Faulty sensor may have canceled launch of NASA’s massive SLS rocket

NASA's SLS rocket could now launch on Saturday, September 3, 2022.
Enlarge / NASA’s SLS rocket could now launch on Saturday, September 3, 2022.

Trevor Mahlman

After wiping out an attempted launch from the Space Launch System rocket on Monday, NASA officials said they are working on a second attempted flight of the Artemis I mission on Saturday, September 3.

NASA flight controllers stopped the first launch attempt after being unable to verify that one of the SLS rocket’s four main engines, engine no. 3 – had been properly cooled to -420 degrees Fahrenheit prior to ignition. Engines must be cooled to very cold temperatures in order to handle the injection of very cold liquid hydrogen and oxygen.

During a Tuesday evening press conference, NASA program manager for the SLS rocket, John Honeycutt, said his engineering team believed the engine had actually cooled from room temperature to near the required level, but was not correctly measured by a faulty temperature sensor. .

“The way the sensor behaves doesn’t match the physics of the situation,” Honeycutt said.

The problem for NASA is that the sensor cannot be easily replaced and would most likely require a return to the Kennedy Space Center Vehicle Assembly Building in Florida, a few miles from the launch pad. That would delay the rocket’s launch until at least October, and the space agency is starting to worry about wear and tear on a rocket that’s now been stacked for nearly a year.

Honeycutt said he was convinced liquid hydrogen was leaking into engine no. 3 during Monday’s countdown and that other sensors, including pressure readings, indicated that the engine was in an environment that would have properly cooled it. Therefore, he said, his team is working on a “flight rational” plan that would allow the rocket to launch without getting good data from the temperature sensor on the engine.

“We will look at all the other data we have and [will] use it to make an informed decision,” he said.

As a result, NASA’s current plan involves work on the launch pad today, including inspecting an area where there was a small hydrogen leak during Monday’s countdown. Then, if officials are satisfied with those inspections and the rationale for their flight to address the faulty temperature sensor, the agency will begin the countdown on Thursday. On this timeline, refueling operations would begin Saturday morning, before the 2:17 p.m. ET (6:17 p.m. UTC) opening of a two-hour launch window. To give the launch team more time to work on the engine cooling issue, the process known as engine “conditioning” would begin earlier in the countdown than Monday.

At Tuesday’s press conference, it wasn’t immediately clear what the implications of launching with a hotter-than-normal main engine would be. From a physical standpoint, firing supercooled thrusters in a hotter-than-designed engine would likely cause severe damage to the RS-25 engine’s turbopump, at a minimum. It can therefore be assumed that NASA would not launch the SLS rocket without great confidence in its flight logic.

NASA has until September 5 to launch the booster before it must be removed from the pad for refurbishment. As the September 3 launch date approaches, the space agency will be closely monitoring weather forecasts in addition to handling technical issues. Although thunderstorms frequently develop along the Florida coast during summer afternoons, launch weather officer Mike Burger said the overland flow is expected to be quite strong this weekend. This should push the sea breeze further inland and potentially allow for some launch opportunities during the two hour window. If the weather negates the attempt, NASA is making arrangements to attempt a Sept. 5 launch.

Officials insisted at Tuesday’s press conference that they were confident to proceed with a launch attempt. Although the space agency heavily promoted the first Artemis I launch attempt on Monday – the launch of an uncrewed Orion spacecraft to the Moon was celebrated with celebrity appearances, social media promotion and a visit of Vice President Kamala Harris to the Florida Spaceport –NASA has yet to complete a refueling test of the vehicle.

Despite this, the space agency hopes to be able to fully fuel the rocket on Saturday and count to T-0 without further problems.

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