Satellite Rows could be uniquely identified by a combination of the Governing (Hub or Link) Key and The Row Start Date.
Depending on the Technology being used to implement the Vault, it is often efficient to provide an incrementing unique key on the tables.
This means that you have a unitary key for referencing each row, without relying on a Date / Time column.
An example of where this is useful is when building PIT (Point In Time Tables), where you hold the key for each Satellite, at a point in time, to assist in query performance.
A Unitary Key is far more elegant that a combination of a Surrogate and a Date.