• Roge Velez Mendoza

The Unexpected Story of ISEE-3: Adventures of a Versatile Spacecraft

From studying solar winds and cosmic rays to hunting comets, the ISEE-3/ICE is a testimony to making things up as we go.

The versatile ISEE-3/ICE. Courtesy NASA.

In 1978, NASA and ESA launched a small spacecraft for a new—and somewhat specific—mission. Designed with a wide range of instruments (see below), the ISEE-3 (International Sun/Earth Explorer) was initially sent into orbit to monitor solar winds approaching Earth. Little did we know, the small craft would go on to map Earth's magnetic tail, hunt a couple of comets, orbit the Sun and, many years later, be the first spacecraft commanded by a non-governmental team in an interplanetary journey.

Just a Short, Simple Mission

ISEE-3 was launched on August 12, 1978, as the third of three Sun-Earths Explorers designed by the American and European space agencies. From the beginning, the 390 kilograms spacecraft was meant to be the first in many things. The satellite was the first to reach a stable halo orbit near a Lagrange point. This is cool for many reasons, but I'll mention three. First, a Lagrange or libration point is one of those only five places between two bodies (in this case, the Earth and the Sun) where you can park your car in neutral and expect to find it there months later. It's a relatively stable orbital sweet spot where the gravitational forces of both bodies cancel out—but in this case, the parking spot is 1.5 million kilometres from home. Second, we have known about these Lagrange points even before Italian mathematician Joseph-Louis Lagrange himself. It seems good-old-father-of-all-things Leonhard Euler deduced the existence of the first two around 1762, and Lagrange discovered the rest in 1772. And third, two centuries after calculating these points' position on paper, humans managed to put a highly functional satellite in one of those orbits.

The 390 kilograms spacecraft was meant to be the first in many things.

ISEE-3 was so good at its job that after three years, it was promoted from monitor of solar winds to surveyor of Earth's magnetic field. Engineers at the Goddard Space Flight Center fired the little guy's thrusters in June 1982 and moved it to the tail of our planet's Magnetosphere. Imagine the solar winds as a stream and the Earth as a small boat, tied in place by gravity. The magnetotail would be the wake and ripples left behind the planet. The spacecraft detected a huge plasmoid (a structure of plasma or electrified gas) ejected from the Earth's magnetosphere (similar to the one detected in Uranus last year). Kind of a giant magnetic bubble in the wake of the little boat.

Comet Hunting

Politics, of course, was not out of all the influences controlling ISEE-3's destiny. As the international competition for space exploration was still raging, several countries prepared to study Halley's Comet—the most famous "dirty snowball" we know—expected to arrive in 1986. With news of a Halley Armada of several comet-hunting spacecraft getting ready to launch, the U.S. did not lose the opportunity the grant ISEE-3 another "first." In 1982, NASA agreed to redirect the craft to rendezvous with another comet, named 21P/Giacobini-Zinner, and beat every other nation to the scoop on comet composition.

Courtesy NASA/Goddard Space Flight Center

So, now you can ask, what is a Sun-Earth Explorer doing going after a comet? Well, NASA probably saw the inconsistency as well and thought it was necessary to rename the spacecraft as the International Cometary Explorer (ICE). You know, to avoid such annoying questions. Well, our little renamed friend did exceptionally well and became the first spacecraft to fly past a comet when it got 7,800 kilometres from its nucleus in 1985. ICE passed through the comet's tail, sending never-before-seen data on the material that comets shed on their path. The decision to study Giacobini-Zinner, however, cost the ICE the opportunity to get closer to Halley's. While the most successful mission in the Armada, Giotto, made it as close as 596 km from the comet (roughly the driving distance between Montreal and New York City), and with other missions closing in on the thousands, ICE was only able to get a look from 40 million kilometres away.

So, now you can ask, what is a Sun-Earth Explorer doing going after a comet?

That was not the end of ISEE/ICE's missions, though. NASA parked it in orbit around the Sun, where it continued sending data until 1997. After that, the little spacecraft went into a siesta, travelling quietly and blindly, as if resting from two decades of hard work. For the American space agency, it had done its duty and more, and now it was time to retire it.

One Last Push

But hope came back to ISEE-3/ICE's story. Sixteen years after going to sleep, a team of scientists managed to raise US$159,000 from donations to wake up the sleeping spacecraft and bring it back to its original orbit with NASA's blessing. The ISEE-3 Reboot Project, composed of independent scientists and engineers, awakened and commanded the 36-year-old computer when it was closest to Earth in 2014. The spacecraft managed to fire its thrusters on July 2, but a more prolonged firing failed on July 8. Although the Reboot project failed its original mission to bring it back to Earth's orbit, it completed a space exploration milestone: it was the first time that a group of non-governmental scientists, funded by public donations, flew an interplanetary vessel.

ISEE-3, later renamed ICE, during a pre-launch inspection. Courtesy NASA/Goddard Space Flight Center

ISEE-3/ICE still meanders alone in the blackness of space, slowly revolving around the Sun. Its orbit now is less clear than ever before, and many people's hope is all but lost. Perhaps, around 2031, when the spacecraft is close to Earth once more, there may be something to be done for it. Or we could just let it be; let it keep wandering as it has before, in a well-deserved slumber.