Artist’s illustration of the ISEE-3 spacecraft. (Image Credit: NASA)
In 1978, NASA’s International Sun Earth Explorer 3 (ISEE-3) was launched to investigate solar wind and how it interacted with the magnetic environment. Eventually, NASA redirected the mission, which was renamed the International Cometary Explorer (ICE), toward the Giacobini-Zinner comet. The spacecraft flew through the comet’s tail in September 1985, and NASA ended the mission support and operations in 1997. It left the spacecraft in solar orbit.
In 2014, ISEE-3 returned to Earth’s vicinity for the first time in decades. A crowdfunded team of engineers, radio specialists, and programmers worked with SkyCorp to take control of the spacecraft to redirect it. Before doing so, the initiative got NASA’s permission to rebuild its communication capability, using software-defined radio technology and radio telescopes.
Two-way communication was re-established in May 2014. From there, it transmitted commands, and the probe sent telemetry data back. With this capability restored, the team examined the probe’s condition and attempted to redirect it to a practical Earth-Sun orbit. For the first time since 1987, they commanded eleven short thruster pulses on July 2nd, boosting the revolutions per minute from 19.16 to 19.75.
Although the team restored its original spin, a trajectory-altering maneuver failed on July 8th. The citizen scientists needed to change the velocity by 7.3 meters per second for a trajectory adjustment to achieve a planned lunar flyby. Their goal was to send ISEE-3 toward the Sun-Earth L1 region. However, that burn generated 0.15 meters/second before the thrust rapidly declined.
According to telemetry data, an empty fuel tank probably didn’t cause the problem. The probe’s propulsion system used hydrazine as propellant. Pressurized nitrogen forced the liquid hydrazine through fuel lines toward its thrusters. A catalyst then decomposed the hydrazine into hot gases that created thrust. Telemetry indicated that the nitrogen pressurant was depleted. Nitrogen leaking while the ISEE-3 probe drifted in space means the system wouldn’t deliver a sustained supply of propellant. This may explain why the spacecraft was able to short-fire, while the longer maneuver failed. However, since the team couldn’t physically inspect the spacecraft for issues like a leak, the diagnosis remains unconfirmed.
Because the velocity didn’t change, the ISEE-3 spacecraft flew 15,600 km from the Moon on August 10, 2014. It could not enter the planned return trajectory and remained in heliocentric orbit. The team still managed to power on scientific instruments and collect scientific data. They lost contact with the spacecraft on September 16, 2014 as if moved away from Earth.
Instead of abandoning the mission, the team received telemetry from the activated instruments. They made the resulting observations available online. In August 2014, the Planetary Society announced it had created a public home for the ISEE-3 data. Researchers and the public can access measurements of the spacecraft.
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