It appears to be somewhat random in its availability, but the frequency depends on how good your team is. However, if you become the number 1 driver for your team where you can control the level of R&D taken on by your team, and setting it higher will bring about more opportunities.
The race engineer will likely not give you a new objective every race, at least initially, as you start with the lesser teams and an intermediate path setting by default. This can change however, when the players team promotes you into the number one drivers slot, giving you the choice to further your research & development or curtail it in favor of improving next years package
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