ISEE-3 was launched in 1978 to study the solar wind

Citizen scientists fail to revive satellite propulsion system

A team of volunteer engineers and scientist appears to have failed in their attempts to bring a 36-year-old Nasa satellite back into Earth-orbit after its propulsion system failed.

The group had won permission from Nasa to try to take control of the International Sun-Earth Explorer-3, or ISEE-3, which 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, but as the spacecraft neared Earth's orbit this spring the team launched a crowd-funding campaign to raise money, eventually ending up with nearly $160,000, and petitioned Nasa to let it try to redirect the probe into a stable orbit around Earth to 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, which was followed by more than a month of painstaking checkouts.

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 organizers 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 – a lack of nitrogen to pressurize 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 on Tuesday.

Without a course change, ISEE-3 will fly around the moon on August 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.

However, flight controllers hope to get more information about ISEE-3's condition during their next radio communications session today and 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.

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