7/27/2007 12:42:17 P.M. Pacific Daylight Time

Kent,

I have a friend who, although he doesn't work for Scaled Composites, is
close to those who do, including Burt Rutan. He is still receiving only
sketchy reports but he has put together what he thinks happened.

First, SOME OF THE CONCLUSIONS HERE ARE HIGHLY SPECULATIVE! It is not
authoritative but is based on knowledge of the systems and hardware involved
as well as the photos of the explosion site.

The system: Nitrous oxide is used as the oxidized for the hybrid rocket
engine. Without going into a lot of detail, there are a number of good
reasons for using nitrous. One is that it is not a hazardous material in
that it is not poisonous nor corrosive. It is stored under high pressure,
however. At about 950 psi. At this pressure, it is a liquid at room
temperature and is self-pressurizing. That is, it tends to maintain a
constant pressure even as the tank is drained. This is a great advantage in
a hybrid rocket engine as it precludes the need for turbopumps to pump the
oxidizer into the engine or a pressurization system to keep the tank
pressurized.

The nitrous oxide is stored in a composite tank for the tests, usually
carbon fiber wrapped. There is nothing unusual about this. It is a
flight-rated tank. A conventional storage tank meant for ground use only
would be made from steel but there is nothing inherently flawed in using a
fiber-wrapped tank. NASA and the military use them all the time. But for
some reason, which is not yet known, apparently this tank exploded. Whether
this was the primary failure or was caused for some other reason is as of
yet unknown. Once released from confinement, the nitrous oxide liquid would
flash into vapor adding power to the blast similar to a steam boiler
explosion. Reports indicate a fire but the nitrous itself does not burn but
like pure oxygen causes any fire to burn more vigorously and intensely. As
nearly as can be discerned, two of the people on the site were killed
instantly from the concussion. A third died later, as I understand, from
concussion and shrapnel-like wounds. The remaining injured have similar
wounds, probably from the carbon-fiber tank debris which would be sharp and
deadly.

The hybrid rocket technology used by Scaled Composites for the Space Ship 1
and their newer design is inherently safer than solid or liquid engine
technology. Also, these people are professionals who don't take
irresponsible risks. Although the details are not yet known, we can assume
that this was an accident. Sometimes bad things happen to the most careful
and cautious people.

Our sincere condolences to the families and friends of those killed and
injured. We hope the injured recover quickly and completely. I know I sure
hope that the folks at Scaled Composites and Virgin Galactic also get on
their feet quickly and continue their important and exciting work. This is
indeed a sad day.