The Voyager 2 spacecraft hurtling toward the edge of the solar system is no longer returning useful science data, NASA announced last week, but officials are optimistic they can fix the formatting glitch believed to be causing the problem.

Artist's concept of Voyager 2 traversing the outer heliosphere. Credit: NASA/JPL-Caltech

In an interview Monday, Voyager project scientist Ed Stone said the most likely cause of the hiccup is a bit flip, where parts of a stream of data are improperly formatted.

There are "probably one or two bits which have been flipped from a 0 to 1 or 1 to 0, and that affects only the science mode data," Stone told Spaceflight Now.

Officials expect to receive more data on Thursday or Friday indicating whether the issue is a simple bit flip or a more serious software upset.

"We will be sending a command to the spacecraft to transmit down bit by bit so we can look at it and determine which bit has been flipped, and then reset it to its proper state," Stone said.

Stone said even if the anomaly is a fundamental software error, engineers can develop a software patch to uplink to Voyager 2 that should resolve the problem.

Voyager 2's distance from Earth could complicate repairs. It takes nearly 13 hours for radio signals to travel each way between ground controllers and the spacecraft.

Controllers at the Jet Propulsion Laboratory in Pasadena, Calif., uncovered the problem April 22, when science data streaming down to Earth first showed signs of an anomaly.

"The telemetry comes down in a certain format," Stone said. "For some reason, that format changed, which means that the flight data system computer was no longer formatting properly."

NASA sent commands to Voyager 2 in late April, ordering the spacecraft to switch to engineering mode. Data on the probe's health and systems is not affected by the snafu.

"All I can tell you for sure is the engineering mode and the data is coming down just fine," Stone said. "That tells us the computer is working fine and that certainly gives us some confidence."

Launched in 1977 on a tour of Jupiter, Saturn, Uranus and Neptune, Voyager 2 is about 8.6 billion miles from Earth as it traverses the outer regions of the heliosphere, or the furthest reaches of the sun's influence.

Voyager 2 and its sistership, Voyager 1, should reach interstellar space within about 10 or 20 years. Both craft have enough propellant and electrical power to operate until at least 2020, according to NASA.

Both spacecraft are now exploring a region known as the heliosheath, where the sun's solar wind is slowed by pressure from interstellar gas.