Errant Satellite To Be Back In Business Soon

Intelsat appears poised to recoup use of Galaxy 15, the wayward “Zombie Sat” that terrorized telecom satellite neighborhoods around the globe until it was brought under control late last month.

Among those breathing the biggest sigh of relief are the FAA, which is faced with the prospect of purchasing another transponder to ensure sufficient redundancy for its Wide Area Augmentation System (WAAS) out of its tight budget if the spacecraft cannot be recovered.

Intelsat reported on Jan. 13 that Galaxy 15 appears to be in good health following recovery of control in late December, after a six-month trek that took it past 15 geostationary communications spacecraft. Thanks to an often ingenious team effort orchestrated by Intelsat, other operators and customers, the incident, which occurred on April 5, did not lead to substantial interference or service loss (AW&ST Jan. 3, p. 26).

Galaxy 15 arrived at 93 deg. W. Long. on Jan. 15 for a complete checkout, including validation of three control-and-command software patches uploaded in December to ensure the incident does not recur. According to tests run so far, says Toby Nassif, Intelsat’s vice president for satellite operations and engineering, the spacecraft’s bus, subsystems, main C-band payload and WAAS L-band transponder are fully operational.

If the satellite receives a clean bill of health, Nassif says, it could be available for in-orbit backup services as early as Jan. 31 as it is begins its drift eastward either to 129 or 133 deg. W. Long., its original position. Launched in 2005, Galaxy has more than 10 years of revenue potential left, and its return to service would obviate the need for acquiring a replacement, though much of its book value has been written down.

Leo Eldredge, the FAA’s satellite navigation system manager, says the transponder beacon, which remained operational until increasing signal unreliability forced it to be shut down on Dec. 16, began broadcasting again on Jan. 6 in test mode. Engineers were able to bring on-line a new transponder on Inmarsat 4/F3 before shutting down the Galaxy 15 beacon, averting loss of service. Introduction of the Inmarsat payload, initially due in late December or January, had been accelerated to permit the switchover.

In fact, Eldredge says, although temporary service interruptions had been feared during the Zombie Sat saga, none were in fact observed. A second transponder on Telesat’s Anik F1R ensured full redundancy and extended coverage throughout the WAAS service area except for 16 airports in northwestern Alaska, which lost the use of localizer performance with vertical guidance (LPV) capability, a high-precision WAAS-enabled instrument approach. However, the loss was moot because the airports had not yet published LPV procedures. And they retained the ability to utilize non-precision lateral navigation (LNAV) approaches, which do not require WAAS, as long as aircraft verified the availability of RAIM (receiver autonomous integrity monitoring) before flight.

If Galaxy 15 is recovered, Eldredge says, the FAA will be able to curtail a new procurement, dubbed Stop Gap GEO, it had initiated after the satellite lost control. Because of the 3-4-year lead time needed to purchase a new transponder, the FAA typically maintains a fleet of three transponders for WAAS service.

Use of the service is increasingly important as the fleet of aircraft equipped to use it gradually ramps up. According to Eldredge, the FAA has more than 2,341 published LPV procedures—twice the number of legacy instrument landing systems—and more than 50,000 aircraft carry WAAS receivers. Most users are in the general aviation category, but helicopters are increasingly adopting WAAS and more than 50 air transport types have been approved, or are near approval, making it likely service will grow over the next few years.

Meanwhile, Intelsat says engineers are focusing on firmware in the baseband equipment (BBE) command unit as the source of the Galaxy 15 incident, and they hope further testing will enable them to narrow down and complete the failure review board inquiry initiated under the control of Orbital Sciences Corp., which built the spacecraft. OSC has also uploaded the software patches, which were validated in orbit in October, on other Intelsat spacecraft that use the same Star 2 bus employed in Galaxy 15.

Enhancements include a modified emergency command channel, using a fully independent communications path, that permits the spacecraft to be commanded and operated if the BBE command malfunctions, a patch that turns off the payload automatically if no commands are received for 21 days, and a patch to reset the BBE if no commands are received for 14 days.

Of the 120 potential root causes identified, only two remain. Solar flares, the long-rumored culprit, are not one of them. OSC plans to issue a final failure review report in February.