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In order to become a TSC member, someone on the TSC must nominate the Contributor. The individual may then be approved with a 3/4 majority of the PMC TSC (project membership community?). As with becoming a Committer – a nominated person is expected to have already demonstrated shouldering a major set of the above responsibilities. .
Emeritus TSC members
The amount of time one can dedicate to an open source project tends to ebb and flow. While this is totally OK for almost any role, participation in the TSC requires at least an amount of time appropriate for intelligently casting votes. If that becomes a problem and existing TSC member may decide to transition to the Emeritus status. At that point the person is no longer considered a TSC member for the purposes of quorum or majority votes, but can transition back to a full TSC member status by simply emailing the TSC mailing list and asking for it.