Flight Electronics Test
A brief update on the rocket engine test and tomorrow's upcoming flight electronics test.
On December 28th, 2018, Let's Build Rockets conducted cold and hot static engine tests.
The cold static test verifies that the plumbing of the LOX and fuel lines are operating as expected. In this test, we ran liquid oxygen (pressurized with helium) and water (instead of kerosene) through the system. The results of this test were nominal, allowing us to proceed to the hot tests.
We attempted three fires during the hot test, and encountered some issues. The first two did not ignite because the equipment was not sufficiently cooled. This caused the liquid oxygen to immediately boil off, entering the engine chamber as a gas rather than a liquid. In addition to this, we found that the LOX vent valve was frozen slightly open. Because the LOX was pressurized with helium, this meant we were leaking helium and any gaseous oxygen in the tank. The lost helium was the biggest problem here, because the leak was mostly helium, plus we had excess oxygen for the test anyways, and only a limited amount of helium.
The last hot test appeared to start correctly, after cooling the equipment more, but aborted at T+1. We reviewed the data and found that it tripped the "ignition failure" safety: that is, ignition should cause a spike in temperature, so after T = 0, the temperature should be very hot. If the temperature is below a certain threshold (100 C) then the computer assumes the ignition failed to occur and closes the fuel and oxygen valves. What actually happened, is between T=0 and T=1 we had ignition, but the effect of the LOX entering the engine chamber actually lowered the temperature below 100C before actually igniting and spiking up to 1000C. Unfortunately, the computer already detected the cold temperature and shut the valves, resulting in a burn of less than one second.By that point, our helium pressure dropped below operating pressure, so we couldn't fix that issue and conduct another test.
Further work on the engine has been postponed for now, and we are refocusing our efforts to complete the flight electronics, which needs to be completed by the end of the semester for Eric's senior capstone project.
Tomorrow, Saturday March 16th, 2019, we are planning on launching the current iteration of the flight electronics on a high power model rocket at the CATO launch in Durham, CT. For this test, we are testing three systems:
- The main flight electronics boards, which is responsible for flight controls and processing telemetry, will be launched with an altimeter, IMU, and GPS, and will report the data from these sensors along with system status through an ISM radio module. While this board is designed to do flight control for the LOX rocket, it will not be involved with the launch/engines at all on the model rocket.
- The recovery module, which transmits only GPS data over APRS. We will use this to recover the rocket from greater distances than the ISM module will be able to transmit, although this launch should not exceed communication distances of either module. There is an amplifier for the APRS transmitter that we plan to put on the LOX rocket, but will not be tested at this launch.
- The video module, which is an off the shelf video transmitter. It's designed for quadcopters/drones, but we are going to see how it works in rocketry applications. This transmits on an ISM band as well.
The launch is at White's Field, in Durham CT. Setup starts at 9AM, the rest of the event is 10am - 3pm.