In response to their disappointing performance during the 2007 X-Prize Lunar Lander Challenge, Armadillo Aerospace has developed a new engine design. According to a news release on the Armadillo Aerospace Website, the big lesson from the X-Prize Cup last year was that their engine start sequence wasn’t reliable enough. The news release goes on to state, "One of the issues we were fighting with was that our cooling jacket held quite a bit of volume, so starting the engines at idle required a 1.6 second igniter operation time, and we ran into issues melting the igniter. We detuned the igniter to the point that it didn’t melt, but then we had some problems with reliable ignition. We believe there were also separate problems with pushing hot gox back into the filling cooling jacket, and also possibly an assembly problem on one of the engines.
We had plans of attack to resolve these issues with the regen cooled graphite chamber engine designs, involving reducing the jacket volume and adding purges during startup, but we decided to try another approach that might resolve it more definitively.
Making a chamber out of stainless steel and just adding extra film cooling has some significant benefits, although it is going to suffer some penalty in Isp. We had some data points from the radiatively cooled carbon reinforced graphite chambers that we were using in 2006. We had one engine that glowed orange hot before failing, but the engines that we flew at the 2006 XPC weren’t even glowing red hot on the outside after 90 second flights.
Once we have flown the four module system and convinced ourselves that it either works or doesn’t work, we will break the modules apart and start flying them higher and faster in Oklahoma. While we don’t have the permit in hand yet, it looks like AST has agreed in principle to let us fly our vehicles to 4000’ with our current safety systems. By light loading the vehicles and accelerating harder, we should be able to hit the same max-Q that our proposed suborbital vehicles will see, since we intentionally fly rather slow due to the wide, draggy nature of our modular vehicles. I expect we will wreck one or more of the modules in flight testing, but we have four of them, so it won’t be that big of a deal.
Once Spaceport America gets their final permit, we will take any remaining modules out there and see how high we can go. With the legs on, the modules don’t have a chance of getting to 100km, but if we learn all we need with normal flights, we might make a potentially-sacrificial flight of a module lifting off from a stand without legs. The landing wouldn’t be very pretty, but it might not be any worse than the return leg of our XPC flight last year.
Assuming the differential throttling works out on the four module system, our commercial vehicle plan is a six module triangular configuration with engines on the side between the tanks, using the base of the bottom spheres as landing pads. This configuration gives us full module-out redundancy, easy vehicle CG determination before launch, no landing gear weight, and it travels in flight orientation without a wide-load permit (just barely). For a cabin, we are going to use a 5’ diameter transparent sphere. "
