later years of "Classic" Space, but redesigned its minifigures. They came in four colors (red, blue, yellow, and black) but had a new design with a zipper crossing from hip to shoulder and the color on top with white below, as well as using a newly redesigned helmet with a transparent blue visor. Instead of a large spaceship, the theme centered around the Monorail Transport System, which featured a battery-powered train and some twenty linear feet of track. At the time, this was the most expensive Lego set. Blacktron (1987–1988) Along with Futuron, Blacktron was one of the first unified sub-themes in Space. The set designs were based around a black and yellow color scheme with transparent yellow windscreens and transparent red highlights. Blacktron minifigures wore black jumpsuits akin to today's military pilots, with white trim and opaque black visors. Blacktron was a major step forward in set design from the rather clunky "Classic" Space designs. It featured a large spacecraft, the "Renegade", which set the tone for all future big ships by splitting into a number of smaller modules, including a storage bin for a small, wheeled vehicle, that could be recombined not just with each other but with modules from other vehicles in the theme, specifically the "Invader" and "Battrax". This modular interchangeability became a staple of Lego Space until 2001. Space Police (1989) In 1989, Lego decided to further its storyline direction with the introduction of Space Police to oppose Blacktron, since police and robbers were popular sellers in its Lego Town theme. The Space Police sets had a black, blue, with red transparent color scheme, and the minifigures shared the torso design with the black Futuron minifigure, but with a transparent red visor. This would be the first time that Lego had a "bad guy", "good guy" and "civilian" faction, a theme that would be used for the next decade. Space Police also used modular systems but on a smaller scale by featuring a Space Police jail cell that could be used interchangeably among almost all sets and came with a Blacktron occupant. M:Tron (1990–1991) In 1990, Lego designed its next theme around magnets. After the introduction of Space Police, M:Tron was introduced as a repair and rescue faction, the space equivalent of a fire brigade. However, for the American market, the faction was depicted as a mining and exploration faction, adapting the names of the