Choose between passing by and staying

A flyby carries a spacecraft past a target and onward. The changing view can provide valuable observations without the resources needed to remain nearby. The best geometry may be brief, making preparation and autonomous execution important when Earth cannot supervise each action in time.

An orbiter remains gravitationally bound to the target under the mission’s operating conditions. It can revisit locations and observe changes over time, but reaching the target’s vicinity is not enough. The incoming state must be transformed into an appropriate bound trajectory, usually through a planned energy-changing process.

A propulsive capture maneuver reduces the appropriate target-relative orbital energy. Its timing, direction and achieved magnitude determine the resulting orbit. In some mission designs an atmosphere can remove energy; that introduces thermal, structural and navigation constraints rather than providing free, unconstrained braking.

Distinguish aerocapture — open definition, intended to enter a bound orbit in a single atmospheric pass, from aerobraking — open definition, which adjusts an already-bound orbit through repeated atmospheric passes. These terms describe different arrival strategies. A proposal must establish that the vehicle and target environment can support the particular method it claims.

Match the arrival to the investigation

Suppose a fictional investigation needs the same region observed across several seasons. A single fast flyby cannot directly supply that repeated time series. An orbiter may be better suited if its orbit, lifetime and instrument performance support the observations. Another question about a distant unexplored body may make a flyby the most feasible first step.

Compare mission options using both what they can measure and what they must survive. A flyby is not inherently an incomplete orbiter, and an orbiter is not automatically better for every budget or target. Each is a design with a particular evidence return, resource demand and set of limitations.