OSIRIS-REx Grabbed So Much of Bennu Its Sample Capsule Won't Fully Close
NASA says OSIRIS-REx collected so much asteroid material from Bennu that rocks are jamming its sample chamber door open.
Sometimes a mission fails by doing too well, and that’s basically what happened to OSIRIS-REx this week. Two days after its touch-and-go maneuver at asteroid Bennu on October 20, NASA is reporting a problem nobody was really worried about going in: the spacecraft’s sample collector grabbed so much material that it can’t close properly.
The TAGSAM head — the pogo-stick-like collection device on the end of the spacecraft’s robotic arm — was designed to briefly touch Bennu’s surface, fire a burst of nitrogen gas to kick up loose regolith, and capture whatever floated into its sample chamber. Based on images and telemetry coming back, it looks like the touchdown worked almost too effectively. Rocks and debris are apparently wedged into the mylar flap that’s supposed to seal the sample chamber, holding it partially open. Mission engineers have reportedly seen particles drifting away from the collector in images, which is exactly the scenario you don’t want when you’ve traveled this far to bring material home intact.
Why the plan changed on the fly
The original post-collection procedure called for a spin maneuver to measure the mass of collected material — basically spinning the spacecraft with the sample arm extended and using the change in rotational inertia to estimate how much regolith got scooped up. NASA has now skipped that step. Spinning a partially-open, material-shedding sample head sounds like a great way to fling away the very sample you’re trying to weigh, so the team made the call to skip measurement entirely and prioritize getting the material sealed away.
Instead, engineers moved up the stowage sequence, the process of retracting the arm and locking the sample capsule into the return vehicle for the trip back to Earth. That’s a significant change to execute this quickly after such a complex encounter, and it says something about how seriously the team is taking the leak risk.
If the sample stows successfully, this could end up being the largest extraterrestrial sample brought back to Earth since the Apollo lunar missions, an extraordinary outcome for a mission that only needed to collect 60 grams to be considered a success. There’s real irony in a spacecraft’s biggest problem being that it overachieved.
I’ll be watching for NASA’s updates on the stowage sequence over the next few days. Getting a sample chamber lid to seal around jammed rocks isn’t a trivial engineering problem, and there’s no fallback attempt in the current plan if it doesn’t go cleanly this time — Bennu is over 200 million miles away and the return window isn’t infinite. This is genuinely one of the more nail-biting moments of an already ambitious mission, and it’ll be worth checking back on before OSIRIS-REx begins its long cruise home.