A detailed analysis of the descent video and capsule documentation led NASA to discover that discrepancies in wiring label definitions in the design plans likely caused the mix-up in the parachute release triggers. This confusion led to an out-of-sequence deployment of the drogue chute.
The drogue was supposed to deploy at approximately 30,480 meters (100,000 feet) to slow and stabilize the capsule during its roughly five-minute descent, before the main parachute opened at around 3,048 meters (10,000 feet).
However, at 30,480 meters, the system erroneously cut the drogue free while still packed. At 2,743 meters (9,000 feet), the drogue deployed but was immediately released from the capsule due to the prematurely cut retention cord.
Fortunately, the main parachute deployed as designed, stabilizing and slowing the capsule for a safe landing, which occurred over a minute earlier than planned. The Bennu sample was unharmed by the unexpected drogue deployment.
The root cause was traced back to the inconsistent use of the term "main" in the design plans. On the signal side, "main" referred to the main parachute, while on the receiver side, it indicated a pyrotechnic for releasing the parachute canister cover and deploying the drogue. This led to the incorrect wiring of the two mains, resulting in the parachutes deploying out of order.
NASA plans to test the parachute release system to confirm the cause. The hardware is currently housed with the Bennu sample at NASA's Johnson Space Center in Houston. Once the sample material is processed - a priority for the mission - NASA engineers will have access to the parachute hardware for verification.
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