sfsim is a realistic 3D space flight simulator under development. You can already download the sfsim playtest build on Steam and try it out. sfsim uses true celestial positions of Earth and Sun from NASA. Use an advanced single-stage-to-orbit space craft to take off, orbit the planet, perform reentry, and land back on Earth. sfsim features a true to scale Earth planet using NOAA elevation data and procedurally generated volumetric clouds.