LOS ANGELES – Mission controllers ordered NASA's Deep Space 1 to turn off its pioneering ion engine and then cut its radio umbilical cord to Earth on Tuesday, sending the spacecraft on its way around the solar system on its own.
Deep Space 1 tested a dozen cutting-edge spacecraft technologies and then flew by an asteroid and a comet before the 3-year-old mission was brought to an end by a command sent from NASA's Jet Propulsion Laboratory in Pasadena at 12:45 p.m. PST.
At nine seconds past 1 p.m. the spacecraft's transmitter fell silent. For a while a big Deep Space Network antenna at Canberra, Australia, searched for the signal to make sure the silence wasn't just an accident of the 86.5 million-mile distance.
"It makes one feel wistful, but it went very smoothly," said project manager Marc Rayman, who worked on the mission since its inception in mid-1995.
Deep Space 1's core systems were left on to allow it to point its solar arrays at the sun to keep its batteries charged, control its temperature, monitor its own systems and to take corrective actions if necessary.
Its radio receiver also was left on.
"In case we change our mind," Rayman said. "You know, you never know when tomorrow somebody's going to say, 'Oh wait, I just thought of one more good thing.'"
Controllers had to defeat protective software that endlessly analyzes onboard systems and wants to call home if trouble surfaces. A timer that turns on the transmitter if it hasn't heard from Earth in two weeks was reset to more than 50 years.
The craft will die in three to 12 months when it runs out of the hydrazine fuel used by thrusters to keep it properly pointed, Rayman said.
After that it will keep circling the sun unless by some unlikely chance it collides with an asteroid or, in thousands or millions of years, has its orbit changed by gravitational influences and is perhaps ejected from the solar system or hits a planet.
The mission will have cost just over $159 million when funding for science work runs out at the end of next year.
Among its technical achievements were tests of an autonomous navigation system, but Rayman said he considers the demonstration of ion propulsion, once the stuff of science fiction, to be the mission's greatest success.
"It will allow us to go places and do things that have, prior to Deep Space 1, been completely beyond our reach," Rayman said.
The engine had to run 200 hours for the minimum success; when it was turned off it had run for a total of 677 days.
"It was operating happily right up to the end and has been a dream to control," Rayman said.
Deep Space 1's primary mission came to an end with a flyby of the asteroid Braille. Then, as the mission was being extended in late 1999 for a flyby of the comet Borrelly, the craft's vital star tracker failed.
"I think most of us were pretty down," Rayman said. "It wasn't the way we wanted to end it."
Mission engineers managed to reconfigure Deep Space 1 to overcome the problem and in September 2001 it passed Borrelly at a distance of 1,349 miles and sent to Earth the highest-resolution pictures ever taken of a comet.