October 3, 2004 notes
I expect Scaled to complete their second X-Prize flight and
claim the prize on Monday. Good for
We gave up our last glimmer of hope to have a vehicle ready after
the August 8 test flight crash. The
only stacked-miracles path that could have worked was to have perfect test
flights at SWRS with the 48 vehicle, then build out the 63 diameter carbon
fiber vehicle and have perfect test flights with it, then get some combination
of influential senators and popular support leaning on AST and WSMR to fast
track our launch license and launch site work.
Not a very likely scenario.
Realistically, we fell out of the running when we had to
give up on 90% peroxide due to the lack of availability. All the mixed-monoprop engine development
caused us to go a full year without a test flight. The critical error was letting X-L Space Systems close shop,
thinking that we would be able to deal with FMC. If I had acted as a steady anchor customer for them I would have
had to store a full years worth of peroxide production before our consumption
rate reached their minimal output rate, which would have required significant
storage tank facilities and looked like a lot of money to lay out two years ago. Bad call, at least for the time-critical
X-Prize. The mixed monoprop may yet be
a better propellant for manned suborbital flights for several reasons, but
the development has stretched on quite a bit.
We recognized a year ago that the odds werent looking good,
so we havent pushed on the launch license and launch site work, because both
of those are likely to get easier in the next year or two, and it wasnt worth
spending the time and money on them without a good shot at the X-Prize payoff.
With a few better decisions early on, maybe another day a
week of work, and about a million dollars more thrown at the site and license
problem, we probably could have done it this year. Well see if we have a 100km vehicle well tested by this time
We have basically returned to the development plan we were
pursuing before the X-Prize got funded.
The 48 diameter vehicles are a nice size to be working with, relatively
inexpensive, capable of going supersonic (at high tank pressures), and capable
of carrying a single passenger if we choose.
We will continue working at this vehicle size under our burn time waiver
without a launch license until one of the commercial spaceports gets the
necessary environmental work done for VTVL vehicles.
We did some more tests with the gas bubble smoothing
phenomenon. Adding accumulators did
help, but not as much as bubbling the gas in.
We are confident enough that we can make something work that we went
ahead and assembled the new 12 engine.
The new 12 engine has a drilled retaining plate on both
ends of the hot pack, so no there is no area for screens to burn away and let
rings slip out.
The build order for the motor is (bottom to top):
½ thick drilled retaining plate side welded to tube
1.5 kg of rings
8 mesh screen, ½ thick water jet cut support plate, 8 mesh
screen, welded under 6000 psi gauge pressure
1.5 kg of rings
¼ thick drilled retaining plate, welded under 6000 psi
½ thick water jet cut support plate
2 x 8 mesh screens
2 thick 900 cpsi monolith
10 x 20 mesh screens
1688 x 0.032 hole spreading plate
domed top with protruding 1.5 feed pipe to leave a
compressible air gap at the top
We did some runs with the uncooled chamber under the new
preburner injector. The heating
behavior was strange the chamber sides never glowed red hot, even though we
melted through our blast deflector and part of the chamber throat.
I think I have a good theory to explain all three observed
behaviors the chamber heating up brightly over the entire surface on one
configuration, with splotchy heating on another, and with only nozzle heating
on this one. When we have sonic choked
flow from the preburner, it goes sonic at the preburner throat, then separates as
a column and heads almost straight down without expanding into the rest of the
chamber and giving the methanol sufficient time to burn. Our very first couple runs didnt have
choked flow, so the subsonic preburner exhaust spread into the entire
chamber. After we shrank down the
preburner throat to get a bigger pressure drop and full choking we got
basically straight shots out of the preburner, but the combination of the ratty
hole saw cut for the throat and the not-exactly-centered and extension welded
fuel tube in the middle caused a lot of stray directional flow at sonic
velocity. The new injector has a
perfectly clean tube for the preburner throat, and the methanol is injected
annularly, so we got an almost non-diverging straight shot going down the
center of the chamber, but because it wasnt perfectly aligned, it chewed up
one side of the throat plate.
I think the lesson is that if we want to choke the
preburner, we need to slam the exhaust into some kind of a splash plate to make
it subsonic again. That might be
difficult to cool, so we may well just increase the throat diameter and let it
run unchoked, which didnt seem to effect the smoothness at all in the tests so
We are also exploring another option, replacing the
preburner with a heat exchanger, so the ambient temperature methanol vaporizes
the LOX without actually burning anything.
This may still give us a throttleable engine without all the extra
controls the preburner needs.
(form http://www.exergyinc.com/ )
We are building the top ends of both tanks cone mounting
flange, cone, lifting loop, GPS mount, tank top flange.
The milled manway arrived, it had been held up in a
warehouse for a couple weeks. We had previously
been using the flat composite manway cover that came with the tanks, but going
to a solid aluminum one gives several advantages: It is a little lighter (37 lb vs 45 lb, but I could have made it
a lot lighter if I wanted to thin out the flange), we can weld directly on it, the
sides are flat to support equipment shelves, and it doesnt need a thin
aluminum plate between the cover and the propellant, which forced us to use a
1/8 o-ring that was rather problematic.
The new cover has a ¼ o-ring groove that shouldnt give us any
trouble. We worked out all the plumbing
we need to add, and I have milled the proper holes today.
The jet vane / landing gear assembly is almost finished. The jet vanes are Rene-41, but we welded
them to 316 shafts using R-41 filler.
If we have any problems with the shafts, we can go to R-41 for them, but
we will have to bore out all the graphalloy bearings slightly. Once the engine is fully welded together and
we have the manway plumbing done, we can weld up the support struts that go
from the shock absorbers to the manway cover.
Our repaired differential pressure transducer finally
shipped, so we should be able to test our fuel guage with the full manway
plumbing next week. We are probably
going to be held up on our new custom electronics, but everything else should
be good to go on one vehicle in two weeks.