Almost unbelievably, I'm online for tonights launch of Phoenix. I couldn't
find the booster S/N.

Dang...it has no RocketCam. It's a bit of a surprise that I can still see
the plume itself after the airlit jettison. I could even see MECO from the
ground view replay, which is quite unusual (since it's about 600 miles away
from the lens.)

Delta II ascents are always one of my favorites, because the ascent
commentator is a real engineer and isn't afraid of explaining exactly how
this booster works. It might sound rather arcane compared to the commentary
of ascents with separate PAOs. I am also very familiar with the Delta II
and know exactly what he's talking about. Some things you might not know if
you don't watch an ascent of the Delta II:

- The solid motors on the first stage have a thrust curve. The commentator
lets us know this with phrases like "peak chamber pressure" and "solid
motors beginning to taper off". Check out some at www.thrustcurve.com (no,
the GEM-40's is not there.)
- The LOX tank's "top pressure", the pressure at the top of the tank, is
deliberately increased by helium injection near the end of the first stage.
I anticipated this as a need for the Ascent Lilmax booster, but this is the
first time I've noticed it on a real one. The reason for it is that most of
the net positive suction pressure (that pressure that keeps pumps from
cavitating) during ascent is provided by the weight of the liquid oxygen.
The weight of the liquid oxygen is not a result of Earth's gravity, but the
booster's accelleration. This weight drops very rapidly as the booster
depletes, and if you're not careful, you can have your engines shut down
early. The Delta IV Heavy (#310) had this embarassment on 21 December
2004. They fixed it obviously. (Also, the cavitation wasn't in the pumps
themselves, as they would have exploded.)
- The upper stage tanks are not supplied helium for their entire operation.
The helium runs out when the tanks are about 80% empty, and the stage
finishes its operation under blowdown pressure.
- The "CRD" translates into plain english as "bomb radio", or semi-plain
english as "Command Receiver/Decoder." The only real time command available
is to blow the booster up if it decides to be insubordinate. I haven't
heard of this happening since 1996; modern boosters are quite well behaved.

Right now, were in the coast, so ascent success is almost certain at this
point. The third stage systems are quite simple, and I'll introduce them on
my next post.

Terry


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