That's what the little squares nailed to the outside of the hull appear to be, and I don't see an external mast to hang a nuke, or radiators to carry off the waste heat.

ISEE-3 originally operated in a halo orbit about the L1 Sun-Earth Lagrangian point, 235 Earth radii above the surface (about 1.5 million km, or 924,000 miles). It was the first artificial object placed at a so-called "libration point", proving that such a suspension between gravitational fields was possible. It rotates at 20 rpm about an axis perpendicular to the ecliptic, to keep it oriented for its experiments, to generate solar power and to communicate with Earth.

http://en.wikipedia.org/wiki/International_Cometary_Explorer

It appears to have run out of compressed N2 to force fuel and oxidizer to the engines.

On May 29, 2014, two-way communication with the spacecraft was reestablished by the ISEE-3 Reboot Project, an unofficial group[4] with support from the Skycorp company.[5][6][7] On July 2, 2014, they successfully fired the thrusters for the first time since 1987. However, later firings of the thrusters, on July 8, 2014, failed, apparently due to a depleted supply of nitrogen, essential in pushing the hydrazine fuel to the thrusters. According to the project team, an alternative plan in the use of the spacecraft is to "collect scientific data and send it back to Earth."[8]

Too bad, recycling these old birds and giving them new missions they weren't even originally designed for is engineering at its finest.