The Rite of Invoking (降ろしの儀 Oroshi no Gi) is what the Immortal Ship Committee chose to call accessing the data present in Ochiai's brain. Involving the use of Ochiai's clone (who had Ochiai's brain implanted within him 100 years prior), it was an intense procedure that required the approval of the committee.
The first time this event occurs is when the pacifist group within Sidonia demands to access knowledge on terraforming. Terraforming was part of the knowledge Ochiai destroyed and stored within his auxiliary brain.
The Rite of Invoking requires that Ochiai's brain be awakened, including his personality. While his clone's memories remain sealed off to him, Ochiai's ego returns during this event, making it extremely dangerous for the crew to attempt.