WASHINGTON — NASA’s International Earth/Sun Explorer (ISEE)-3 will not be resuming its original mission after all, now that citizen scientists and engineers striving to rescue it discovered July 9 that the old heliophysics observatory’s propulsion system is not working.

“There was no burn and we detected no acceleration and nothing was coming out of the engines,” NASAWatch.com Editor Keith Cowing, who spearheaded the ISEE-3 Reboot Project along with entrepreneur Dennis Wingo, said in a July 9 phone interview.

“We really can’t do anything,” Cowing said.

The widely read blogger spoke to SpaceNews after a failed attempt to complete the remaining engine burns that project officials thought would be required to send the spacecraft, currently in a heliocentric orbit, back toward the gravitationally stable Earth-sun Lagrange Point 1. From that position, the 1970s-vintage spacecraft was expected to be able to resume observations of solar winds breaking against Earth’s magnetosphere.

“We’ve done our best, but we’re now looking at a flyby,” Cowing said. Controllers at the ISEE-3 Reboot Project’s main ground system at the Arecibo radio observatory in Puerto Rico have switched the craft over into science mode, which will allow its instrument to collect and beam data back to Earth for as long as anyone is willing to listen for it.

Practically speaking, that will be about three more months, Cowing said. After that, the spacecraft will have traveled so far away from Earth that communicating with it will require receiving stations so large that the expense would simply not be worth it.

Before the July 9 attempt, the ISEE-3 Reboot Project thought it had a chance of completing its planned trajectory correction maneuver. The spacecraft’s small hydrazine thrusters were spun up July 3, and systems appeared nominal, Cowing said. On July 8, the spacecraft even managed to perform one of the six multipulse burns that would have set it up for a return to the orbit into which it was launched in 1978.

But further attempts to activate the thrusters July 8 proved unsuccessful, as were all attempts the following day. After eliminating a malfunctioning valve as the cause of the problem, the ISEE-3 Reboot Project was forced to conclude that the satellite’s hydrazine fuel simply was not being pushed through its plumbing at the right pressure to conduct a burn.

The thruster firings that occurred July 3 and 8 were “probably the result of residual hydrazine that was already in the system that had pressure,” Cowing said. “We were a little misled that we got this perfect burn.”

The ISEE-3 Reboot Project efforts were funded with $160,000 raised on the crowd-funding website RocketHub.com. Another fundraising drive likely would have been required for the citizen science campaign Cowing and Wingo were planning.

“We did stuff that was widely seen as impossible, improbable, and impractical,” Cowing said. “You need to focus on the absurd things that are possible.”

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