Ghost Circuit Breakers Spook NASA As Orion Heads Back To Earth

Ramish Zafar
Something's amiss in lunar orbit. Image: NASA

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After the Orion spacecraft entered its trajectory to Earth earlier today, National Aeronautics and Space Administration (NASA) officials shared more details about what lies ahead and the different issues the agency has encountered in the mission. Orion is slated to land in the Pacific Ocean on December 11th, and its return burn earlier today has set it on the path to landing. However, the landing site is yet to be chosen, and the space agency will select it later this week.

NASA Will Continue Testing Orion Spacecraft Even After It Lands In the Pacific Ocean

Today marks the 20th day of the Artemis 1 mission, and the highlight of the day was the return-powered flyby burn which placed the spacecraft on its way back to Earth after reaching 80 miles of the lunar surface. Now that the road is set for Orion, NASA will continue testing it to gather more data for future crewed flights. The next mission in the Artemis program is Artemis 2, which will see a crew fly around the Moon on a different trajectory than the current mission.

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The Orion's journey around the Moon is over for now, and it will now seek to complete landing objectives for a splashdown in the Pacific. As it headed home, NASA tested its auxiliary engines for longer burn times to meet future mission parameters. Throughout Artemis 1, teams fired these engines for 17 seconds, but the tests fired them for longer durations to assess the impact on the solar panels.

These tests were successful, and they saw temperatures within ten degrees. NASA also tested the heaters for the propellant and water lines to match Artemis 2 requirements to discover that up to 90 Watts of power savings were delivered, explained the Orion program deputy manager Debbie Korth.

The return path for Orion on Earth. Image: NASA

As it returns to Earth, the spaceship will continue to undergo more tests. According to Ms. Korth, these include a 'solar array wing modal survey' repeat test. This was previously conducted during the mission, and it tests the arrays for degradation. Engineers will test the arrays again to check if any structural or other changes have occurred since they have been stressed during the distant retrograde orbit and the lunar journey to gain an idea for future missions. Other tests include the propellant system valves being checked for leaks after the lunar journey to enable NASA to develop a flight profile for future missions.

A key problem that has confused the engineers is the power system onboard Orion. Some tests included tweaking the ship's service module's power control distribution unit (PCDU). This receives power from the solar arrays and distributes it through feeders to the different systems, such as the flight control and reaction control thrusters.

NASA divided the eight feeders into two groups of four, and one of these groups tripped. This led to the propulsion systems going into standby, which led to six out of the twelve auxiliary thrusters on Orion going into standby as well. Generally, these current limiters trip when a command is sent, but this time they went off on their own accord, with no command present on record to open the current limiters.

Orion's reentry profile as it 'jumps' on the atmosphere before landing. Image: NASA

NASA's Artemis 1 mission manager Michael Sarafin described the problem as follows:

In your house, a light switch or a circuit breaker, that is the command device. You literally flip the switch and it closes the circuit, and that is the action or command that does it. What is a little bit odd to us is there is no record of a controller on board the vehicle sending a command to open the latching current limiter. So, in your house, the device is the command object; in this case there is a separate controller that tells the current limiter to open or close. And there is no record of the command device saying you should open or you should close. This thing is just open or closing without this box, the command device, telling it to do so. So there is some anomalous behavior that we are trying to understand.

Orion will renter the Earth at an altitude of 400,000 feet while traveling at roughly 24,529 miles per hour. The 'jump' will take place a little over seven minutes later at 291,382 feet at 16,824 miles per hour to slow it down to the speed at which a spacecraft generally enters from low Earth orbit. Its speed will slow to 528 miles per hour at 50,000 feet, and the forward bay cover will be jettisoned at 22,845 feet at 285 miles per hour. The main parachutes will deploy at 5,320 feet, with splashdown at 20 miles per hour.

Testing won't end there, though, as NASA will keep Orion for two hours after splashdown to study heat dissipation. This is the 'resident' heat within the spaceship, and the test will let the teams determine the ship's cabin temperature profile. This will test the heat that soaks back into the vehicle even as the ocean and the heat shield have cooled it. Additionally, as it enters the atmosphere, Orion's reaction control thrusters will be fired at different points to gain more insights into flight thermal profiles at hypersonic speeds. Orion uses 11 parachutes to reduce its speed for splashdown.

NASA will select the landing site for the Orion spacecraft will be selected on Thursday, and the ship will land off the San Diego coast in the Pacific Ocean on December 11th. After the landing, NASA aims to fly Artemis 2 in 2024, and the mission will test the life support system and proximity docking technologies.

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