Scientists fear NASA's comet-chasing Deep Impact spacecraft may be lost in space after a software glitch cut off communications between the aging space probe and befuddled engineers on Earth.

Artist's concept of the Deep Impact spacecraft. Credit: NASA/JPL-Caltech
 
NASA last heard from the distant spacecraft on Aug. 8, and efforts to restore contact with Deep Impact have produced no results. Engineers will continue to uplink commands to the probe in an attempt to reestablish communications, the agency said in a press release Tuesday.

Officials blame Deep Impact's problem on a software glitch, according to Michael A'Hearn, the mission's principal investigator from the University of Maryland in College Park.

"The problem was a software issue in having run the mission for many years past its design lifetime," A'Hearn told Spaceflight Now. "This basically caused an overflow in the on-board time, which in turn caused a continuous cycle of rebooting the on-board computer."

About the size of a sports utility vehicle, the Deep Impact spacecraft launched in January 2005 and reached comet Tempel 1 less than six months later, deploying a copper impactor to slam into the comet's nucleus as the Deep Impact mothership and telescopes studied material ejected from the cosmic collision.

Mission controllers reshaped Deep Impact's course several times after its primary mission ended, beginning an extended phase named EPOXI. placing the probe on course to fly by comet Hartley 2 in November 2010. Since the Hartley 2 encounter, Deep Impact used its high-resolution telescope to make long-range observations of comets Garradd (C/2009 P1) and ISON.

A'Hearn posted a status update Sept. 3 on the mission's website announcing the spacecraft's trouble, which occurred during Deep Impact's comet ISON observing campaign. Deep Impact was storing data on ISON on-board the spacecraft before beaming it back to Earth, A'Hearn said, so none of the information has been recovered.

"The challenge is to understand the present state of the spacecraft and how to communicate with it, a problem that the spacecraft team is studying very hard," A'Hearn said.

In a story posted Sept. 5 on the Nature News blog, A'Hearn said engineers are racing the clock because the probe could lose electrical power if its solar panels are pointed away from the sun.

A'Hearn told Spaceflight Now on Tuesday engineers are not sure which way Deep Impact is pointing or if it is spinning out of control.

"Since we don't have communication, we don't know whether it is tumbling or not. It is correct that we don't have control, so it might be," A'Hearn told Spaceflight Now.

Deep Impact has a steerable high-gain antenna, which requires precise pointing toward Earth to connect with controllers. Two less capable omnidirectional low-gain antennas are also aboard Deep Impact.

Built by Ball Aerospace and Technologies Corp., the Deep Impact spacecraft was intended for a brief six-month primary mission. Since its launch eight-and-a-half years ago, the probe has traveled about 4.7 billion miles, according to NASA.

Deep Impact is running low on fuel, but NASA authorized a series of rocket burns in 2011 and 2012 to alter the craft's trajectory and set up a potential flyby of asteroid 2002 GT, a mystical object that regularly crosses paths with Earth. It could be a target for future human expeditions and it has a risk of one day colliding with Earth.

If Deep Impact makes it, the flyby with 2002 GT would occur in January 2020.