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Intelsat Galaxy 15 drifts from Zombie to a Phoenix-like Recovery

Satellite Technology

Satellite Technology Feature Article

January 13, 2011

Intelsat Galaxy 15 drifts from Zombie to a Phoenix-like Recovery

By Doug Mohney, Contributing Editor


Intelsat held a press conference via webcast today to recap what it called an "Unprecedented event" around its Galaxy 15 satellite trouble along with "unprecedented cooperation" among satellite operators to make sure the satellite's wayward drift across geostationary slots over North America didn't affect anyone. It also revealed what it believed to be the root cause of Galaxy's trouble and the steps it has taken to mitigate potential problems in other satellites of the same type.


On April 5, Galaxy 15 suffered an "anomaly" in its telemetry and control system, making it no longer able to respond to commands, transmit on-board telemetry, or perform station-keeping maneuvers. However, in one of those good news/bad-news cases, the satellite otherwise operated normally, with its C-band and WAAS L-band payloads operating "nominally," and all other housekeeping functions to keep the satellite running working A-OK.

Orbital Sciences Corporation, manufacturer of Galaxy 15 and its STAR (News - Alert)-2 satellite bus, launched an investigation and narrowed down to a mixed set of 3 hardware failures and two software failures.  Until the satellite "off-pointed"/lost lock on Earth, forcing a shutdown of the payload and a systems re-boot, there was little Intelsat (News - Alert) could do in direct recovery efforts, other than prepare plans to recover the satellite if it wasn't a fatal hardware issue.

Meanwhile, Galaxy 15 slowly drifted out of its orbital slot at 133 degrees West and proceeded eastward, merrily continuing to broadcast in C and L-bands -- and across the orbital slots of 15 other satellites -- before it finally reached off-point and went into shutdown mode on December 17; Intelsat had initially predicted that off-point would occur in September.  Thus ended the phase with which the press (myself included) called Galaxy 15 "ZombieSat."

During the April-December tour across geosync orbit, Intelsat had to work with other satellite operators in order to mitigate the effects of Galaxy 15's unplanned broadcast fly-by. Intelsat says service impact across all other satellite operators was "minimal," and didn't cost anyone a lot of money, but I'd be surprised if there weren't some quiet quid pro quos down the road.

Perhaps it should be no big surprise that Intelsat dubbed the week of December 17-23 as its "Spacecraft Phoenix" event, as engineers re-established communications with the satellite and climaxing in stabilization of the craft, putting it into safe mode, and uploading three software patches to prevent Galaxy 15 from repeating its previous behavior.

Technical investigation by Orbital Sciences (News - Alert) Corporation revealed that an ESD (electrostatic discharge) event had locked up the FGPA within the Star-2 bus BBE (broadband equipment). The failure was reproduced on the ground by Orbital and revealed a "sweet spot" vulnerability within the BBE. With lower levels of BBE, the equipment just ignores the ESD and keeps operating. At higher levels, the primary BBE shuts down and the backup BBE takes over.   Hit the sweet spot, and you get a satellite that can't accept commands from the ground.

Intelsat emphasized that the failure was due to ESD -- not solar activity around April 7.   Company officials seemed impassioned that bad reporting had taken place when Galaxy 15 encountered troubles, with many in the media jumping to the conclusion that sunspot activity had caused the satellite to lose touch with the ground.

More significantly, Intelsat has uploaded three software patches to all of the Star-2 based satellites in its fleet to prevent a potential repeat of Galaxy 15's wayward journey. An Emergency Command Channel (ECC) patch provides an independent communications path outside of the BBE.   A payload turn-off patch turns off the transmitters if no ground commands have been received in 21 days. Finally, a BBE reset patch resets the BBE if no commands have been received in 14 days.

Galaxy 15 is now undergoing an extensive testing and checkout of all subsystems as it drifts to an orbital slot at 93 degrees west. Intelsat could have the checkout done as early as the end of this month and then it must decide if it will move the satellite to an orbital slot at 133 or 129 degrees West. But the company believes the satellite will remain in operation up until its expected lifetime of 2022.


Doug Mohney is a contributing editor for TMCnet and a 20-year veteran of the ICT space. To read more of his articles, please visit columnist page.

Edited by Stefanie Mosca

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