It’s been several months since our last update, and while this one will probably be a bit more brief than usual, I figured it was a good time to catch everyone up on what Masten Space Systems has been up to over the past several months.
The weekend before we left for the X-Prize Cup, we tried our first set of dynamic throttle tests, in the hopes that we could have that sufficiently debugged to demonstrate dynamic throttling for the crowd at Las Cruces. We had a weird issue with very low frequency combustion instability that we couldn’t figure out that night, so instead of risking not having something ready for the show, we converted the trailer back to the old static-throttling configuration for the X-Prize Cup. There at the X-Prize Cup, we had a great series of firings, with the longest one peaking out at 94 seconds of picture perfect hot flamey stuff. The only issue we had the whole week was one firing where the heat-soak after the firing warmed one of the igniter solenoids to the point where we weren’t able to do an immediate relight as we had originally planned.
After getting back to Mojave, we started noticing that the igniter was progressively getting more and more flakey with overheating, so we decided to spend some time fixing that. We had made a minor change to our PLC code prior to X-Prize Cup to shut the igniter GOX off after the engine had lit, in order to conserve GOX for long firings. It turns out that it looks like that change resulted in damaging the GOX orifice, which had then caused the whole igniter to run just on the lean side of stoichiometric, at much higher pressures than it was designed for, so it was overheating.
We fixed that, and got back to testing. However, on one of the tests, we recreated (this time in broad daylight) the same series of events that caused our hard-start back in August. Fortunately, we caught things just in time to prevent the engine from punting itself again. This time we had all the data, and the surprising result was that the igniter had fired, and the LOX and IPA had both entered the chamber, but the igniter hadn’t properly lit the engine. We think this is what really happened back in August, not some mystery LOX valve jam that magically unjammed itself. Anyhow, we went back to the igniter cart, and figured out the problem. It turned out that with the settings we had selected, it was possible to get a very weak flame while still triggering the ignition detect. We duplicated the problem on the igniter cart, and then found a fix that we verified would work consistently. Now that we know what to look for, we were able to devise a test to make sure it never happens again. Our percentage of false negatives will probably go up, but false positives shouldn’t be a problem any more. In the process of solving the problem, we made the igniter a lot more roudy. The flame is now consistently something like 6-8 inches long. Randall Clague was over while we were doing one of the tests, and he thought we were firing an RCS engine. While we were doing these modifications, we also made some fixes that greatly reduced the overheating problems. Also the engine’s startup transient is a lot smoother now than it ever was in the past. So we think we’ve improved both the ignition system, and more important the ignition detection interlock.
After sorting out all the annoying igniter problems, we also figured out what was causing the bizarre low-frequency instabillity we saw in our first attemtps at dynamic throttling. We wanted to check the angle vs Cv callibrations to verify that we were getting consistent valves from Flometrics, so we rigged up a flow-test stand. I was watching the visual flowmeter when Ian turned it on, and sure enough, the float was bobbing up and down at exactly the same frequency as the instabillity. We ended up doing some various electrical fixes, including some grounding work, some signal filtering, and a few other things, and in the end we stamped the instabillity out completely.
We then started doing dynamic throttle testing, to determine a throttle map for the engines. Pierce had overhauled our Labview Daq setup, and Dave had made a vehicle control GUI to run the engine computer in the same manner as it would function on the vehicle. It ended up taking a couple of days to get all the data we needed, but by a week before Christmas, we had succesfully wrapped up our engine development program. The engines are now working robustly, the ignition is functioning correctly, the engine computer is working very reliably, the valve control scheme is now complete, and the dynamic throttling is so smooth that it’s almost freaky.
Vehicle Hold-Down Testing
With the engine development work wrapped up, we decided to proceed on to vehicle hold-down testing, in preparation for our upcoming first flight. We welded up a steel Hold-Down Stand to place the vehicle on, with the goal of keeping the engines away from the ground for long-duration hold-down firings. Our next-door neighbors at the test site are the AirLaunch/Protoflight guys, and they helped us place the vehicle on the stand using their high-lift right before Christmas. After getting back, we went through finishing up the last couple of leak checks, electrical checks, and other tests we wanted to do before firing the engine for the first time.
We also decided to fabricate a cheap flame deflector so we wouldn’t damage the Hold-Down Stand or dig a pit next to it during testing. The deflector was made out of three laminated layers of douglass fir 2×4′s. We knew that people have had some success using wood as an ablative in the past, and with a total materials cost of about $12, we figured it was worth trying out.
After catching and fixing some initial electrical wiring problems on the vehicle itself, we went out today and fired an engine on the vehicle for the first time. It was absolutely amazing! We had three firings, one was just about half a second, the second one three seconds, and the last one somewhere between 10-12 seconds (by my reckoning). The first two firings barely did anything to the flame deflector, but the top layer of wood was burned through in a couple of spots after the long duration run. The good news is that the vehicle, the hold-down stand, and the flame deflector all worked exactly as expected, and the sacrificial layer on the flame deflector should only cost about $4-5 and about a couple of minutes to replace.
Here’s a video:
One of the big reasons things have been going slower lately is that we’ve been trying to transition over from living off of investment money to actually bringing in enough revenue to become cashflow positive. After the X-Prize Cup, apparently due to the impressive show we put on, we had almost half a dozen companies and individuals approach us about licensing technology, or doing engine or vehicle development projects. So, we’ve been spending a lot of our time over the past few months trying to hammer out deals with one or more of those entities. I can’t give any details until the deals are actually signed and the customers have given permission (and then it will probably be in the form of a formal press release), but things are moving along in that direction.
Now that we’ve had a few succesful static firings on the vehicle, we’re going to work on dynamic throttling, and eventually dynamic throttling and simultaneous gimballing on the vehicle with one engine. After that we’re going to take it apart for thorough inspection, and then order in the valve motors and other parts to get the other three engines completely assembled and on the vehicle. Depending on how quickly and smoothly that goes, we’ll probably do some multi-engine hold-down tests later this month or early next month. We want to make sure that we aren’t getting any weird cross-coupling going on before we actually try flight testing. Once we have the multi-engine hold-down tests done, we’ll integrate the ACS computer from Frontier and get this vehicle in the air under its own power.