Not sure if even Rutan is doing exhaustive testing.

Test firing an engine is not exhaustive testing.

Test firing an engine with the flight propulsion system is not exhaustive testing.

Doing all that PLUS putting a complete vehicle in an environmental chamber to test the effects of heat, cold, and vacuum only begins to count as exhaustive testing.

I'm not sure what you are talking about. Who cares if he doesn't test his plane in a vacuum, heat, cold chamber? He's FLYING it, which is a hell of a lot more than the other X Prize contestants are doing right now. Why would he waste money on simulations when he can make adjustments to the design with real world data?

Waiting till you're flying to discover the effects of vacuum or cold on an airframe is how people get killed.

Scaled Composites had a lot of experience with high altitude aircraft, before SS1 was even flown. Like any test program, the flights involved gradual increases in the operational envelope. Are there risk involved? Sure, but that's why they call these guys test pilots and these planes experimental.

I'd still say his craft is a lot safer than any of the other contest entries, for the simple reason that it has been tested up to supersonic speeds with no major issues.

Now it's entirely possible, given Rutan's secrecy and budget., that the SpaceShipOne airframe has been tested in a vacuum chamber.

Possible, but doubtful (there's not many of them, and they're already backscheduled for research purposes), and somewhat unnecessary: the pressure difference between sea level and deep space isn't really as much as most people think, and the effects of exoatmospheric flights on airframes and pressurized compartments are very well-known. If Rutan has included the appropriate failsafes (and the failsafes for the failsafes), vacuum testing would be completely unnecessary.

Besides, as Bullspace said, Scaled Composites has done some very-high-altitude work, including Voyager. He knows how to build to accomodate for a pressure differential.

Ah canadian arrow is buidling on V2s. They were flight tested to ~100 km two thousand times and to ~150km about 60 times. As long as they don't change the structure or shape to much then all that data is theirs.

Yes, it's a proven design, but I'd suspect German manufacturing in WWII was more high quality than Canadian manufacturing today.

The X-15 designers would regard that attitude as simplistic and naive. The X-15 underwent heat and vacuum chamber testing, yet still on SEPARATE occasions while doing over Mach 4 had accidental deployments of the nose gear and a main gear.

Rutan's testing approach strikes me as balanced between aggressive and cautious. I expect that SpaceShipOne would likely survive if launched tomorrow with a full burn time. But what's the point when you can take a few extra months and make it very very likely to be successful. On the other hand he is being aggressive -- otherwise he would still be in the planning stage. Don't forget that SpaceShipOne has had some problems, but the incremental testing process has allowed them to be found and fixed.