It seems that SDG-5 was last heard from about two hours after launch. We are very much in need of any telemetry that might have been copied during the flight - if you jotted anything down, or even if you simply heard the balloon and remember what time it was, please drop us a line!
Initial suspicions are that the new end fittings failed upon pressurization. The SDG-5 design differed from early balloons in the series by using a non-metallic end fitting - a failure of this component would immediately down the balloon.
So if it's down, where is it? Most likely somewhere in south-western Ontario, Canada. Any amateurs in the area might want to tune up their radios and have a listen on 28.636 - you might just help recover our missing flight!