Then, a small drogue parachute was supposed to open to stabilize the 32-inch-wide (81-centimeter) sample return craft. About five minutes later, a larger main chute would open to slow the capsule for a gentle landing while protecting the precious asteroid material sealed inside.
At least, that was the plan. While OSIRIS-REx safely returned its asteroid sample to Earth, there were moments of high drama.
The capsule was supposed to send an automated signal to deploy the drogue chute at 100,000 feet, beginning a roughly five-minute timer before a second signal would cut a retention cord for the drogue, allowing the larger parachute to unfurl and complete the landing sequence. Instead, at 100,000 feet, the signal triggered the system to cut the drogue free while it was still packed inside the capsule, according to NASA.
At 9,000 feet, the other signal sent the command to actually release the drogue chute. But with its retention cord already cut, the drogue immediately released from the capsule, and the main parachute opened as expected.
"The first signal was supposed to fire the mortar and release the drogue," Lauretta said. "The second signal was supposed to cut the cable to release the main ... It looks like the first signal cut the (cable), and then the second signal fired the mortar, so it went backwards. But it worked. We had lots of margin on that main chute. It landed safely—a beautiful pinpoint landing in the Utah desert.”
An investigation by engineers from NASA and Lockheed Martin, which built the OSIRIS-REx spacecraft and sample return vehicle, found that build plans for the mission weren't specific enough in instructing technicians who assembled the return capsule.
"In the design plans for the system, the word 'main' was used inconsistently between the device that sends the electric signals, and the device that receives the signals," NASA said in a written statement. "On the signal side, 'main' meant the main parachute. In contrast, on the receiver side 'main' was used as a reference to a pyrotechnic that fires to release the parachute canister cover and deploy the drogue.
"Engineers connected the two mains, causing the parachute deployment actions to occur out of order," NASA said.
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