April 8, Intelsat disclosed that its Galaxy 15 telecommunications satellite had abruptly stopped responding to commands from the ground. Premature satellite failures are never a good thing, but Intelsat noted that Galaxy 15’s C-band transponders remained fully functional, giving the company time to reposition another spacecraft to avoid a disruption of service.
But the resilience of Galaxy 15’s payload proved to be a short-lived blessing. The satellite began to drift — as do all geostationary-orbiting satellites once they lose their station-keeping abilities — and with its transponders ready to receive, amplify and rebroadcast any signals encountered in the right frequency range, Galaxy 15 would soon pose a serious interference threat to other C-band satellites in its path.
As it turned out, the first satellite in harm’s way was AMC-11, operated by Intelsat’s primary global competitor, SES. It was an unprecedented situation that required unprecedented technical cooperation between the rivals to avoid an outage of AMC-11 service, which would have affected cable television and other media customers operating in the United States.
Responsibility for troubleshooting the problem fell largely on Alan Young and Thierry Guillemin, the chief technology officers at SES World Skies and Intelsat, respectively. Working together, Young, Guillemin and their teams devised an interference-mitigation plan that entailed, among other things, rerouting AMC-11 signal traffic through an Intelsat teleport antenna in Clarksburg, Md. Meanwhile, as Galaxy 15 approached from the west, AMC-11 was moved eastward to the far end of its orbital location, or neighborhood, to keep its distance from the stricken craft. Then, as Galaxy 15 drifted deeper into AMC-11’s neighborhood, the SES satellite was quickly moved in the opposite direction, past the Intelsat craft and into its original position.
Young likened the scenario that played out to a gaming exercise for aerospace engineering students, only this was the real thing. In the end, the orbital high-wire act worked, averting a costly outage with a potentially messy aftermath. In devising and then executing their plan to perfection, Young and Guillemin helped set a standard for cooperation among satellite operators who likely will face similar scenarios as Earth orbit becomes more crowded.
