This LEGO model fall into the "micromodel" category because some details were sacrificed to make it easier to build. The original spacecraft is formed by a 16-side cylinder, this model was made with 8-side cylinder. Another fine detail like thrusters, scientific instruments and antenna details were omitted due to the difficulty of being represented in the right size scale.
Each side side of the cylinder has two solar panels (upper and lower), antenna support and plate brick. The top and bottom pieces of the cylinder are made of 4x4 round plates.
The inside of the spacecraft is made of a superposed crosses structure, this is one of the techniques used to build cylindrical objects. The colors of the insider bricks are irrelevant because aren't viewed from the exterior.
In the center of the cross lies a "fire hydrant " brick with 6 connecting points. The arms of the crosses could be made with any kind (or combination) of 1x1 bricks with the same length shown.
The building process takes around 150 steps. In the finished model the biggest characteristics of ISEE-3 are long and symmetrical antennas, instrument masts and blue solar panels