Posted on behalf of Mark Zastrow.
An ambitious citizen-science effort to revive and redirect a decades-old NASA spacecraft has hit a snag. The International Sun-Earth Explorer-3 (ISEE-3) probe, now roughly 5 million kilometres from Earth, appears to be out of the nitrogen gas that it needs to pressurize its propulsion system’s rocket thrusters.
This means that the volunteer ISEE-3 Reboot Project will not be able to manoeuvre the 35-year-old craft and place it in a holding orbit at the L1 point between the Earth and the Sun, where the two bodies’ gravitational pulls cancel out. Instead, ISEE-3 will fly past the Moon on 10 August and reenter an orbit around the Sun. However, the team is still in communication with the probe and intends to collect scientific and engineering data as long as it holds out — perhaps for years to come.
The group, led by former NASA employee and journalist Keith Cowing and entrepreneur and engineer Dennis Wingo, hoped to use ISEE-3 to monitor space weather or even fly by a comet. A crowdfunding campaign raised nearly US$160,000 for the effort, which allowed the group to purchase control of the satellite from NASA — the first time that the agency has contracted out a defunct spacecraft. The team successfully reestablished contact with ISEE-3 in May and fired its thrusters to adjust its spin rate last week. They were attempting a series of fuel burns to alter its course early Wednesday morning (GMT) when its rockets hiccupped and ran out of nitrogen.
The ISEE-3 Reboot Project has pushed back against notions that the reboot mission is over, saying Thursday on Twitter that “ISEE-3 is going to be useful for YEARS” even in its uncontrolled orbit.
Robert Farquhar, ISEE-3’s NASA flight director when it launched in 1978, was more downbeat on the craft’s scientific prospects. “I don’t believe that,” he says. “It’s going be too far from the earth. It’s not going to be that useful.”
But Cowing says the team is in the process of forming an ad hoc network of radio dishes that can maintain contact with the satellite even in deep space. He also says that the fact that the craft and 9 of its 13 instruments are still working after 35 years in space is valuable engineering data in itself. Michael Combi, a space physicist at the University of Michigan agrees and says that it can stand as a comparison to the Voyager probes, which launched one year before ISEE-3.
In the meantime, the loss of nitrogen in ISEE-3’s thrusters has left the team puzzled. “I’ve never heard of a spacecraft losing all of its pressurant like that,” says Farquhar, who has advised the citizen-science group. One early suspicion is that the nitrogen may have dissolved into the hydrazine fuel it was intended to pressurize. Farquhar, who put the ISEE-3 reboot’s odds of success at 50-50 back in March, still says Cowing and Wingo’s team has done “a tremendous job.”
The citizen-science mission was intended to be a homecoming of sorts for ISEE-3. Originally launched to study the magnetic interactions between the Earth and the Sun, the probe was diverted through the tail of Comet Giacobini-Zinner in 1985, making ISEE-3 the first spacecraft to explore a comet. NASA intentionally put it on a meandering course to fly by Earth this year, nearly 20 years later, allowing for the possibility of retrieval.