NASA will make a second attempt to launch the agency’s giant Space Launch System rocket on Saturday on a test flight to send an unmanned Orion crew capsule around the moon and back, a major milestone in the agency..
Due to problems cooling one of the rocket’s four shuttle-era engines to the required temperature prior to launch, executives said Tuesday’s engineers came up with a workaround. Assuming the final clearance proceeds, the launch team will begin a new countdown at 4:07 PM EDT on Thursday.
This will set the stage foron the Artemis 1 mission at 2:17 pm on Saturday, one day after the launch date of the original NASA backup. As always, the team will have to work around time, with forecasters predicting a 60% chance of stormy conditions during the rocket’s two-hour launch window.
Mike Sarafin, president of NASA’s mission management team, said the center stage refueling procedure will be changed in an effort to improve the cooling of all four RS-25 engines. Additionally, the fittings will be tightened around a fuel line umbilical at the base of the rocket to improve sealing and prevent leaks like the one that briefly occurred on Monday.
“We agreed on what was called ‘option 1’, which consisted of operationally changing the (fuel) loading procedure and starting engine cooling first,” said Sarafin. “We also agreed to do some pad work to address the leak we saw at the umbilical of the tail hydrogen service shaft.
“And we have also decided to move our launch date to Saturday. We will reconvene the mission management team on Thursday to review our flight logic and our overall readiness.”
The 322-foot, 5.75-million-pound tall SLS is thenever built by NASA, generating 8.8 million pounds of takeoff thrust using four Aerojet Rocketdyne RS-25 engines left over from the shuttle program and two Northrop Grumman solid rocket thrusters attached to a Boeing-built central stage.
Accelerating to 70 mph – upward – in just seven seconds, the solid rocket thrusters and center stage will augment the Orion capsule, carrying instrumented test dummies and a suite of sensors and experiments, into an elliptical orbit. The rocket’s upper stage, provided by the United Launch Alliance, will then push the capsule out of Earth’s gravity and onto a trajectory toward the moon.
After a close flyby, the capsule will circle the moon and move into a distant orbit that will take it farther from Earth than any man-made classified spacecraft. Then, after another lunar flyby, the ship will return to Earth for landing in the Pacific Ocean west of San Diego on October 11.
The goal of the Artemis 1 mission is to test the SLS rocket and the Orion spacecraft, including a high-speed, high-temperature reentry, before launching four astronauts around the moon in late 2024. The firstit is planned for the period 2025-26.
Given the ever-changing positions of the Earth and the Moon, coupled with the rocket’s ability to reach the correct trajectory, NASA must launch the Artemis 1 mission within specific “windows”.
To complicate the picture, the battery used by the upper-stage self-destruct system has to be serviced after 25 days, and this can only be done in NASA’s Vehicle Assembly Building.
This means that the Artemis 1 mission must take off by Monday or the rocket will be returned to the VAB, delaying another launch attempt no earlier than the end of September or, more likely, until October.
The SLS rocket is the key to the Artemis program, and NASA’s managers and engineers want to make sure it works as intended before launching astronauts to the moon.
On March 18, 2021, an eight-minute full-duration main stage engine test was performed at the Stennis Space Center in Mississippi. The rocket was then shipped to Kennedy Space Center for launch processing.
NASA carried out a general rehearsal countdown and refueling test on April 3, a critical milestone needed to make sure the rocket, launch pad, and ground systems work together as intended. But the engineers ran into a number of mostly ground system problems that prevented them from loading propellants,
Two other refueling attempts failed on April 4 and 14 due to a number of unrelated problems. Engineers were finally able to fully charge the main stage on June 20, but only after a leaky quick release fitting was insulated which prevented the flow of hydrogen coolant to the main stage engines, a requirement for a launch. actual.
The quick release was repaired in the Vehicle Assembly Building and the SLS rocket was returned to Pad 39B on August 16 to prepare the vehicle for launch.
During the launch attempt on Monday, the fixed quick disconnect appeared to be working normally. With the middle stage tanks filled and refilled, liquid oxygen and hydrogen began circulating through the engine’s hydraulics to condition them to the ultra-low temperatures of the propellants: minus 423 degrees Fahrenheit for hydrogen and minus 297 degrees for oxygen. .
But none of the engines reached the target temperature. Engines 1, 2 and 4 came in at around -410 degrees while engine No. 3 only reached about -380 degrees. During troubleshooting, the engineers diverted all hydrogen coolant to engine 3 and it still hasn’t reached its planned operating temperature.
John Honeycutt, SLS program manager at Marshall Spaceflight Center, said engineers suspect a faulty sensor may be responsible for engine 3 readings. Pressure measurements and other data indicate good cooling.
“The way the sensor behaves is not in line with the physics of the situation,” he said. “And then we’ll look at all the other data we need to use it to make an informed decision on whether or not we’ve cooled all the engines.”
By starting the cooling procedure about 45 minutes earlier, when the motors are close to ambient temperature, the engineers believe they can cool all four motors as needed.
A similar procedure was used during the rocket’s test launch last year at the Stennis Space Center. If so, the engines have been properly cooled and started normally for a “green run” for the duration.
“To date, and based on the data we have, we think we can do something similar to what we did at the Stennis Space Center to put ourselves in a better position for launch,” said Honeycutt.
As Sarafin said, the team will review all data on Thursday before giving final clearance to proceed with a launch attempt.
“The team is carefully examining the data and building the logic of flight,” Honeycutt said. “I don’t have it yet, but I expect we’ll be able to get there.”
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