How Hall-effect thrusters stack up against other options
EP systems require significantly less propellant mass than chemical propulsion systems, and thus are favored for the cost savings and performance increases they allow. However, high specific impulse and efficiency are necessary but not sufficient conditions for an EP flight system. Throughout nearly 100 years of laboratory development each new experimental EP device has exposed a new set of challenging problems that, often, don’t fully surface until 1,000s of hours of testing or, worse, on-orbit anomalies are discovered. The promise of new propellants, plasma acceleration schemes, and power processing components have a long and frustrating history of yielding to system-level complexities such as spacecraft contamination, spacecraft charging, electromagnetic noise, or vanishing mass margins when attempting to transition into a flight product.
Your EP solution must add value to the spacecraft as a system. Benefits such as cheaper propellant, lower pressure tank, or a few percent increase in specific impulse do not outweigh the risk of catastrophic failure that can accompany The Next New Thing. The Hall-effect thruster has proven over and over that its system-level performance benefits are unrivaled. In fact, over the past 15 years Hall thrusters have “robustly outperformed chemical thrusters in terms of reliability.” Hall thrusters are trusted by the largest and most-expensive government and commercial satellites and they have never caused a mission failure. In fact, Hall thrusters have occasionally rescued multi-$100M spacecraft (AEHF-1 and GEOStar 3) when less-reliable propulsion systems failed. In the current New Space era there are a number of variant technologies seeking to challenge the Hall thruster. While maturity of these systems are low, there’s sufficient data by which they can be compared against a HET system. This table is not exhaustive, but captures a side-by-side comparison of some systems-level implications of recent electric propulsion products.