As the deadline for this issue of RF Report approached, I've seen several articles saying the danger to AMC-11 from Galaxy 15 has passed, without destruction of the AMC-11 bird or interference to the cable TV channels being transmitted from the satellite. One of these is at Cable TV Interruption Avoided as Satellite Scare Passes.
There was never a risk of Galaxy 15 colliding with AMC-11, as SES World Skies maintains control of AMC-11 and could easily move it out of Galaxy 15's path, which can still be accurately predicted, if necessary. While I'm expecting most AMC-11 customers will not have interference problems, it's a bit early to be claiming that the danger has passed. SES World Skies and its consumers still have a lot of work to do.
An animated view of the positioning of the satellites around the 131 degree west longitude orbital location is available at the SES web site.
As this is being written, Galaxy 15 is just now moving close enough to AMC-11's location to cause interference, while AMC-11 is being moved east to maintain its distance from Galaxy 15. The biggest risk is yet to come. At some point, AMC-11 is going to have to stop moving east ahead of Galaxy 15 and move west beyond it to remain in its authorized orbital location. SES World Skies will relocate some customers to the newly-launched SES-1 during this move, but SES World Skies warned that customers outside the 48 continental United States may experience interference.
Monday, Web site The Space Review published an excellent article, Dealing with Galaxy 15: Zombiesats and on-orbit servicing explaining in clear terms, with graphs, the situation at 131 degrees WL and the orbital mechanics involved in Galaxy 15's drift eastern through the geostationary arc. One interesting point—the satellite could get stuck at a "libration point" at 105 degrees west longitude or, if it has enough momentum, drift through it and get captured in the 75 degree east longitude libration point over India. The Space Review thinks it likely Galaxy 15 will get trapped in the "gravitational valley" at 105 degrees WL and "oscillate back and forth either side of it, joining the 43 pieces of space debris already trapped there." The Space Review article is a must read for anyone interested in geostationary satellites. It not only describes the current situation, but gives examples of past problems and suggestions for how to manage this in the future.