December 16, 2007 update:
Im done sulking about not taking the Lunar Lander
Challenge, and we have been back at work for a while. (Insert your favorite motivational quotes
Matt is on a long vacation, so we dont have any pictures or
video to show, but here is what we have been working on:
We have finished a third module tank set, so we have two
modules bolted together and one single module test mule. We still have wiring and plumbing to do on
the duel module configuration, but there is a decent chance that we will try to
fly a dual module configuration in late January. A fourth tank set is going together now, so
the full four module configuration may be ready a month after that.
We are almost finished with our AFRL phase I SBIR, and we
are expecting to hear something in the next couple months about a possible
phase II. If we get that, we should be building
and flying an honest space vehicle in 2008.
Note that I am not saying that we would necessarily be all the way
through the test process to the point of flying to 100km, but we should be well
on the way. We have just gone through
all the grief about getting our accounting system and books in order for
government work, so there are some costs involved with going this way, but our technical
pitch to them is basically the path that we want to be following anyway, so if
they want to help out, we will work with them.
We are starting work for NASA involving flying our vehicles
on lox / methane instead of lox / ethanol.
We are going to initially just convert a module over in a fairly
straightforward manner, but our longer term goals involve using
self-pressurizing lox/methane combinations at very low tank and chamber
pressures for extremely high mass ratio upper stages. Depending on how our testing goes, methane
may or may not play a part in our booster strategy.
We still have several interesting commercial ventures in the
works, but so far, none of them have reached the point of anyone writing us any
The most important issue we have now is resolving the engine
start issues that sunk us at XPC 07. We looked
over all the data and parts as closely as we could, and we feel that there
might actually be two separate issues in play.
Clearly we are borderline in some ways, since
things work most of the time. We have
added a helium purge to the fuel manifold during the first second of the
startup sequence to prevent igniter heated gox from backflowing into the
cooling jacket, but we have some suspicion that we may have had the chamber
o-ring fail in some of these cases. The
possibility of trapped fuel between the injector and the chamber igniting
during the start sequence on a second flight is one thought, and excessive silicone
o-ring lube on a freshly assembled engine is another thought. We have the o-ring closer to the outer
diameter of the chamber, leaving a small shelf that can trap fuel, because our
current injector design had hot spots between
the spokes that burned o-rings that were closer to the inside diameter.
We are going to be trying a completely film cooled stainless
steel chamber soon. Completely removing
the cooling jacket removes any chance of anything exploding in it
We may have to use some combination of
increased film cooling, increased water content in the ethanol, reduced chamber
length, or even adding ethyl silicate to the fuel, but Im sure we can make
something work with it. Worst case, we
can include a graphite throat in a tapered stainless jacket. On the other hand, we may not need to detune
much at all. Our current design has
quite low coolant velocity, and it doesnt get all that hot. We might wind up with just an orange-hot
engine almost as-is. I was originally
thinking about sliding injectors in the way we currently do with the aluminum
jackets, but now I am thinking about just making stainless steel injectors and
welding the entire thing together. Much
as I hate machining stainless, there is something to be said for not having any
o-rings or retaining rings on the engine.
It is worth noting that lots of early French launch vehicles went all
the way to orbit with completely film cooled engines.
We are also still pursuing some improvements to our cooled
graphite engines. Simply cutting the
jacket volume in half may allow us to shorten our ignition cycle significantly
and make most of the issues we have go away.
I am concerned about the spokes in our current injector pattern
giving hot spots on the film cooled engine, so we made a test injector with one
of our current graphite chamber / jacket arrangements to try out a completely symmetric
pattern, as well as a new o-ring placement and assembly strategy (tighter
groove with no o-ring lube applied). We
had a brief flight with a smooth start (using the new purge-during-ignition
method), but the injector burned through fairly quickly due to a gox film in
the lox manifold. We thought this might
be a problem, as we had previously learned how critical it is that lox never be
allowed to circulate along the injector face.
Lox must always be distributed in a cool zone, then pushed essentially
straight down at the injector face. If
it ever flows along the face, it will quickly form a gas film and burn
through. On disassembly, we found that
the new o-ring was completely fine, which was a good sign.
We made a modified engine with a better lox distribution
manifold, and we intended to test it last weekend, but we ran into some startup
issues because the chamber pressure transducer had been cooked a bit by the
injector burn through on the previous flight.
It was still functioning, but it had enough noise in it that the igniter
safety interlocks kept tripping during startup attempts. We usually carry spare transducers, but we
didnt have one in the field that day, and it was really damn cold and windy,
so we just called it a day. Back at the
shop we replaced the transducer and made several improvements to the flight
control code to keep us from ever leaving the shop again with a transducer that
We have been doing some interesting machining lately with
integral AN fittings. I finally found a
37 degree tapered end mill, so we can now start with thicker pieces of metal
and carve everything away to leave fittings sticking out of manifolds, which
saves a fitting weld operation and leaves the fitting threads still in the T6
condition instead of annealed by welding.
There was some concern about sealing from a milled surface, but with a
careful cleanup pass it seems to work fine.