Symbolism, Imagery, Allegory
Rockets are all over this book, from the first story (when a rocket changes the weather), to the last (when a rocket is used to change history). Some critics think Bradbury is anti-technology, and they might have a point: as the dad says in "The Million-Year Picnic," "the people got lost in a mechanical wilderness, like children making over pretty things, gadgets, helicopters, rockets; emphasizing the wrong items, emphasizing machines instead of how to run the machines" (123).
Rockets don't come off any better in "The Locusts," when they land on Mars and "set the bony meadows afire, turned rock to lava, turned wood to charcoal, transmitted water to steam, made sand and silica into green glass which lay like shattered mirrors reflecting the invasion, all about" (1).
Or check out what they do in "The Naming of Names": "And the rockets struck at the names like hammers, breaking away the marble into shale, shattering the crockery milestones that named the old towns, in the rubble of which great pylons were plunged with new names: IRON TOWN, STEEL TOWN, ALUMINUM CITY, ELECTRIC VILLAGE, CORN TOWN, GRAIN VILLA, DETROIT II, all the mechanical names and the metal names from Earth" (2).
Okay, Bradbury: we get it. Rockets are bad.
But are they, really? After all, Bradbury seems to like the idea of people exploring and finding out new things and being curious about the world around them. And rockets do that. They can also save the world, like the family that they bring to Mars in "The Million-Year Picnic." (Although arguably the family wouldn't have needed saving if it weren't for technology in the first place.)
Well, take a look at the very first time we see rockets, in "Rocket Summer." When we first see a rocket, it's standing "in the cold winter morning, making summer with every breath of its mighty exhausts" (5).
That sounds pretty neutral, actually. When we start the book, rockets aren't good or bad. They just are. It's up to people to make them into symbols either of positive change—hope, exploration, new starts; or negative destruction.
Unfortunately, you know which one they choose.