A heatsink works because there is some sort of medium that absorbs heat from the sink and moves away, thereby moving heat away. On earth, we use air for this, sometimes with the help of a fan.
If you stick a heatsink on equipment in space, there's no air that can move the heat away, since space is mostly empty. You'll bleed off some through infrared radiation, but that's not going to be enough.
If you stick a heatsink on equipment in space, there's no air that can move the heat away, since space is mostly empty. You'll bleed off some through infrared radiation, but that's not going to be enough.