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automatic control of valves where timings are sched- uled with millisecond precision. To begin, valves sequentially open to mix fuel and oxygen in the igniter, a small chamber which shoots a flame into the main rocket engine. Following this, the PLC out- puts a 4-20mA signal to precisely command posi- tions of the main propellant valves with better than 1° of precision as they follow a pre-programmed pro- file to ensure smooth engine startup. Once the pro- pellants enter the engine’s combustion chamber they mix and are ignited by the igniter, which is then
shut off.
As the test reaches completion the main propel-
lant valves close and are followed by a sequence of valves automated to inject inert gas into the engine and surrounding area to clear any residual propel- lants and suppress any small fires. Closely tied with the normal valve and ignition functionality is the complementary auto-abort logic. The program is configured so any sensed anomaly will abort oper- ation, driving all valves closed and other devices to their safe state. The team has experienced engine startup sequences that were abnormal and the test was reliably shutdown each time by the PLC.
For each test run, all device status and instrument data are data logged to the PLC’s built in webserver. This allows quick, remote access of data for export
in CSV format after the run so the team can perform more detailed analytics using other PC-based soft- ware. Being able to remotely access the data from within the safety of a control bunker enables the team to efficiently run back to back engine tests.
Figure 4: Picture of live re.
The testing regimen progressed from dry cycling, to water tests, to ignition tests, to the nal live re operation. The automation system worked aw- lessly throughout.
3-2-1 Ignition
In 1961 as the Mercury Freedom 7 launch expe- rienced delays, an exasperated Alan Shepard is said to have barked “light this candle” to mission con- trol. However, any rocket program has extensive tests leading up to the proverbial candle lighting moment (Figure 4).
The UBC team members extensively and progres- sively tested their rocket engine test stand to ensure proper operation. Hundreds of test runs were per- formed, first operating dry to just exercise the controls and the equipment. Later the systems were operated with water so certain control and monitoring could be safely achieved without introducing propellants. Because reliable ignition is a must, the team next per- formed over 60 igniter tests before ever filling the sys- tem’s supply tanks with propellants. Finally, the team conducted a series of cryogenic checks where the liq- uid oxygen plumbing was tested with liquid nitrogen to ensure that all sensors and valves operated nomi- nally when exposed to cryogenic temperatures.
Eventually the team performed actual and com- plete live fire tests. As of this writing, there have been multiple fully operational test sessions, with five total firings. All systems and automation elements have operated consistently and as expected.
A Platform for the Future
Choosing and implementing commercially avail- able AutomationDirect PLC controls and instrumenta- tion enabled the UBC Rocket team to rapidly develop a reliable automation platform. It also gave them the ability to readily adapt the system to new and chang- ing requirements.
For instance, the team was able to progressively transition manual valves over to automatic valve con- trol. They also upgraded the propellant valves to pneumatic valve positioners, enabling them to throt- tle flowrates during key startup sequences. Currently the test stand is trailer-borne, but upcoming construc- tion phases are adapting the design to fit in a ship- ping container, with more automation for fire sup- pression and propellant filling.
UBC Rocket team members began the proj- ect with plenty of passion, but perhaps somewhat less hands-on experience. They were enthused to find how AutomationDirect systems and support
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Student Spotlight www.automationnotebook.com | Issue 43
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