
EGFD	Earth’s gravity field detection
TT&C	Telemetry, track, and command
LOS	Line of sight
USO	Ultra-stable oscillator
KBR	K-band ranging
IF	Intermediate frequency
OBDH	On-board data handling
RF	Radio frequency
POD	Precise orbit determination
LO	Local oscillator
NCO	Numerically controlled oscillator
SAR	Synthetic aperture radar
In-SAR	Interferometric synthetic-aperture radar
GA	Gravitational accelerations
NGA	Non-gravitational accelerations
RMS	Root mean square