SpaceX filed with the FCC to modify its Ku/Ka-band NGSO license to relocate satellites previously authorized to operate at a lower altitude of 550 km and to make other changes. Here is a link to SpaceX's 83 page technical report with its filing. The first generation of SpaceX Starlink satellites will have a simplified design for faster development and deployment. There will be continuous improvement and addition of features in subsequent generations. Initial deployment of 1,584 satellites operating at 550 km with 25 degrees minimum earth station elevation angle. Insertion altitude for the modified satellites will be 300-350 km (depending on solar activity). This will require less fuel for orbit raising. Atmospheric drag at 550 km is significantly higher but the new design reduces Hall-effect electric propulsion work by 50%. Operating at lower altitude increases reliability by reducing radiation intensity and reduces collision chance in congested 550 – 1,150 km LEO orbits. Satellites will re-enter atmosphere ≈6 months after end of mission. 550 kilometer altitude is a self-cleaning orbit. Debris lifetime is days or weeks. The longest decay time of failed spacecraft is about 5 years.