Out of options to rescue satellite

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iol scitech july 11 ISEE-3 AFP This artist's concept obtained from Nasa shows the International Sun-Earth Explorer, or ISEE-3, built in 1978 to study the physics of solar winds.

Cape Canaveral - A valiant effort to put a defunct Nasa science satellite back to work came to a disappointing end this week after the 36-year-old spacecraft's propulsion system failed, project organisers said.

An ad hoc team of engineers and scientists won permission from Nasa to try to take control of the International Sun-Earth Explorer-3, or ISEE-3. The spacecraft was launched in 1978 to study the solar wind, a continuous stream of charged particles flowing from the sun.

A second mission to study comets followed in 1981, after which the satellite entered a graveyard orbit around the sun.

As ISEE-3 neared Earth's orbit this spring, a volunteer team launched a crowd-funding campaign to raise money, eventually ending up with nearly $160 000. The group also petitioned Nasa to let it try to redirect the probe into a stable orbit around Earth so it could resume science operations.

The Arecibo Observatory in Puerto Rico offered free telescope time and the group made two-way radio contact with ISEE-3 on May 29. More than a month of painstaking checkouts followed. Last week, flight controllers finally coaxed a tiny thruster burn out of ISEE-3, which made it spin slightly faster, steadying it for the long series of engine firings needed to change its orbit.

The trajectory shift began on Tuesday but the joy was short-lived.

“We didn't see the accelerometer moving,” Keith Cowing, one of the organisers of the ISEE-3 Reboot project, told Reuters.

Initially, the team thought the spacecraft had a stuck valve, but additional troubleshooting on Tuesday and Wednesday pointed to a more serious problem: no more nitrogen to pressurise the fuel system.

“We think there is a chance that the nitrogen may have been depleted,” the team wrote in a status report on the project's website.

Without a course change, ISEE-3 will fly around the moon on Aug. 10 and resume its trek around the sun. The thruster burns were intended to put ISEE-3 in a gravitationally stable orbit about 932 000 miles (1.5 million km) from Earth, from where it could resume its original mission to observe the solar wind hit the planet's magnetic field.

Flight controllers hope to get more information about ISEE-3's condition during their next radio communications session on Friday.

Even if the optimal orbit is no longer possible, the team hopes to use ISEE-3 for science while it is still within the inner solar system, Cowing said. - Reuters

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