Artist’s rendering of the Psyche spacecraft orbiting near the surface of the Psyche asteroid. Image: Maxar/ASU/Peter Rubin. NASA’s Psyche spacecraft, now scheduled for an October 12 launch, will reduce the power of its maneuvering system after engineers discovered that its engines could overheat during its eight-year expedition to explore the metallic asteroid.
The $1.2 billion mission came just two weeks into the launch window when a back-up engine was tested on a ground-based test bed for hotter-than-expected temperatures. Engineers at NASA’s Jet Propulsion Laboratory (JPL) initially suspected this was a separate problem with the testbed’s equipment, but it soon became clear that the thrusters installed on Psyche were also affected.
“The data that the subcontractor received about these cold gas thrusters was incorrect,” said Lindy Elkins-Tanton, Psyche’s principal investigator. The way the spacecraft operated was based on these specifications.
It could have been another major blow to the project, which has already been delayed for a year due to software delays, and has also faced challenges in designing and building the spacecraft during the COVID-19 pandemic.
When the piston problem was discovered, the Psyche spacecraft was nearing the end of pre-launch preparations at the AstroTech processing facility in Titusville, Florida, near the Kennedy Space Center. If any hardware changes were required, the mission could have missed its 20-day launch window and faced another major delay or even cancellation.
“It crossed my mind: Can’t we rest? Elkins-Tanton said.
However, it was quickly determined that overheating could be prevented by a fairly simple change in one of the parameters that control the pistons. Instead of operating at the planned 80 percent of maximum rated thrust, they would be limited to 30 percent.
“Thank God we have this great team,” Elkins-Tanton said. “I really moved to a place of total gratitude that they found it before we launched. And it was just a coincidence.
If the engineers hadn’t noticed the problem, the higher-than-expected temperatures could have damaged the propulsion units.
“It could have had a real impact on the mission,” Elkins-Tanton said.
The Psyche spacecraft is shown in a clean room as it prepares for launch. Image: Adam Bernstein/Spaceflight Now. Psyche’s 12 engines use nitrogen pulses to turn and steer the spacecraft. These so-called cold gas engines are a separate system from the xenon-powered ion engines that will propel the spacecraft on its journey into the asteroid belt.
Operating at a lower thrust level will mean the spacecraft will spin more slowly, for example when it’s pointing an antenna at Earth or aiming scientific instruments at an asteroid. The mission team ran simulations and tests to make sure the fix didn’t have any unintended consequences. NASA delayed Psyche’s launch for a week to complete testing.
“We’ve been working 24/7 and it looks like it’s going to work,” Elkins-Tanton said. “Right now, all the tests we’re doing — continuous, thousands of tests — have shown that 30 percent of us are fine.
Once all testing and validation is complete, the revised thrust setting will be included in the already scheduled pre-launch mission parameter update.
If all goes well, Psyche will be placed on two sides of the 43-foot-tall (13.1-meter) payload fairing on Tuesday, October 3. It will be transferred to Complex 39A at the Kennedy Space Center and docked with its SpaceX Falcon Heavy rocket on Monday, October 9.
Takeoff is scheduled for Thursday, October 12, at 10:16 a.m. EDT (1416 UTC). The mission has a chance to run every day until October 25th. inclusive, and after that in 2023 the launch window closes.
The Psyche mission will be the first to study a rare metallic asteroid, believed to be the remains of a protoplanet that was ripped to its core by a giant impact. The asteroid, officially named 16 Psyche, is irregular in shape, has an average diameter of about 140 miles (226 kilometers), and is composed mostly of nickel and iron metals. It is located in the outer part of the asteroid belt, which lies between the orbits of Mars and Jupiter. Arriving in the summer of 2029, the probe will orbit the asteroid for 26 months.