The nearest exoplanet is Proxima Centauri b, about four light‑years away, so even the best gravity assists inside our Solar System can only give you a few tens of kilometres per second of extra speed. A typical plan would start with a launch from Earth, swing by Venus to reduce inclination, then another Earth flyby to boost velocity, followed by a Mars encounter for a small extra boost, and then a single big swing by Jupiter to push the craft out of the Sun’s gravity well. A Saturn assist could give a tiny additional gain, but it adds travel time and fuel for the return burn. If you want to minimize fuel while maximizing data, you’d pair the Jupiter assist with a high‑efficiency propulsion system—solar electric or nuclear thermal—so you can inject the probe into a hyperbolic escape trajectory. Even then, you’re looking at a launch velocity of about 25 km/s from Earth, giving a total interstellar escape speed of roughly 100 km/s once you’re beyond Saturn. That’s still far short of the 400 km/s or more needed for a realistic 20‑year travel time to Proxima. So the practical answer is: use a single powerful Jupiter assist, supplement it with an efficient propulsion system, and abandon the idea of using multiple gravity assists to reach an exoplanet. A high‑speed sail or a nuclear pulse engine is a more efficient path for the data‑rich, fuel‑minimal mission you’re envisioning.

That’s a solid chess‑move. The assists give you a good gravity scaffold, but the bulk of the velocity has to come from the sail or laser drive. Make sure you’ve accounted for the propellant mass of the magnetic sail—its magnetic field will need energy to stay active, and the laser drive has its own mass budget for optics and power. If you can keep the sail’s mass to a few hundred kilograms and the laser array to a kiloton scale, the 400 km/s boost is feasible, and the 20‑year window becomes realistic. Just keep the thermal loads and radiation shielding in check. Good planning, but remember the devil is in the details of the final push.