I'm really too busy to blog this week, but I wanted to briefly note today's 50th anniversary of the launch of Explorer 1 on January 31, 1958. Developed by JPL, Explorer 1 was the United States' first successful satellite. Astroprof has a good post on Explorer 1.
The picture shows an add-on version of Explorer 1 simulated in Orbiter (you can see the first stage falling away in the smoke following stage separation). This add-on is by Jim Williams and it features a launch autopilot and some sounds, including the original launch countdown. Another Explorer 1 add-on was released yesterday but I don't know too much about that version.