How OSIRIS-REx sampled Bennu with gas: an illustrative 3D explainer

Illustrative, not to scale. Generic schematic of OSIRIS-REx's Touch-And-Go Sample Acquisition Mechanism. Shapes, positions, proportions and motion are illustrative, without a physical scale. This is not a reconstruction of the flight hardware.

The diagram and all explanations work without 3D.

Read the steps below to follow the intended function.

Component descriptions are below.

Motion is illustrative; speeds, particle amounts and travel are not measurements. In 3D: drag to rotate; on touch screens, use two fingers to rotate and zoom, one to scroll the page. Mouse wheel scrolls the page.

Intended function — not a flight replay

Hold the head out
The arm extends, flexing at its shoulder, elbow and wrist, to hold the head out from the spacecraft before contact.
Sources: The OSIRIS-REx Spacecraft and the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) (2018) · NASA: TAGSAM Testing Complete: OSIRIS-REx Prepared to TAG an Asteroid
Touch the surface
The head meets the ground and the pads on its rim touch it. Sensors that declare contact start the gas release.
Sources: The OSIRIS-REx Spacecraft and the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) (2018)
Release nitrogen
Gas from one bottle flows down a feed line to the head and into the ground. Moving dots represent the idea, not a measured flow.
Sources: The OSIRIS-REx Spacecraft and the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) (2018) · NASA: TAGSAM Testing Complete: OSIRIS-REx Prepared to TAG an Asteroid
Catch material and back away
Like wind blowing sand, the gas carries loose material up into the head, where the screen lets the gas out. About five seconds after the gas release, the spacecraft backs away.
Sources: The OSIRIS-REx Spacecraft and the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) (2018) · NASA: TAGSAM Testing Complete: OSIRIS-REx Prepared to TAG an Asteroid

What happened at Bennu

On 20 October 2020 the head touched Bennu at about 10 cm per second; the gas fired after about 1 second of contact, and the spacecraft began backing away after about 6 seconds. Images indicated that rocks held the head's Mylar flap open and material was escaping, so NASA sped up stowage; the arm placed the head in the return capsule by the evening of 27 October. NASA reports 121.6 grams of Bennu material delivered to Earth on 24 September 2023. This was sample collection for science, not resource extraction.

Sources: Near-zero cohesion and loose packing of Bennu's near subsurface revealed by spacecraft contact (2022) · NASA: OSIRIS-REx Goes for Early Stow of Asteroid Sample · NASA: OSIRIS-REx Successfully Stows Sample of Asteroid Bennu · NASA: OSIRIS-REx Bulk Sample Mass

Limits of the result. The ground gave way more than the design expected: the head had sunk about 6 to 7 cm before the gas fired, and NASA says the spacecraft would have sunk into Bennu had it not fired its thrusters to back away. The schematic shows the designed sequence, not that response.

Sources: Near-zero cohesion and loose packing of Bennu's near subsurface revealed by spacecraft contact (2022) · NASA: Asteroid Bennu Reveals Its Surface Is Like a Plastic Ball Pit

Like wind blowing sand, the gas mobilizes surface material, carrying it into the collection volume.

Sources: The OSIRIS-REx Spacecraft and the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) (2018)

What each part does

Arm: An articulated arm with a shoulder, an elbow at half its length and a wrist holds the head away from the spacecraft; NASA gives its length as 3.35 m (11 ft). A spring in it was designed to soften contact; at Bennu it was never compressed. Sources: The OSIRIS-REx Spacecraft and the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) (2018) · NASA: TAGSAM Testing Complete: OSIRIS-REx Prepared to TAG an Asteroid · Near-zero cohesion and loose packing of Bennu's near subsurface revealed by spacecraft contact (2022)
Nitrogen bottles: Three high-pressure nitrogen bottles, released separately, allowed up to three sampling attempts. A 2022 study says they were attached to the arm between the spacecraft and the head; their exact place here is illustrative. Sources: The OSIRIS-REx Spacecraft and the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) (2018) · Near-zero cohesion and loose packing of Bennu's near subsurface revealed by spacecraft contact (2022)
Sampler head: A round head about 30 cm wide, shaped like a brimmed hat: gas enters the ground through an opening at the brim, and a screen around the collection chamber lets the gas out while keeping the material in. Sources: The OSIRIS-REx Spacecraft and the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) (2018) · NASA: TAGSAM Testing Complete: OSIRIS-REx Prepared to TAG an Asteroid · NASA APOD: Tagging Bennu (2020)
Contact pads: Twenty-four pads of metal Velcro around the rim of the contact surface were designed to collect material they touched. Sources: The OSIRIS-REx Spacecraft and the Touch-and-Go Sample Acquisition Mechanism (TAGSAM) (2018)

What the schematic leaves out

Arm segment lengths, joint ranges, the head's height, where the bottles sit, the flap's shape and the pads' size are not established by this schematic. Inspect the sources for the design, and the linked mission record for its recorded outcome.

OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) · Compare the three mechanisms in 3D · Explore PlanetVac · Explore TRIDENT · Bennu's sample site before and after, in 3D · How MOXIE made oxygen · Compare what each demonstrated

Sources behind this explanation

Source-based explanation; viewing it does not recheck or change the mission record.