The private effort to recover the 35-year old ISEE-3 spacecraft has ended in apparent failure. In an interview on National Public Radio (NPR), Keith Cowing of the ISEE-3 Reboot Project said that though the group had been able to establish radio contact with the unmanned probe, it was unsuccessful in getting the engines to fire properly. This means it will not be able to make the planned course correction and the craft will head back into deep space.

Supported by a US$160,000 crowdfunding effort, the ISEE-3 Reboot Project was given permission by NASA to take control of the deactivated comet explorer as it passed close to Earth earlier this year. According to the Project, the team was able to establish contact with the spacecraft using the Arecibo Radio observatory in Puerto Rico in May and since then has been carrying out a series of diagnostics and spin tests.

On July 8, the Project attempted to test fire the engine needed to send ISEE-3 on its new course, and, though the first firing was a partial success, the second and third attempts failed. The team says that the most likely reason is that there wasn't enough nitrogen to pressurize the fuel tanks. They are currently crowdsourcing the problem to determine whether the nitrogen has simply run out or it has dissolved in the hydrazine used in the propulsion system.

Though the Project believes that there is a slim chance of sending the spacecraft on a different mission than originally planned, at the moment the most likely scenario is that the ISEE-3 will head back into deep space until contact is once again lost or the Project shuts the craft down again.

Sources: Space College, NPR