NASA’s OSIRIS-APEX spacecraft has successfully completed its closest solar pass, protected by innovative engineering solutions and showing improvements in onboard instruments. Credit: NASA Goddard Space Flight Center/CI Lab
OSIRIS-APEX, a NASA The spacecraft successfully made its closest approach to the Sun, exceeding design expectations and demonstrating robust engineering in protecting its sensitive components. Innovative techniques such as repositioning solar panels for protection allowed it to emerge unscathed, with subsequent testing revealing unexpected improvements to onboard instruments such as cameras and spectrometers. However, engineers remain cautious because the spacecraft must perform additional difficult perihelions to reach its target, the asteroid Apophis.
Mission engineers were confident that NASA’s OSIRIS-APEX (Origins, Spectral Interpretation, Resource Identification – Apophis Explorer) spacecraft could withstand its closest pass of the Sun on January 2, 2024. Their models predicted that, Despite traveling 25 million kilometers closer to the Sun than it was originally designed for, OSIRIS-APEX and its components would remain safe.
The mission team confirmed that the spacecraft indeed emerged from the experiment unscathed after downloading stored telemetry data in mid-March. The team also tested OSIRIS-APEX’s instruments in early April, once the spacecraft was far enough from the Sun to resume normal operations. Between December 2023 and March, OSIRIS-APEX was inactive, with only limited telemetry data available to the team on Earth.
Innovative engineering solutions
The spacecraft’s good health was down to creative engineering. Engineers placed OSIRIS-APEX in a fixed orientation relative to the Sun and repositioned one of its two solar arrays to protect the spacecraft’s most sensitive components during passage.
The spacecraft is in an elliptical orbit around the Sun that brings it to a point closest to the Sun, called perihelion, approximately every nine months. To take a trajectory that will allow it to encounter its new target Apophis in 2029, the spacecraft’s trajectory includes several perihelions that are closer to the Sun than the spacecraft’s components were initially designed for.
These two images from a camera called StowCam aboard OSIRIS-APEX show the same view taken six months apart, before (left) and after (right) the perihelion of January 2, 2024. Notably, it There is no observable difference on the spacecraft surfaces, indicating that the higher temperatures encountered at perihelion did not alter the spacecraft. Another insight gained from the identical view in both images is that camera performance was also not affected by perihelion. StowCam, a color imager, is one of three cameras comprising TAGCAMS (the Touch-and-Go Camera System), which is part of the OSIRIS-APEX guidance, navigation and control system. TAGCAMS was designed, built and tested by Malin Space Science Systems; Lockheed Martin integrated TAGCAMS into the OSIRIS-APEX spacecraft and operates TAGCAMS. Credit: NASA/University of Arizona/Lockheed Martin
“It’s phenomenal to see how well our spacecraft configuration has protected OSIRIS-APEX, so I’m really encouraged by this first close passage of perihelion,” said Ron Mink, mission systems engineer for OSIRIS-APEX, based at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. .
Unexpected benefits and ongoing challenges
In addition to confirming that January’s perihelion occurred as predicted, engineers discovered some surprises during testing of the spacecraft’s components. A few instruments performed better than expected after exposure to higher temperatures.
A camera that helped map the asteroid Bennu and will do the same on Apophis has seen a 70% reduction in “hot pixels” since April 13, 2023, the last time it was tested. Hot pixels, common in cameras widely used in space, appear as white dots in images when detectors accumulate exposure to high-energy radiation, primarily from our Sun.
“We think the heat from the Sun resets the pixels through annealing,” said OSIRIS-APEX project scientist Amy Simon, based at NASA Goddard. Annealing is a thermal process that can restore instrument functionality and is often done intentionally via built-in heaters on some spacecraft.
Captured on October 20, 2020, while NASA OSIRIS-REx The spacecraft collected a sample of the surface of the asteroid Bennu, this series of 82 images shows the field of view of the SamCam imager as the spacecraft approached and touched the surface of Bennu. OSIRIS-REx’s sampling head touched Bennu’s surface for approximately 6 seconds, after which the spacecraft performed a back burn. Credit: NASA/Goddard/University of Arizona
Another welcome surprise, Simon said, came from the spacecraft’s visible and near-infrared spectrometer. Before perihelion, the spectrometer, which has mapped the composition of Bennu’s surface, and will do the same at Apophis, appeared to have a Bennu rock stuck inside its calibration port. Scientists suspected that some sunlight could not filter through the instrument after the spacecraft, then called OSIRIS-REx, collected a sample from the asteroid Bennu on October 20, 2020. By picking up the sample then igniting its engines to move back from Bennu, the spacecraft stirred up the dust and stones that clung to it.
“But with enough maneuvering of the spacecraft and burning of the engine after sample collection,” Simon said, the rock in the calibration port appears to have been dislodged. Scientists will check the spectrometer again when OSIRIS-APEX passes near Earth on September 25, 2025, for a gravitational boost.
OSIRIS-APEX is now operating normally as it continues its journey to the asteroid Apophis for a rendezvous in 2029. Its better-than-expected performance during the first close perihelion is good news. But engineers caution that doesn’t mean it’s time to relax. OSIRIS-APEX must perform five more exceptionally close passes of the Sun – as well as three Earth gravity assists – to arrive at its destination. It is unclear how the cumulative effect of six perihelions located at a closer distance than expected will impact the spacecraft and its components.
The second OSIRIS-APEX perihelion is scheduled for September 1, 2024. The spacecraft will be 46.5 million kilometers from the Sun, about half the distance between Earth and the Sun, and well within the orbit of Venus.
