In the — pleasant — 1970s film “Silent Running”, it has been decided that the space ship will “return to commercial service”. But why blow up the Domes? The workers are in a hurry, and this operation costs explosive nuclear tanks.
There was never a direct answer given in the movie or in the book. However, there are a few factors:
- The domes required maintenance. While they apparently had a large area in each dome, it wasn't enough for an entire ecosystem. This is shown by Lowell's need to take care of them and his leaving one drone behind to take care of the forest. So leaving the domes out there, alone, would likely not preserve the habitats well. There would be no gain from leaving them out there.
- We're beginning to find out, now, in dealing with just what's in orbit around Earth, that space debris can be troublesome and even dangerous. The domes did not appear to have any ability to change course on their own (other than simple thrusters to detach from the ships), so their orbits would not be stable and they would soon become navigation hazards.
Beyond that, there's really no solid reason, but #2 can be a serious issue.
I loved the movie as a teen, but was only able to see it once or twice, but I read the book many, many times. The school librarian finally gave it to me because I checked it out so often and nobody else read it. But at one point the story for it all just fell apart for me for too many reasons:
- There are too many people that enjoy nature to make it believable that Earth, as a whole, would just give up on nature so easily.
- The ships were orbiting out near Saturn, which would mean there would be too little light in the first place, not just after the Valley Forge continued off course.
- There's no real reason or need to put ships THAT far from the sun, especially when the plants on them need sunlight.
There's more, but it helps to remember the background of the movie. It was made by Douglas Trumbull, after making 2001: A Space Odyssey. There was a big discussion during the movie about whether they could make a convincing Saturn, and that it took more work to do Saturn than Jupiter (both required the planet, but Saturn needed rings, too). Some say Trumbull's entire purpose behind the movie was to prove he could make a good Saturn. Others say that the shots of Saturn were originally intended for 2001.
The movie was made on a budget of $1 million, had a 1:1 shooting ratio (almost impossible to do - it means no outtakes at all) and the original story was not environmentally focused. There were major changes in the storyline (I've never been clear why - probably due to budgeting), so the lack of logic is likely a result of pressured re-writing to either meet deadlines or an unbelievably low budget, even for then.
Based on the film's official novelisation, the answer appears to be that the domes (with their cargo of plants and animals) represent a clear and present threat to the safety of Earth. There are mentions of the planet having achieved some sort of stable global temperature and cured pretty much every disease. People are being fed and the population is growing rather than declining.
Returning the domes to Earth (or even having them in orbit) could easily lead to the reintroduction of diseases that have since been eradicated and could threaten the status-quo in terms of food production. Blowing them up prevents any potential for this to happen.
He lifted some of the food from Keenan’s plate. “Look at that. Fried synthetic glop! And you’ve become so dependent on it that I’ll bet you can’t even live without it.”
“I don’t even want to, Lowell,” Barker muttered.
Lowell stared incredulously. “Do you realize how pitiful that is, what you just answered? On Earth everywhere you go the temperature is seventy-five degrees. Everything’s the same. All the people are exactly the same.”
He paused and asked in a hushed voice, “And what kind of life is that?”
“Lowell, if it’s so rotten, why do you want to go back?” Barker demanded.
“Because it’s not too late to change it.”
Keenan with a half laugh leaned forward.
“What do you want, Lowell? There’s hardly any more disease. There’s no more poverty. Nobody’s out of a job.”
Although there's a tendency for us, the viewer to idolise the natural world depicted inside the domes, the reality is that in the film most people on Earth have long stopped caring about seeing a real tree and would prefer to get on with their (well-fed, disease-free, no-poverty) lives without having to worry about some lunatic eco-warrior deciding that it would be great idea to reintroduce the plague flea or cover the world in stinging nettles.