NASA is set to redo hot-fire test of its central stage of the space launch system

Following a failed hot-shot test of the space launch system, NASA is likely to conduct a second “Green Run” fire in February.

On Tuesday, three days after the first hot fire test attempt, NASA released a summary of its preliminary analysis of the data from the 67.2 second test firing. The report highlights three issues, none of which seem too serious but which will require further investigation.

The agency found that the test, performed at the Stennis Space Center in Mississippi, was automatically stopped by an out-of-range reading of hydraulic pressure in the thrust vector control mechanism used to card or steer the engines. At 64 seconds from the test, the rocket began a pre-programmed sequence to card its engines as if it were in flight. Shortly thereafter, the pump’s return pressure fell below the red line of 50 pounds per gauge square, to 49.6. This pressure limit, the agency said, was stricter than an actual flight redline and was set to protect against potential damage on the test bench.

Another problem, the “major component failure” in engine 4, actually appears to be a relatively minor problem in which a redundant sensor has failed. That’s good, because it means NASA probably wouldn’t have to replace that main-stage engine. There are four main space shuttle engines used on the SLS rocket.

Finally, the “flash” observed in the engine part seems fairly normal. A visual inspection of the thermal blankets between the motors shows some burning, but this is normal. There was no indication of fire, leak or other problem.

To repeat or not to repeat?

The summary released by NASA does not discuss whether the agency will proceed with a second main stage test. Prior to the test, NASA had hoped to run the engines for at least 250 seconds to get a full suite of main stage performance data. Obviously, they only ran the engines for about a quarter of that time.

According to agency sources, program officials are in fact leaning toward conducting a second hot fire test in Mississippi. Due to the need to get more propellant at the test site, do a minor overhaul of the vehicle, and possibly change the 4 engine erratic sensor, the agency estimates that it will take around three to four weeks before having another test.

NASA and the main subcontractor of the main stage, Boeing, have collected a lot of data about the test. The agency said that of its 23 testing goals, 15 were met with 100% of the data sought. Four others got most of the data sought, while three had partial data and one had no data. (This was a test of the reaction of the liquid oxygen tank pressure when the liquid oxygen was largely depleted and the tank was emptied.)

NASA engineers are now studying the data in more detail and will soon be doing a risk assessment to determine the dangers of skipping a second test. As it is standard practice to retest under such circumstances, it is highly likely that a second test will occur.

It remains difficult to quantify what this means for the launch schedule for this key milestone in the Artemis I mission. Before this delay, NASA was already going to struggle to meet its goal of launching an unequipped Orion spacecraft. around the Moon before the end of 2021. There wasn’t much room left in the schedule, and a launch this year assumed smooth operations in stacking and integration – a big assumption. Now it seems likely that NASA will lose at least a month.