I've only just seen the video, but it looks like today's Antares launch had an engine failure a few seconds after liftoff, fell back on the pad, and exploded. Pending more data, it looks like the big questions going forward will be the NK-33/AJ-26 engines, and pad damage.
Video at http://www.clickorlando.com/news/nasa-rocket-explodes-shortly-after-launch/29392528
Several seconds after liftoff, the exhaust plume seems to double in width/brightness for a good part of a second, flickers, then there's an explosion around the aft end of the rocket, no further engine plume, and the vehicle falls back onto the pad area with about the results you'd expect. (Nobody hurt, according to initial reports.)
Massively sparse data for now, of course, but it looks like the initial failure may, repeat may, have been a massive fuel leak - a split nozzle? - with that engine exploding part of a second later, presumably taking out the second engine in the process.
Henry V
