27 years ago today, the space shuttle Challenger exploded 73 seconds into flight, killing all seven aboard.

While the accident was caused by a faulty o-ring in the shuttle's right solid rocket booster, a much bigger problem at NASA was found by the investigators: NASA had become complacent after decades of routine flights.

Discovery's When We Left Earth chronicles manned space flight, and helps explain how NASA got into the mess it found itself with Challenger. The films have tons of original NASA footage, interviews and more. It's a real treat to watch.

You're probably better off getting the Blu-Ray edition, but its backordered. Thankfully, the DVD version is just $14 for Amazon Prime Members