“Krypton propelled spacecraft”?
Ion propulsion. Typical plasma gas for "propulsion" is xenon. Krypton is also a nobel/inert element, not as heavy as xenon, but more plentiful.
Many satellites launched into (same) orbit. The satellites then need to spread out to make a constellation more useful from earth. In the long run, the satellits need to maintain some sort of orbit pattern, so "propulsion" (low force) is necessary in an ongoing fashion.
“Krypton propelled spacecraft”?
Ion thrusters.