This weekend saw the inaugural testing of the Mk. IIB test platform. This is a static test system designed to allow us to test the thrust vectoring system that will be used on the Mk. V rocket, which is the one going to space. During testing, the nozzle ruptured, which made for some spectacular pictures. But we still got 5 seconds of perfect combustion data, and know how the nozzle failed, so we are ecstatic . So click through the pictures and check out what happened this weekend!
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Step 1: Preperations: Electronics
Before we packed up and went out to the test site, there was a lot of work to be done in the realm I oversee, ground support electronics. As I covered in early parts of this series, the ground support electronics (GSE) serve to both control the rocket and fueling system as well as serve as data acquisition. We had to finish integrating and implementing a few things in the software and Hyperion firmware, as well as do a dry run. The dry run consists of hooking everything up, and controlling everything manually as well as through the auto sequences to make sure everything is functioning. Then, do this process again. And again. With over 120 separate data and control lines, this process was surprisingly smooth.
Step 2: Preperations: Mk IIB
As well as set up and test the electronics. we had to also assemble the Mk. IIB. There were a few interference issues with the threaded rods, but they were sorted out quickly and easily; the Mk. IIB is designed to be super simple to modify, and is extremely overbuilt to ensure repeated safe testing. Once the Mk. IIB had been assembled, we ran multiple leak tests and dry runs with the electronics controlling all the valves.
Step 3: Setting Up the Test Site
The day of the test is finally here! We test at a disused sand quarry in Sudbury, Massachusetts for our static testing. We pile everything into a beat-up old pickup truck and a minivan (a Honda Odyssey we call '2014: A Space Odyssey' or 'Odyssey of the Stars'). Once there, we assemble the test stand, tip it upright on the mounting poles, and hook up the gas lines and cables. We didn't put on the combustion chamber right away, since we were doing a cold flow first, which is highlighted next.
Step 4: Test 1 and 2: Tank Drain and Cold Flow
These two tests were basically the same, and were run back to back. The first one was a tank drain, when the oxidizer tank was filled and then dumped without any additional pressure. This is to verify some of our models. Then, this was repeated with pressurant being pumped into the oxidizer tank to keep it at a constant pressure. This is called a cold flow, and it is the same as if the rocket ignited, but without the solid fuel and the flame. This too verifies our models and serves as a full system check. It is not as cool as the hot fire, which comes next
Step 5: Test 3: Hot Fire!!!
This is the fun part. We attach the combustion chamber and then ignite the rocket! We were going for a 10 second burn here, and made the burn duration despite the nozzle rupture, which produced some really cool fireworks. We got fantastic data, and have some solid analysis of the system performance on the next step. The horizontal load cells, which here hold the rocket vertical but later are going to be used for thrust vector testing, even measured the horizontal thrust created by the nozzle rupturing. But first, enjoy some videos!
Step 6: Test 4: Post Test Analysis
So, here are some nerd-a-licious numbers for those who are curious:
-Electronics worked!!!! We were stoked to have a brand new system function as well as it did the first time. When the nozzle ruptured, the servos for the thrust vectoring were damaged (obliterated) This shorted servo power to ground to servo PWM to servo feedback, which caused Hyperion to freak out and reset, but it was processing data and sending it back within a millisecond.
-We pulled about 152 pounds of thrust off our goal of 200. This is not fantastic, but for a first go 75% isn't bad for this rocket. The Mk. IIB was designed by the members of BURPG who haven't designed an engine before to serve as a learning experience. This is compared to the Mk. IV rocket at 99% of expected performance when designed by more experienced members. Our pressurant feed system didn't keep the rocket at the same pressure, so we are accounting the loss of thrust to this. You can see this in the video as the plume shrinks as the rocket burns.
-The nozzle ruptured due to a zero-thickness geometry on the convergent section of the nozzle (i.e., inside the combustion chamber, the part that funnels the gasses to the narrowest point of the nozzle, came to a point) This existed where the convergent section met the graphite throat. The sharp edge ablated (burned) faster, causing hot gasses to eventual leak around the graphite throat and burn through the steel nozzle casing. This is a very easy thing to fix, thankfully, and the Mk. IIB should be back up and running for next weekend.
-For those of you who were worried, the GoPro did survive. The lens was a little dirty, everything else was unscathed.
Well, that's a good start to the year! Next weekend we have some more testing scheduled, so check back to see how it turns out.