NASA’s efforts to snag a piece of asteroid on Tuesday may have worked a little too well. The OSIRIS-REX spaceship has packed so much stone and dirt that some of the material is now being returned to space.
The operation about 200 million miles from Earth on the other side of the sun was “almost too successful,” said Dante Lauretta, the mission’s chief investigator, during a telephone press conference Friday. NASA officials feared that without careful efforts to secure its samples in the coming days, the mission could lose much of the scientific payload it had transported across the solar system for years to collect them.
A few stones caught in the robotic probe’s collection mechanism prevented a flap from closing completely. In images captured by the spaceship, scientists could see pieces of asteroid coming out. Dr. Lauretta estimated that each picture showed about 5 to 10 grams – up to about a third of an ounce – of material floating around the collector. This is a significant loss as the goal of the mission is to bring back at least 60 grams of asteroid debris and stones.
“You have to remember that the whole system is in microgravity,” said Dr. Lauretta. The particles move like in a liquid, “and particles kind of diffuse out,” he said.
However, the visual evidence suggests that the spaceship collected much more than 60 grams. Thomas Zurbuchen, associate administrator for science, said NASA had decided to make preparations for stowing the sample. “Time is of the essence,” he said.
If the acquisition attempt had not been successful, OSIRIS-REX could have made two more attempts.
Mission managers also decided to abandon two maneuvers. One planned for Friday was to slow the spacecraft down and put it back into orbit around the asteroid Bennu, which is only about 1,600 feet in diameter. Instead, it continues to drift at less than a mile per hour.
The second was to turn the spaceship around on Saturday to measure how much is trapped in the collection mechanism. But that would shake more material. “So this is not a prudent way,” said Dr. Lauretta.
The collection of a sample was the primary objective of the mission, the full name of which is Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer. Asteroids are primitive 4.5 billion year old remains from the earliest days of the solar system. Scientists on Earth using sophisticated instruments could study the Bennu material in much more detail than any of the instruments on the spaceship.
On Tuesday, the spacecraft’s collection mechanism touched the asteroid Bennu at a leisurely pace of about 1.5 inches per second. The sampling mechanism, which is similar to an automotive air filter, is designed for a variety of surfaces ranging from completely stiff – “like walking into a concrete slab,” said Dr. Lauretta – ranging to something much more porous.
It turned out that this part of Bennu was a little softer and the asteroid barely pushed back. The sampling mechanism pushed 10 to 20 inches into the ground before the spaceship retreated, allowing it to fill its collector when a burst of nitrogen gas from the probe kicked up the surface.
“We couldn’t have done a better collection experiment,” said Dr. Lauretta.
The process of stowing the collection mechanism can begin on Tuesday. Engineers are considering how the process can be changed to minimize the amount of material that can be shaken into space. It takes a few days for samples to be safely stored in a return capsule.
OSIRIS-REX will have to wait until March to leave Bennu and return to Earth, a journey that will take two and a half years. The spaceship will deliver the return capsule, which will launch for a landing in Utah on September 24, 2023.
OSIRIS-REX is the third mission attempting to bring back parts of an asteroid. A Japanese mission, Hayabusa, faced a series of technical glitches and barely succeeded in bringing back samples – about 1,500 grains – from an asteroid it was studying, called Itokawa. The Japanese space agency sent a second mission, Hayabusa2, to another asteroid, Ryugu. This spaceship is on its way back to Earth and will drop its asteroid payload in the Australian outback in December.