Space Probe Might Lack Nitrogen to Push It Home

A do-it-yourself team of engineers trying to lasso an aged but operational NASA space probe may have run into an insurmountable obstacle: Tanks on the spacecraft that were once full of nitrogen gas, needed to fire the thrusters, appear to be empty.

Without thrusters, there is no way to push the 36-year-old spacecraft, the International Sun-Earth Explorer-3, or ISEE-3, onto a trajectory to be captured back in Earth orbit. Instead, ISEE-3, which is otherwise in working order, will just fly by.

“Odds are, there is nothing we can do,” Keith Cowing, a leader of the effort, said Wednesday.

ISEE-3, launched in 1978, was designed to measure the wind that blows from the sun and buffets the Earth’s magnetic field. Later, it was sent to fly through the tail of a comet. After those successes, a few final firings of its thrusters in 1986 put it on course to rendezvous back with Earth in August.

In the meantime, NASA retired the probe and dismantled the transmitters needed to talk to it.

This year, Mr. Cowing, the editor in chief of the website NASA Watch, and Dennis Wingo, an engineer and entrepreneur, embarked on an effort to re-establish contact and capture ISEE-3.

Photo

An illustration of the International Sun-Earth Explorer-3. CreditMark Maxwell/ISEE-3 Reboot Project

After raising almost $160,000 on the Internet, they installed a new transmitter at the Arecibo radio telescope in Puerto Rico and set up mission control at Skycorp, Mr. Wingo’s company, in a former McDonald’s near San Jose, Calif. They successfully radioed the spacecraft in May and last week fired the thrusters to speed up its spinning motion.

On Tuesday, they attempted a longer series of firings to adjust course for a close pass of the moon on Aug. 10 that would sling it into orbit around Earth. But the thrusters sputtered.

On Wednesday, the team tried firings with different permutations of tanks, valves and thrusters. None worked, leading the engineers to suspect that the problem was not mechanical, but empty tanks. The nitrogen is used to squeeze the fuel, hydrazine, to the thrusters.

“Without that, you don’t have a rocket,” Mr. Cowing said.

There is a small chance that ISEE-3 is on course to slam into the moon on Aug. 10. A communication session on Friday will help determine its path. If it misses the moon, it will again wander in a looping orbit around the sun.

“I’m going to wave to it as it goes by,” said Robert W. Farquhar, who was the spacecraft’s project scientist when ISEE-3 launched and who came up with the idea of sending it to visit a comet.

Even though they might not be able to capture the spacecraft, Mr. Cowing said they were devising an alternative in which ISEE-3 would collect scientific data and send it back to Earth.

“There’s a Plan B,” he said. “We’re going to listen to the spacecraft as long as it talks.”

Source: The New York Times