Loyalty Missions (Detailed)
Loyalty missions in Mass Effect 2 become available starting in Act 2. Completing these missions for your squad members unlocks new powers for them and significantly increases their chances, and Shepard's, of surviving Act 3. While optional, these missions are crucial for strengthening your team.
Miranda's and Jacob's loyalty missions are available immediately at the start of Act 2. Subsequent loyalty missions unlock one at a time. If a character whose mission would normally unlock is not yet present (e.g., Grunt is still in his tank or Thane has not been recruited), the mission of the next available character will unlock instead. Kelly Chambers will inform you which squad members have new loyalty missions.
Each squad mate also has one Normandy Upgrade or research project. These can be unlocked in the research lab, even during Act 1, by speaking with the squad members before they offer their loyalty missions and selecting the "[NORMANDY UPGRADES]" option under the Investigate heading. Otherwise, the upgrade unlocks automatically when their loyalty mission becomes available.