The Space Defense Front are a terrorist organization featured in the Planetes anime. They are mainly seen in the later episodes.
The Space Defense Front are angered over humanity's rapid expansion into space without dealing with the social, economic and ecological issues on Earth. They believe that space expansion is a way for rich countries to get richer and leave developing nations stranded in poverty.
At first, they try to trigger Kessler Syndrome by destroying the Technora orbital station, creating enough space debris to stop all space flights for hundreds of years. After this is stopped by Fee Carmichael, they shift towards trying to drop the Von Braun spaceship onto the Moon.