IAU: Minor Planet Center - http://www.cfa.harvard.edu/iau/mpc.html
The official body that deals with astrometric observations, and orbits of minor planets, asteroids, and comets. |
National Space Science Data Center - http://nssdc.gsfc.nasa.gov/
Provides access to a wide variety of astrophysics, space physics, solar physics, lunar, and planetary data from NASA space flight missions, in addition to selected other data, models, and software. |
PDS - Planetary Data System - http://pds.jpl.nasa.gov/
Solar system exploration science data archive, maintained at JPL. |