Within the design and building phase of a rocket or spacecraft it is critically important to test the entire vehicle on the ground. After all it is important to ensure your stages will seperate and the engines will light before you try and fail at 10,000 feet. What follows is the initial log of my attempt to Static Fire Solid Rocket Motors for the Asteria I.
Day One of Ground Based Testing Log:
I built the static fire test stand today. It is fairly simple in design. Just a block of wood with engine sized holes in it to aim the engine upwards, with a smaller hole to let the ejection charge gasses escape. And all of it is held down by cinder blocks. Underneath is an Iron shovel to redirect the hot ejection charge gasses sideways. It is basically my own mini version of the NASA Stennis Space Center test firing range. I still need a name for it though. With the light fading I slipped two A8-3 engines into the stand. These are the smallest engines I have and my goal was to simply test simultaneous ignition. I hooked them up (see the photos) and fired the charge to ignite them and…. Nothing. I tried for a few moments and still nothing. I tried switching to an alternate power source and still nothing at all. With the light mere minutes from gone I decided to call it a night and packed up our electronics and engines leaving the test stand behind.
Day Two of Ground Based Testing Log:
Today I got going fairly bright and early. I got out an electric current tester and tested the current on my igniter boxes. I put in a new battery and quickly burned out a fuse on my 1994 Multimeter. Oops. With the fuse replaced I decided it was getting power and put the ignitor on my small grabber. I pushed the button and sent power down it and low and behold in my magnifying glass I saw the telltale sign of the ignitor turn from black to gray. It worked! Now it was time to take this to the test stand and try it out for real. So yet again I went out to the test pad. I set up my cameras to take slow motion footage and got ready to fire. I hit the button and again nothing happened. After trying again and again I eventually gave up and called it for the day.
Day Three of Ground Based Testing Log:
Today, the last day of the long weekend, I figured it was my last chance to get a good test in before the week started and I likely wouldn’t have any chances. So this time I made some changes. Instead of hooking the ignitor directly to a battery or ignitor box I hooked it to a car battery charger and…. https://youtu.be/axB6QMH4BfA It worked! The slow motion camera caught a lot of really cool things I had never known about (see review section below). I set up two more engines and tried firing them but it didn’t work. Looks like we need more power. I removed one of the engines to set up a single fire to ensure your system was still working and yet again… https://youtu.be/P6fEJciTPJA It worked once again! As the snowstorm was really picking up I decided to head inside and call it a day until I could acquire a system that had more power.
So finally after 3 days of work I managed to get my Static Fire to work twice. After reviewing the footage from above I learned multiple crucial things which I intend to use my knowledge of to help both myself for the rest of this study and into the future, as well as sharing with others what I have learned. I have already posted both of my slow motion videos to Reddit in multiple rocketry forums in an attempt to assist others and help them learn what I found without seeing it happen the hard way. So what follows is my findings. I hope it can help all of us into Rocketry and Aerospace:
Number One: Ejection charges are not what everyone normally expects.
Most people who think of a Parachute Ejection charge that happens a few seconds (usually 6 or 8) after MECO, think that it comes in the form of a jet upwards much like the initial thrust. At least that is what I thought until we did this testing. After seeing what really happens it is more of a jet of flame then a powerful compact column of thrust. It quickly turns into a fireball before fizzling out. This explains why you use wadding because it gets hit by the fireball and pushed upwards releasing the nose cone and parachute while also burning off. By the time it releases fully there isn’t that much wadding left as it has all burned. This also explains why if you put too little wadding it starts to use the parachute as wadding and burns up the chute a bit. So that is something very nice to know and something I am going to need to consider in the final design. I can also use this fact in the designing of my separation system between stages and with the pod.
Number Two: Ignition can be a bit harder than you think.
Everyone thinks that the actual flight is the hardest part. But just getting the thing off the pad is clearly going to be a challenge. Good electronics and GSE (Ground system equipment) is going to be key. There isn’t a ton more to say on this but frankly I’m starting to see why major space systems have so many issues and scrubs due to GSE. Infrastructure is going to be important.
I am sure with time and with more fires I will discover things I don’t know yet but that is in the future. For now I leave you to have an amazing day and fly high!