Zombie Satellite Galaxy 15 Still Won't Die
The Galaxy 15 satellite is seen before its 2005 launch to geostationary orbit nearly 36,000 kilometers over the Earth's equator.
Credit: Orbital Sciences.

A wayward satellite that has spent months drifting in orbit has not shut itself down as originally predicted, and continues to pose a signal interference risk for other craft.

The so-called "zombie satellite," Intelsat's Galaxy 15 communications satellite, lost contact with ground controllers in April, but continues to follow a stable path as its operators on Earth work to avoid potential interference with other nearby spacecraft.

In an unprecedented satellite malfunction, the telecommunications broadcast package on Galaxy 15 is stuck on and still transmits signals, but ground controllers are unable to control the solar-powered craft. Intelsat engineers initially estimated that the satellite would lose power and shut itself off in late August, but so far, that has not happened.

"It has not powered down yet, and it continues to drift ? but, we still know where it's going, and it's still following a predictable path," Intelsat spokesman Nick Mitsis told SPACE.com.

The team's main focus is preventing Galaxy 15's signals from interfering with neighboring satellites, since Intelsat officials have said there is no risk of it physically colliding with other spacecraft.? [Worst Space Debris Moments in History]

How it all started

The 4,171-pound (1,892-kg) satellite went rogue on April 5, when it stopped responding to controllers on the ground. Intelsat has been investigating the cause of the glitch, including the possibility of a solar storm interference.

Following the anomaly, the spacecraft started veering off its assigned orbital slot of 133 degrees west longitude, 22,000 miles (36,000 km) over the equator, yet the "zombie satellite" maintained an active payload, with its C-band telecommunications transmitter still functioning.

At the moment, Galaxy 15 is drifting close to the orbit of Mexico's Satmex 5 communications satellite, and will make its closest approach on Sept. 21.

"We're working with Satmex and sharing the Galaxy 15 information that we have right now," Mitsis said. "We're relaying lessons learned from previous flyby sessions and offering recommendations for Satmex to support their maneuver."

Most recently, Intelsat engineers assisted Telesat, a satellite services provider headquartered in Ottawa, Canada, as Galaxy 15 swooped by the Canadian Anik F3 satellite. The flyby was completed safely without any signal interruption on Sept. 14.

Before that, Intelsat oversaw four other flybys of satellites in its own fleet, including Galaxy 13 and 14.

In May, the satellite operator SES World Skies ? whose AMC-11 satellite passed nearGalaxy 15's path at the time ? worked with Intelsat to successfully perform a series of intricate maneuvers to avoid interference and service interruptions.

What comes next

Several attempts to shut down Galaxy 15 have been unsuccessful, leaving the defunct satellite stuck drifting in the cosmos.

Ultimately, the satellite is expected to lose its Earth-pointing capability. Once this lock on Earth is lost and its solar panels will no longer be pointed at the sun, the satellite's battery power will eventually die.

"Without power, the satellite would not be able to cause any interference," Mitsis said. "It will power down, shut off, and if it doesn't reboot, then it will become space debris."

There are about 500,000 known pieces of orbiting space junk. Of those, about 21,000 objects are larger than 4 inches (10.1 cm) in diameter, and are being tracked by the Department of Defense's U.S. Space Surveillance Network. These are items like spent rocket stages and broken satellites such as Galaxy 15.

Space debris ? even tiny pieces of it ? can be dangerous because they orbit the Earth at high speeds and pose risks for impacts and collisions.

Galaxy 15 launched on Oct. 13, 2005 on a European Ariane rocket. The spacecraft's manufacturer, Orbital Sciences Corp. of Virginia, has said that an intense solar storm in early April may have caused the breakdown in communication.

Meanwhile, Intelsat continues its own technical investigation, but has yet to reach any definitive conclusions on the cause of the glitch.

"This continues to be an unprecedented event for the entire industry," Mitsis said. "The good news is, we haven't had channel losses, we haven't had programming losses, and we're very thankful for the cooperation we're getting from our satellite neighbors."