In 1999, as the world was bracing for Y2K, NASA trashed some old transmitters it had used to talk to spaceships that were no longer in use.
But one of those spaceships forgot to die.
ISEE-3 was launched in 1978, conducting groundbreaking missions that included studies of solar wind and comet flybys. In 1997, it was left to sail away, 850 pounds of metal floating through the junkyard of space. But someone neglected to turn it off.
In 2008, NASA realized the poor satellite was circling the sun, still waiting for orders from its home planet. But those orders never came. Even though scientists could listen to ISEE-3"”determining 12 of its 13 instruments were still working"”they had no way of telling it what to do next. It spoke a lost language.
Next month, ISEE-3 will finally come home, its first visit in 30 years (its slightly faster orbit means it has done 31 laps of the Sun in the same time Earth has done 30). It would have been the perfect chance to use the Earth's gravity to send it on a new mission. Everyone thought it was a lost opportunity. ISEE-3 would miss Earth and sail right on by, floating farther and farther out of our reach.
Enter Skycorp. The California company asked NASA to let it try to save ISEE-3. The agency had said earlier that trying to rebuild the necessary transmitters wasn't worth the investment. With nothing to lose, NASA gave Skycorp permission to try to talk to its forsaken satellite.
If all goes according to plan, ISEE-3 will steer with its thrusters Tuesday for the first time since Ronald Reagan was in office. Skycorp hopes to steer it into Earth's orbit and again use it to take scientific measurements. It plans to live-share the data it collects with the public. Here's how their plan has worked so far.
1. Get some money. Before Skycorp could make a bid to save the spaceship, it needed funding. Thanks to satellite enthusiasts on the Internet, it was able to raise well in excess of its $125,000 goal.
2. Find a partner. To communicate with ISEE-3, Skycorp needed transmitters that no longer exist. Rather than digging out old manuals and rebuilding the transmitters, the company approached Ettus Research. Ettus uses what's known as software-defined radio, which uses processors to replicate the functions of many different types of hardware. Ettus software "emulates all of the hardware equipment NASA used to have," said Skycorp CEO Dennis Wingo.
3. Get permission. On May 21, NASA gave the go-ahead for Skycorp to try to save its satellite. The agency agreed to share technical data with Skycorp, citing the company's pledge to share its findings with the scientific community.
4. Establish contact. Just a week after NASA handed over the keys to ISEE-3, Skycorp made contact with the satellite and began giving it commands"”the first such communication in 16 years.
5. Find your satellite. Though the general orbit of ISEE-3 was well-known, scientists were dealing with a 20,000 mile window"”some parts of that range would have the satellite on course to crash into the moon. Skycorp's first instructions to ISEE-3 were to turn on its telemetry.
6. Give it directions. On July 2, Skycorp fired thrusters to speed up the satellite's rate of spin. The course corrections will put ISEE-3 in a better position to communicate with Earth.
7. Check your instruments. Once ISEE-3 is in a better communication spot, Skycorp will run tests on its 13 instruments. For now, it's at least getting data from some of them. The company reported on July 1 that the magnetometer had detected a recent solar event.
8. Fly home. The real test will come Tuesday, when engineers try to change the satellite's trajectory and push it back into Earth orbit. Dr. Robert Farquhar, who coordinated the ship's comet missions, is overseeing the direction shift. Only a few days remain to try, given the ISEE-3's orbit and thrust capacity. And no one knows if the ship has leaked fuel or the engines still function correctly. But if everything works, Skycorp will have successfully saved a satellite from decades of aimless solar wandering.