The press kit for the first Falcon 9 Starlink launch and deployment of the first 60 satllites scheduled for May 15, 2019 says:
With a flat-panel design featuring multiple high-throughput antennas and a single solar array, each Starlink satellite weighs approximately 227kg, allowing SpaceX to maximize mass production and take full advantage of Falcon 9’s launch capabilities. To adjust position on orbit, maintain intended altitude, and deorbit, Starlink satellites feature Hall thrusters powered by krypton. (emphasis added)
Most of the electric propulsion systems that I've heard of use xenon. While the lighter krypton would have a higher Isp at a given acceleration voltage, I assume Xenon has a slightly lower ionization potential and so would be easier to ionize.
DC power for electromagnets for confinement and RF power supply for plasma excitation can dominate the weight of an ion propulsion engine (depending on the specific design and principle), so in for these svelte and featherweight spacecraft I would have thought that the'd go with the lower ionization potential of xenon which presumably can be ionized with lower electron energy.
Question: Why will SpaceX's Starlink satellites use krypton instead of xenon for electric propulsion?