NASA engineers got their parachute wires crossed for OSIRIS-REx mission

'Inconsistent wiring label definitions' resulted in drogue being cut before it was deployed

NASA has revealed how a wiring mix-up resulted in a parachute problem on its otherwise successful OSIRIS-REx asteroid sample return mission.

The release triggers for the parachutes could have been wired incorrectly, resulting in the signals designed to trigger the drogue parachute – a small parachute used to provide some control and stability before the main parachute is deployed – being fired out of order.

This meant that rather than deploy at an altitude of 100,000 feet, the drogue actually deployed at 9,000 feet. Worse, the signal triggered the system to cut the drogue free while it was still in the capsule, meaning that it was immediately released when the drogue was deployed.

The main parachute deployed as expected and, fortunately for the scientists eagerly awaiting the samples of asteroid Bennu collected by the mission, it had enough redundancy in the design to both slow and stabilize the capsule for a safe landing. The upshot was that the landing took place more than a minute earlier than expected, but there was no negative impact to the sample.

The root cause looks to have been in the naming conventions used in the design. According to NASA, the word "main" was used inconsistently. On the signal side, "main" meant the main parachute. On the receiver side, "main" meant the pyrotechnic released the parachute canister for drogue deployment. Engineers simply connected the two mains, which resulted in the deployment actions occurring out of order.

NASA is no stranger to parachute malfunctions. In 2004, the sample return capsule of the Genesis probe crashed into a Utah desert after an acceleration sensor flaw resulted in the parachutes not being deployed. An investigation [PDF] revealed that the sensors had been upside down.

In this instance, the issue appears to have been down to a whoopsie caused by what the agency called "inconsistent wiring label definitions."

Still, the material liberated from Bennu was returned successfully, and the probe itself has headed off on a new mission to asteroid Apophis. Roughly 1,000 feet (305 meters) wide, Apophis is expected to come within 20,000 miles (32,186 km) of Earth in 2029. The probe – now renamed OSIRIS-APEX – will enter the orbit of Apophis and study how the encounter with Earth affects the trajectory of the asteroid, its spin rate, and its surface.

NASA now needs to look at the system responsible for releasing the parachutes. This is currently locked away with the Bennu sample, the processing of which remains the mission's top priority. Once done, engineers will be able to look at the hardware and confirm that a wiring error caused the parachute problem. ®

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