Apollo Lunar Surface Journal – A NASA collection of all sort of Apollo stuff
Atomic Rockets – A great collection of information about spaceflight, including all the gritty details like the Oberth Effect
Hop’s Blog – Special Articles addressing specific issues about how to get from one planet to another
How Many People Are in Space Right Now – Self-Explanatory – possibly the most elegant site on the internet
Interplanetary Hohmann Transfer Guide – voneiden’s step-by-step guide on how to get from one planet to another in Kerbal Space Program on the KSP forum.
Jeff Russell’s Starship Dimensions – Exactly what it says – a visual scaled comparison of starships from the length and breadth of science fiction. For Internet Explorer users, it is also interactive, allowing you to click and drag the images for direct comparisons. By using pages with different scales, this site includes everything from an Imperial Probe Droid to Rama, from Serenity to the Vorlon Planet Killer.
Kerbal Space Program – Where you can get Kerbal Space Program
Kerbal SpacePort – Where you can get mods for KSP.
NASA TV Schedule – When you can watch all the fun stuff NASA does.
Solar System Live – Check out the position of the planets in a heliocentric model (as opposed to Earth-centric or where they are in the sky) at any given time
Jeff Russell’s Starship Dimensions – Exactly what it says – a visual scaled comparison of starships from the length and breadth of science fiction. For Internet Explorer users, it is also interactive, allowing you to click and drag the images for direct comparisons. By using pages with different scales, this site includes everything from an Imperial Probe Droid to Rama, from Serenity to the Vorlon Planet Killer.