NASA
National Aeronautics and Space Administration

ESA
European Space Agency

JAXA
Japan Aerospace Exploration Agency

ISS
International Space Station

HST
Hubble Space Telescope

LEO
Low Earth Orbit

MEO
Medium Earth Orbit

GEO
Geostationary Orbit

LUNAR
Lunar (often used in the context of lunar missions)

RCS
Reaction Control System

PDR
Preliminary Design Review

CDR
Critical Design Review

SRM
Solid Rocket Motor

TLE
Two-Line Element (for tracking satellites)

ASTRO
Astronaut (commonly used in mission contexts)