October 3, 2004 notes

 

X-Prize

 

I expect Scaled to complete their second X-Prize flight and claim the prize on Monday.  Good for them!

 

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 year’s 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 weren’t looking good, so we haven’t 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 wasn’t 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.  We’ll see if we have a 100km vehicle well tested by this time next year…

 

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.

 

 

Engine work

 

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.

 

http://media.armadilloaerospace.com/2004_10_03/drilledRetainer.jpg

 

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 gauge pressure

flameholding gap

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.

 

http://media.armadilloaerospace.com/2004_10_03/meltedDeflector.jpg

http://media.armadilloaerospace.com/2004_10_03/meltedThroat.jpg

 

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 didn’t 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 wasn’t 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 didn’t seem to effect the smoothness at all in the tests so far.

 

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.

 

http://media.armadilloaerospace.com/2004_10_03/heatExchanger.jpg (form http://www.exergyinc.com/ )

http://media.armadilloaerospace.com/2004_10_03/exchangerInjector.jpg

 

 

 

Vehicle work

 

We are building the top ends of both tanks – cone mounting flange, cone, lifting loop, GPS mount, tank top flange.

 

http://media.armadilloaerospace.com/2004_10_03/twinTanks.jpg

 

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 doesn’t 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 shouldn’t give us any trouble.  We worked out all the plumbing we need to add, and I have milled the proper holes today.

 

http://media.armadilloaerospace.com/2004_10_03/milledManway.jpg

 

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.

 

http://media.armadilloaerospace.com/2004_10_03/fullBase.jpg

 

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.