Did you ever, when you were little, get an Erector Set, or a really cool set of Legos or Constructs for Christmas? Do you remember how that felt, and what the living room floor looked like shortly after you got that box in your giddy fingers? Well, that’s how it’s felt here at Masten Space Systems over the past several days. In this case though it appears that Santa Claus lives in Indiana…

Erector Sets for the Young at Heart
As I mentioned last time, we had ordered in most of the major structural items for the propulsion bay section of our XA-0.1 vehicle. Almost all of the pieces are in now, and we’ve put together the framework:

The frame is mostly aluminum extrusions held together with bolted joining plates. The landing gear Y-frames are welded steel, done by a Blaine Fabrication of Sunnyvale, with industrial shock absorbers attached. We’re still waiting on the footpads, and then we’ll have the legs powder coat painted, but otherwise the structure and landing gear is put together now. The structure for the propellant bay and the avionics bay should be in the next few days. With luck we should have the footpads back and welded together, the landing gear painted, the LOX tank insulated, both tanks mounted, and be partway into the plumbing by the next time we post.

Engines, Electronics, and Coding Oh My…
We’re now up to 63 firings on our XVT-500LIT series of engines, and we’re getting close to moving onto our third generation chamber. The first one was a watercooled semi-heat-sink design, the second one was a part regen, part heat-sink design, and this third generation should be our first full regen version. The first two have taught us a lot of useful things about chamber layout, joint design, igniter and sensor design, as well as establishing throttleability and some basic performance numbers for the engine. We’ll need to run a few more firings to verify our performance numbers, and we still want to do some more partial throttle and L* tests, but we have enough data to move on to our third generation engine as soon as we have it in-house.

The goal of this next engine is to resolve the thermal issues so we can have an engine good enough for multiple ~30s firings without damage. We’re not absolutely positive that we can get this specific design iteration to steady state at full throttle and ideal mixture ratio, but if we can’t, we should be able to get close enough for longer duration firings and to get the rest of the thermal data we need for a final, flight engine. We’re hoping to get that engine on our test stand this weekend or early next week.

But so far, everything is looking pretty good. We’ve been able to throttle down stably to at least 40%, and have been able to acheive the design thrust levels at the chamber pressures specified. We’re not positive what the Isp/c* efficiency numbers are yet (which is why we want to run a few more tests on the 2nd generation engine), but what we have is more than good enough to start flying with once we have the cooling issue pinned down.

One of the other things we’re working on now is figuring out how to adequately package the whole engine, TVC system, throttle valves, and all associated electronic controls into a single module (that fits inside the triangular frames you can see in the pictures above. Since we really didn’t want to deal with rotary seals, particularly load bearing, high pressure, cryogenic rotary seals, our engine module is likely going to end up looking like some sort of squid-like monstor by the time we’re done with it. But it should be sufficiently modular by the time we’re done with it that all you have to do to swap one in or out is to disconnect two or so cables, a few bolts, and 4 fluid connections. That should make maintenance a lot easier, and will make upgrading the propulsion bay section to the XA-0.2 configuration much easier (the propellant bay section will probably be trickier to upgrade, but c’est la vie).

In addition to the engine itself, the two TVC systems are now mostly assembled, and some test code has been written and tried out on them. We still want to run them using the actual engine microcontroller code once Pierce is done with that, but the actual hardware side of both of the demonstrators is ready for the Battle of the Actuators. Both of these systems are quite strong, and very fast. It should be quite a show.

Here’s Pierce’s system:

And here’s Ian’s:

Speaking of code, there is one benefit to being the only guy in the company without a computer software/IT background–I don’t get stuck with any of the coding work. The good news is that those who are stuck with that unenviable task are going about it in a sufficiently systematic way that it at least gives me warm fuzzies. One of the nice things about our build-a-little, test-a-little approach is that since most of our XA-0.1 flights will take place dangling on a tether under a Grade-All or similar device, the implications of a code bug aren’t quite so bad as if this were say an orbital vehicle like Falcon I. We still need to be careful, but there’s a whole lot to be said for a system that can be gradually checked out, step-by-step. We’ll probably do some sort of ultra-formal critical design review at some point (bringing in a hostile outside review team to go over our whole design with a fine-toothed comb), probably before we go to build the XA-1.0, but by that time we should have had a chance to actually test all the concepts and subsystems, and debug most of the code ourselves.

So, all in all things are coming along fairly well here. I should hopefully have some more bloggy goodness next week or so.