A Web Around Asteroid Bennu – Transcript
This is Bennu…
One of Earth’s closest planetary neighbors…
An asteroid roughly the height of a skyscraper…
A remnant from the dawn of the solar system, made of carbon-rich rocks and boulders…
And since late 2018, the place that NASA’s OSIRIS-REx mission has called home.
When OSIRIS-REx arrived, it began wrapping Bennu in a complex web of observations – starting with a Preliminary Survey of its size, shape, mass, and spin.
On New Year’s Eve, OSIRIS-REx was captured into orbit by Bennu’s miniscule gravity, making it the smallest world ever to be orbited by a spacecraft.
In early 2019, it broke orbit to conduct a Detailed Survey.
A series of sweeping passes allowed OSIRIS-REx to study geological features at different latitudes and times of day, enabling stereo imaging and landmark-based navigation.
During the Detailed Survey, OSIRIS-REx globally mapped Bennu at only 5cm per pixel – the highest-resolution of any planetary body…including Earth.
On June 12, the spacecraft entered a new orbit at an altitude of just 680 meters – setting another record, and establishing a home orbit for the remainder of the mission.
In September, it began Reconnaissance on four candidate sample collection sites: potential locations on Bennu to touch down and collect a sample later in the mission.
OSIRIS-REx concluded its first year at Bennu back in orbit, circling the asteroid’s terminator, or boundary between day and night.
Here, outside forces acting on the spacecraft are balanced, allowing it to orbit within the same plane over time.
Reconnaissance resumed in early 2020, with close flyovers of the primary sample collection site Nightingale, and the backup site Osprey.
In mid-April, OSIRIS-REx performed the first of two rehearsals prior to sample collection.
It navigated to a predetermined “Checkpoint” about 125 meters above Bennu, then descended to within 65 meters before backing away.
After the Checkpoint rehearsal, OSIRIS-REx flew one final Reconnaissance sortie over site Osprey.
Then, it made a series of high-altitude maneuvers while rebooting its onboard processor, and preparing for its second rehearsal of the sample collection event.
On August 11, OSIRIS-REx departed its home orbit and made a four-hour traverse to Bennu’s northern hemisphere, retracing its earlier path.
After performing the Checkpoint engine burn to begin its descent, it made a second engine burn called “Matchpoint” to match Bennu’s rotation, before backing away at an altitude of approximately 40 meters.
Now, the most crucial moment of the mission had arrived.
On October 20, 2020, at approximately 11:30 am Mountain Time, the spacecraft departed orbit.
A few hours before, mission controllers on Earth had sent the commands for the Touch-And-Go sample collection maneuver, or TAG.
As they watched with anticipation, OSIRIS-REx steered itself to sample site Nightingale, maneuvering toward the small crater at the walking pace of a spider.
At 4:11 pm, the mission received confirmation: OSIRIS-REx had touched down and collected its sample.
Following TAG, the spacecraft drifted to a safe distance away from Bennu.
By the end of October, mission controllers determined that it had exceeded its goal of collecting 60 grams of asteroid material.
They directed it to stow the sample in preparation for return to Earth.
Before departing Bennu, OSIRIS-REx was given one final task.
On April 7, it flew over site Nightingale to observe how the sample collection event had changed the surface.
And with that, OSIRIS-REx had recorded its mark on Bennu and spun the last strand of its web.
In September 2023, the spacecraft will fly past Earth and send its sample home.