Only a few days after one of its successors approached a comet in deep space, the International Sun-Earth Explorer (ISEE-3) spacecraft made its closest approach to Earth, shortly followed by a lunar flyby this past weekend. ISEE-3 recently made the news because it was successfully “rebooted,” after being defunct for 17 years, by a group of citizen scientists. This milestone came days before the spacecraft celebrated its launch “birthday.”
On Saturday, Aug. 9, ISEE-3 made its closest approach to Earth. On the following day, the spacecraft came within 9,700 miles (15,600 kilometers) of the Moon. This flyby comes after unsuccessful attempts to fire the spacecraft’s thrusters in July; it is believed vital nitrogen gas has been depleted in the spacecraft’s propulsion system (this gas pressurized the system). The ISEE-3 Reboot Project citizen scientists intended to restore the vintage spacecraft to a “halo orbit” at the Sun-Earth Lagrangian Point; ISEE-3 was the first spacecraft to enter such an orbit after its initial commissioning.
While a return to its desired orbit was not reached, the scientists still intend to pull data from ISEE-3, as long as it continues to communicate with Earth. The team announced the “ISEE-3 Interplanetary Science Mission” on July 24; thus far the spacecraft has detected solar data. Five of its 13 experiments are still functioning—no mean feat after nearly four decades in space.
Earlier this year, an initiative was announced to fund a “reboot” of the long-dormant spacecraft (it had been decommissioned in 1997). Through a crowd-sourcing effort, needed funds were raised to reestablish communication with ISEE-3; funding through NASA was not possible, as the spacecraft was considered a low priority for the agency. In May, AmericaSpace reported: “In an unprecedented move, NASA signed a Non-Reimbursable Space Act Agreement with Skycorp, Inc., a company based in Los Gatos, Calif., which would allow them to ‘possibly command and control’ the spacecraft, according to NASA. This is the first time the agency has signed such an agreement concerning a decommissioned spacecraft.”
This weekend’s milestone came days after one of ISEE-3’s successors, Rosetta, approached comet 67P/Churyumov–Gerasimenko in a first-of-its-kind rendezvous. ISEE-3 has its own unique history in the field of cometary science. According to the previous AmericaSpace article cited, the spacecraft was an early intrepid comet chaser: “In 1982, ISEE-3 began its secondary science mission and was rechristened the International Cometary Explorer (ICE). In 1985, it became the first spacecraft to encounter a comet, when it passed through the tail of Comet Giacobini-Zinner; in 1986, it went on to transit between the Sun and Comet Halley.”
In fact, the spacecraft’s visibility studying Halley’s Comet in 1986 was memorialized in an educational video released last week by the European Space Agency (ESA) prior to Rosetta’s rendezvous. While the “Halley Armada” included the ESA’s Giotto, the Soviet Union’s Vegas 1 and 2, and Japan’s Suisei and Sakigake, ISEE-3 (by then ICE) also received data in its transit between the comet and the Sun.
In addition, days after scientists and engineers waved “goodbye” to ISEE-3 as it made its closest approach to Earth, the spacecraft celebrated its 36th birthday. ISEE-3 was launched on Aug. 12, 1978, by a Delta 2914 rocket from Florida’s Cape Canaveral Air Force Station. To show perspective, this spacecraft outlived the space shuttle program, which was in service from April 1981 to July 2011.
The daily activities of ISEE-3 can still be monitored through a Google project called “A Spacecraft for All.” At present time, the spacecraft is more than 430,000 miles from Earth (over 700,000 kilometers). In another 16 years, ISEE-3 will once again be on our cosmic doorstep as it approaches Earth again. Who knows, maybe it will be possible to once again raise a dormant spacecraft from “the dead.”