I've resuffled Space Science News and broken it into three pieces:
Space Science News: The emphasis is mainly on near earth technology and space exploration
astronaut, cassini, deep space network, earth observation, galaxy evolution explorer, geosynchronous orbit, hubble, huygens, iss, lunar exploration, mars exploration, mars global surveyor, nasa, satellite, soyuz, space probe, space shuttle, space tourism, spirit rover, spitzer
Solar System News: Science and Astronomy solely focussed on the solar system
asteroids, solar system, venus, comets, solar storms, earth, ,jupiter, sunspots, magnetic storms, mars, mercury, titan, meteorites, near earth objects, neptune, planets, pluto, saturn, solar flares, uranus
Astronomy News: Theoretical and Cosmological type stuff
astrobiology, astrophysics, big bang, binary stars, black holes, chandra, cosmology, dark matter, galaxies, gamma ray bursts, nebulae, nova, observatory, pulsars, quasars, radio astronomy, seti, star clusters, stars, supervova.
The system isn't perfect but its a good chance to see how it scales - the question is - how many keyword cluster units do you need to completely cover a field like astronomy?