OSIRIS-REx illustration
An illustration of NASA's OSIRIS-REx spacecraft, with its sampling arm extended, approaching the surface of the asteroid Bennu. Credit: NASA/GSFC/Univ. of Arizona

WASHINGTON — A NASA mission to return samples from one near Earth asteroid will get an extended mission to visit a second asteroid under a plan approved by the agency April 25.

NASA announced that the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, or OSIRIS-REx, spacecraft, on its way back to Earth after collecting samples from the asteroid Bennu, will travel to the asteroid Apophis after returning samples in September 2023.

The main spacecraft, after ejecting the sample return container that will land in the Utah desert, will fly by Earth on a trajectory that will bring it to Apophis in 2029, shortly after that asteroid passes just 32,000 kilometers from the Earth. The spacecraft will spend 18 months in the vicinity of Apophis, studying the 350-meter asteroid and coming close enough to use its thrusters to brush away surface rocks and expose subsurface materials.

Apophis has long been an asteroid of interest to planetary scientists because of its close approaches to Earth in 2029 and 2036 that, for a time after its discovery, raised concerns about an impact. While scientists have ruled out an impact, the close approach offered the prospect of spacecraft missions to study the asteroid, something the OSIRIS-REx mission team had been discussing since 2020.

“Apophis is one of the most infamous asteroids,” said Dani DellaGiustina, deputy principal investigator for OSIRIS-REx, in a statement. She will become principal investigator of the extended mission, called OSIRIS-APEX for “Apophis Explorer,” after the Bennu samples are returned to Earth. “We were stoked to find out the mission was extended.”

Scientists will use the extended mission to study the composition of the asteroid as well as determine if the asteroid’s structure was affected by the close Earth flyby. The project estimates the extended mission will cost $200 million over nine years.

“The investigation is not without substantial technical risk,” Lori Glaze, director of NASA’s planetary science division, wrote in an April 25 memo approving the extension. The trajectory OSIRIS-APEX will take will bring it within half an astronomical unit of the sun, much closer than originally designed when the spacecraft traveled to Bennu, requiring what she called “significant engineering work” to ensue spacecraft systems can survive several such close approaches before arriving at Apophis.

OSIRIS-REx was one of eight planetary science missions that won extensions after a “senior review” of spacecraft that had already completed their primary missions. NASA extended the other seven missions — Curiosity, InSight, Lunar Reconnaissance Orbiter, Mars Odyssey, Mars Reconnaissance Orbiter, MAVEN and New Horizons — by three years each.

NASA extended the InSight Mars lander despite expectations that declining output from its solar arrays will cause the mission to end later this year, before the extended mission can begin. A report from the panel that conducted the senior review noted the project gives the spacecraft only a 5% chance of surviving through the end of this year, with the expectation that, by December, power levels drop to a level called “dead bus recovery” (DBR) mode that render the spacecraft inoperable.

The extended mission, though, would allow the possibility for some spacecraft operations if the spacecraft can revive itself in the next Martian summer in mid-2023. “If the spacecraft can ‘resurrect’ itself from DBR after depth of winter,” the report stated, “system operability would need to be determined at the time” to see if an extended mission was feasible.

NASA is also closely monitoring fuel levels on Mars Odyssey, a spacecraft operating at more for more than two decades. The overall spacecraft is “remarkably healthy,” the senior review report stated, but uncertainty about how much fuel is left on the spacecraft raises questions about how long it can continue to operate to both conduct science and serve as a communications relay for other Mars missions.

Other than OSIRIS-REx, NASA did not disclose the cost of extended missions. NASA’s fiscal year 2023 budget proposal projected spending between $7.8 million, on InSight, and $45 million, on the Curiosity Mars rover that year. Glaze wrote in her memo that for New Horizons, projected to spend $12.5 million in 2023, she would look to share costs with the agency’s astrophysics and heliophysics divisions because of the science that distant spacecraft would perform in its extended mission.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...