| M | Messier | - | Atmospheric Research Center |
| MACHO | MAssive Compact Halo Object | - | Atmospheric Research Center |
| MACRO | Monopoles | - | Atmospheric Research Center |
| MACS | Modular Attitude Control System | - | Atmospheric Research Center |
| MARS | Series Of Soviet Mars Spacecraft | - | Atmospheric Research Center |
| MAS | Millimeter-wave Atmospheric Sounder | - | Atmospheric Research Center |
| MB | Manned Base | - | Atmospheric Research Center |
| MBB | Messerschmitt-Belkow-Blohm | - | Atmospheric Research Center |
| MCC | Mission Control Center | - | Atmospheric Research Center |
| MCCC | Maragone Convection On Closed Containers | - | Atmospheric Research Center |
| MDSSC | McDonnell Douglas Space Systems Corp | - | Atmospheric Research Center |
| MECO | Main Engine CutOff | - | Atmospheric Research Center |
| MET | Mission Elapsed Time | - | Atmospheric Research Center |
| MEV | Mars Excursion Vehicle | - | Atmospheric Research Center |
| MFPE | Misson From Planet Earth | - | Atmospheric Research Center |
| MFV | Main Fuel Valve | - | Atmospheric Research Center |
| MIMR | Multifrequency Imaging Microwave Radiometer | - | Atmospheric Research Center |
| MISR | Multiangle Imaging Spectro-Radiometer | - | Atmospheric Research Center |
| MITI | Ministry Of International Trade And Industry | - | Atmospheric Research Center |
| MJD | Modified Julian Date | - | Atmospheric Research Center |
| ML | Mobile Launcher | - | Atmospheric Research Center |
| MLI | Multi-Layer Insulation | - | Atmospheric Research Center |
| MLP | Mobile Launch Platform | - | Atmospheric Research Center |
| MLS | Microwave Limb Sounder | - | Atmospheric Research Center |
| MMCC | Mission Management And Control Centre | - | Atmospheric Research Center |
| MMH | MonoMethyl Hydrazine | - | Atmospheric Research Center |
| MMPO | Mission Management And Planning Office | - | Atmospheric Research Center |
| MMS | Multi-mission Modular Spacecraft | - | Atmospheric Research Center |
| MMT | Multiple Mirror Telescope | - | Atmospheric Research Center |
| MMU | Manned Maneuvering Unit | - | Atmospheric Research Center |
| MNRAS | Monthly Notices Of The Royal Astronomical Society | - | Atmospheric Research Center |
| MOC | Mars Observer Camera | - | Atmospheric Research Center |
| MODE | Middeck Zero-Gravity Dynamics Experiment | - | Atmospheric Research Center |
| MODIS | Moderate Resolution Imaging Spectrometer | - | Atmospheric Research Center |
| MODIS-N | MODIS-Nadir | - | Atmospheric Research Center |
| MODIS-T | MODIS-Tilt | - | Atmospheric Research Center |
| MOL | Manned Orbiting Laboratory | - | Atmospheric Research Center |
| MOLA | Mars Observer Laser Altimeter | - | Atmospheric Research Center |
| MOMS | Modular Optoelectronic Multispectral/Stereo Scanner | - | Atmospheric Research Center |
| MOMV | Manned Orbital Maneuvering Vehicle | - | Atmospheric Research Center |
| MOPITT | Measurements Of Pollution In The Troposphere | - | Atmospheric Research Center |
| MOTV | Manned Orbital Transfer Vehicle | - | Atmospheric Research Center |
| MPC | Minor Planets Circular | - | Atmospheric Research Center |
| MPEC | Multi-Purpose Experiment Canister | - | Atmospheric Research Center |
| MPESS | Multiple Purpose Experiment Support Structure | - | Atmospheric Research Center |
| MRIR | Medium Resolution Infrared Radiometer | - | Atmospheric Research Center |
| MRO | Memory Read-Out | - | Atmospheric Research Center |
| MRSR | Mars Rover And Sample Return | - | Atmospheric Research Center |
| MRSRM | Mars Rover And Sample Return Mission | - | Atmospheric Research Center |
| MS | Main Sequence | - | Atmospheric Research Center |
| MSFC | Marshall Space Flight Center | - | Atmospheric Research Center |
| MSOCC | Multisatellite Operations Control Center | - | Atmospheric Research Center |
| MSS | Multispectral Scanner | - | Atmospheric Research Center |
| MSU | Microwave Sounding Unit | - | Atmospheric Research Center |
| MTC | Man Tended Capability | - | Atmospheric Research Center |
| MTFF | Columbus Man-Tended Free-Flyer | - | Atmospheric Research Center |
| MTPE | Mission To Planet Earth | - | Atmospheric Research Center |
| MVI | Microgravity Vestibular Investigation | - | Atmospheric Research Center |
