Mission planners keep asking whether a spacecraft can move. The harder question is how much useful maneuvering capability survives a full mission of contingencies, degradation, and end of life constraints.
For decades, mission planners asked the easy question: can the spacecraft move? The answer was usually yes, the propulsion stack lit on time, and the mission proceeded. The harder question is the one that should have been on the table from the start: how much useful maneuvering capability will still be available when the original plan has been bent by a year of orbit corrections, a missed rendezvous window, a debris-avoidance burn, and a thruster that came back from rest a little cooler than its qualification limit?
That is the question a recent piece of trade-press commentary has been pressing, and it is overdue. As the mission set shifts from placement and station-keeping to repeated, sustained maneuvering (reposition, retask, inspect, avoid threats, persist, support logistics, preserve optionality), the launch-day capability answer is no longer enough (SpaceNews analysis of the gap). What mission owners need is a number for maneuver margin: the useful propulsion reserve that survives planned operations, contingencies, degradation, qualification margins, restart uncertainty, and end-of-life constraints.
The blind spot is procurement, not propulsion. Most propulsion on current missions is still specified generically, against launch-day capability, rather than against a defined mission envelope. The result is a vehicle that can technically execute a maneuver and a program office that has no defensible answer to the question of how many maneuvers are left in the tank when the unexpected arrives. That is a procurement failure mode, not a technical preference.
There are real examples of the reframe working. NASA's Double Asteroid Redirection Test used a gridded ion thruster developed at NASA Glenn Research Center to execute a sustained, planetary-defense-style maneuver, treating the propulsion budget as a resource to be spent across the mission rather than a one-burn deliverable (SpaceNews). It is one mission, and the source is right not to over-generalize from it, but it illustrates the working definition: a published mission that planned its propulsion around the envelope, not just the launch-day check.
The practical takeaway for mission owners, program offices, primes, and propulsion teams is straightforward. Define the mission envelope before locking in the propulsion answer. Enumerate the planned burns, the contingency burns, the restart scenarios, the degradation curve, the qualification margins, and the end-of-life constraints. Only then does a specific impulse, a thrust level, a fuel margin, or a thruster class become a meaningful number.
Until that becomes the default conversation, the industry will keep buying launch-day propulsion for missions that are really asking for mission-life maneuver margin.