Testing an engine bound for space indeed is rocket science
HOUSTON — Rob Morehead snaked a camera on a cable up the rocket engine’s nozzle looking for anomalies caused during the combustion of supercold liquid oxygen and liquid methane.
He ran his fingers along the inside of the nozzle — which previously had been heated to 1,800 degrees — feeling for areas of burnt metal or for sooty remnants.
Soot is a sign of incomplete combustion, a wasted opportunity to produce more thrust.
The camera found one small spot of erosion. His fingers were soot-free. The engine passed its inspection.
“I think we’re ready to continue,” Morehead said as the crew members hiked back to their camp chairs and canopy a safe 300 feet away at Ellington Airport.
Houston-based Intuitive Machines is building a nearly 13-foottall lunar lander, the Nova-C, that’s set to deliver commercial cargo and NASA-provided payloads to the moon in the fourth quarter of 2021.
The 102-person company was founded in 2013 by two former NASA employees and the former CEO of a company that provided engineering services to NASA.
NASA is relying on commercially built lunar landers, such as the Nova-C, to deliver science and technology demonstrations to the moon.
These efforts support the agency’s Artemis program, which seeks to return humans to the moon and develop a more sustainable presence there.
To keep costs low and iterate quickly, Intuitive Machines is building portions of its rocket engine with a 3D printer and then testing it in Houston.
That means every week or two, its team of engineers and technicians drives the engine loaded on a flatbed truck (called
the mobile test stand) and tows a command trailer to an abandoned taxiway at Ellington Airport.
Grass grows between the cracks, except for an area the team mowed for safety reasons, and the engine’s roar mixes with F-16 fighter aircraft, T-38 NASA jets and AH-64 Apache helicopters that frequent the airport.
Earlier this month, on the company’s 38th rocket engine test day, Intuitive Machines was assessing a modified injector design that could help keep the engine cooler.
The injector is a showerheadlike device that has tiny holes in intricate patterns to spray liquid oxygen and liquid methane, allowing them to combine and be ignited.
The engineers and technicians arrived at Ellington about 7:30 a.m. and began unloading, setting up cameras to film the tests and connecting ethernet cables to run data from the flatbed truck to the command trailer, where monitors display the temperature and pressure of various engine components.
They checked the safety system that would detect a methane leak or unintended fire.
“The fire coming out of the back is OK,” project manager Greg Vajdos said. “Any other fire is not good.”
Then they did other pretest tasks, such as checking for leaks, and worked out a few sensor and wiring issues.
A high-pitched noise floated down the taxiway as they pressurized the propellant tanks prior to testing. They sent negative-300-degree liquid oxygen and negative-260-de
gree liquid methane through the valves, engine plumbing and injector to cool these components to a temperature more like space.
Clouds of mist surrounded the engine as the supercold liquids chilled the exposed metal, condensing the humid air nearby.
Then Morehead, the senior propulsion engineer, led the countdown. The engine ignited for two sec
onds at 10:51 a.m.
“We always start with a short test,” propulsion engineer Matt Atwell said. “Make sure the start looks good before we go to longer tests.”
The second engine firing lasted four seconds at 10:56 a.m. The third test was just shy of six seconds at 11:04 a.m., cut off early when a sensor met the conservative 1,800-degree temperature threshold.
Running at full capacity, the engine turns cherry red and gets almost hot enough to melt.
The team tests these limits on some days to ensure the engine will withstand the rigors of space. But during this test of the modified injector, Morehead limited how fast the engine warmed to protect the hardware from damage.
The computer was programmed to shut off the engine should it reach a conservative temperature, like 1,800 degrees. When it reached that threshold, the team made a few adjustments and ignited the engine again, watching and collecting data as a blue flame shot out of the mobile test stand.
Candles and campfires burn yellow as soot contacts the air. The engine has a blue flame due to its high temperature and lack of soot.
After the team inspected its handiwork, crew members ate lunch and continued running tests.
Ultimately, the main engine was ignited 15 times with durations up to 20 seconds.
The team members also performed three ignitions of the main engine igniter (a small oxygen/methane rocket that lights the main engine) in a vacuum chamber at temperatures below negative 200 degrees, which simulates the worstcase conditions for lighting the main engine.
“We want to make sure that when we get into orbit, we’ve covered all our bases for all the bad things that could happen to us,” Morehead said.
To do this, they’ve spent hundreds of hours testing and many hot summer days at the airport.
There will be more tests to come, all in preparation for the engine’s 15 minutes of flame — the time required for three engine ignitions that will guide the lander to the lunar surface.