GOTS transportation fixture Avionics checkout
When we listed our risks for the test, we thought we’d been thorough in enumerating and mitigating them: leaks in the feed system, loss of communication with the stage, over pressure failure of the chamber, oxygen cleanliness, etc. What we didn’t expect at all was for our gas cylinder order to get lost… After a day of running around south Georgia on Tuesday, we were finally able to locate the methane, oxygen, and nitrogen we needed and arrange for delivery again down in Eastman. Another day of uncooperative weather (rain and 35 degrees) made for a bit more frustration on Wednesday, but we took the time to conduct the chamber pressure test, water jacket pressure test, cooling system tests, cold flow tests, and calibrate our test stand instrumentation.
Final engine components Load cell calibration
Test site setup on a cold, rainy day Chamber pressure testing – 400 psi N2
On Thursday, we prepped for the first of two hot fire test we planned to complete: a short duration (5 seconds), low pressure (75 psi) firing. This test served as a dry run of nominal and off nominal procedures for the full firing to be completed on Friday including notification of air traffic, tank purge and fill, feed system purge, and the ignition system. Additionally, the short duration burn allowed us to verify the performance of the test stand, instrumentation, water cooling system, as well as the stage itself. The stage propellant tanks were filled to 500 psi, for the first time allowing us to run the test completely from the fully integrated stage itself rather than ground support equipment. Confirmation of ignition was accomplished visually such that the test sequence would be automatically aborted if the igniter failed (which it did the first few times due to miswiring of the transformer) With the power system issue resolved, the test proceeded.
As you can see in the video above, we had a slight hard start with propellants igniting downstream of the nozzle exit, but overall still a successful test. We saw almost no throat erosion, nor any signs of the aluminum chamber exceeding its material or thermal limits. Looking at the data, we were satisfied and ready to progress to the full duration, full pressure burn.
The 15 second burn was run at full pressure – 2,000 psi stage tank storage pressure, regulated to 750 psi on both O2 and CH4 branches. Looks like there was an amount of asymmetric erosion of the aluminum, water-cooled throat which caused the plume to deviate from the centerline during the last five seconds of the test. Preliminary indications point to ablation of the brass chamber pressure transducer port, causing increased heating to one side of the chamber’s converging section. We’re reducing data from video footage, load cells on the test stand and pressure transducers throughout the stage over the next few weeks to clarify exactly what happened over the course of the burn, as well as quantify the performance of the propulsion system in terms of thrust and specific impulse.
More updates to come as we complete post-test analysis and move on to the next iteration of the GO Transfer Stage.