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NASA’s effort to grab a piece of an asteroid on Tuesday may have worked too well. The spacecraft, OSIRIS-REX, grabbed so much rock and dirt that some of the material is now leaking into space.
The operation some 200 million miles from Earth on the other side of the sun was “almost too successful,” Dante Lauretta, the mission’s principal investigator, said during a telephone news conference on Friday. NASA officials were concerned that without a careful effort to secure its samples in the coming days, the mission could lose much of the scientific payload that it traveled for years through the solar system to collect.
Some rocks wedged into the robotic probe’s harvesting mechanism prevented a flap from closing completely. In the images taken by the spacecraft, the scientists were able to see fragments of asteroids emerging. Dr. Lauretta estimated that each image showed between 5 and 10 grams, up to about a third of an ounce, of material floating around the collector. That’s a significant loss since the mission’s goal is to recover at least 60 grams of asteroid soil and rocks.
“You have to remember that the whole system is in microgravity,” said Dr. Lauretta. The particles are moving like in a fluid, “and the particles are diffusing,” he said.
However, visual evidence suggests that the spacecraft collected much more than 60 grams. Thomas Zurbuchen, associate administrator for science, said NASA has decided to begin preparations to store the sample. “Time is of the essence,” he said.
If the harvest attempt had not been successful, OSIRIS-REX could have made two more attempts.
The mission managers also decided to cancel two maneuvers. One, scheduled for Friday, was to slow the spacecraft down and allow it to re-enter orbit around the asteroid Bennu, which is only about 500 meters in diameter. Instead, it continues to drift away at a speed of less than a mile per hour.
The second was spinning the spacecraft on Saturday to measure how much is trapped within the harvesting mechanism. But that would bring out more material. “So that’s not a wise path to take,” said Dr. Lauretta.
Collecting a sample was the key objective of the mission whose full name is Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer. Asteroids are 4.5 billion-year-old primitive remnants from the early days of the solar system. Scientists on Earth using sophisticated instruments could study Bennu’s material in much more detail than any instrument on the spacecraft.
On Tuesday, the spacecraft’s pickup mechanism touched the asteroid Bennu at a leisurely rate of about 1.5 inches per second. The sampling mechanism, which resembles a car air filter, had been designed to work on a wide variety of surfaces ranging from completely rigid – “Like hitting a concrete slab,” said Dr. Lauretta – even something much more porous.
That part of Bennu turned out to be smoother, and the asteroid barely recoiled. The sampling mechanism pushed 10 to 20 inches into the ground before the spacecraft recoiled, allowing it to fill its manifold when an explosion of nitrogen gas from the probe stirred the surface.
“We couldn’t have done a better harvesting experiment,” said Dr. Lauretta.
The operation to stow the collection mechanism can begin on Tuesday. Engineers are studying how to modify the procedure to minimize the amount of material that can be tossed into space. It will take several days for the samples to be safely stored in a return capsule.
OSIRIS-REX must wait until March to leave Bennu and return to Earth, a journey that will take two and a half years. The spacecraft will leave the return capsule, which will parachute to a landing in Utah on September 24, 2023.
OSIRIS-REX is the third mission that attempts to recover pieces from an asteroid. A Japanese mission, Hayabusa, faced a series of technical failures and barely managed to bring back samples (about 1,500 grains) from an asteroid it was studying called Itokawa. The Japanese space agency sent a second mission, Hayabusa2, to a different asteroid, Ryugu. That spacecraft is on its way back to Earth and will drop its asteroid payload in the Australian outback in December.
