If you're going to 3D-print rocket parts, you'd want to make them out of metal to handle the stress, right? Not necessarily. MIT has successfully test-fired what it believes is the first completely 3D-printed rocket motor to be made with plastic casing. That's right -- an all too easily melted material was sitting a virtual hair's breadth away from super-hot propellant. It sounds like a recipe for disaster, but apparently it worked well -- it generated real thrust, and there was only a small amount of damage to the motor's throat after the initial run. A second test didn't fare so well (it would be useless for moving anything), but MIT hadn't intended for the motor to fire more than once.
This wasn't just a because-we-can experiment. Metal 3D printing is expensive (the printers alone cost hundreds of thousands of dollars). MIT's printer, a Markforged Mark Two, costs "just" $13,499. That's not exactly an impulse purchase, but it could give small teams a chance at building rockets that would otherwise be impossible with a relatively modest budget. And while it's not stated, it's easy to see larger space agencies using this to keep costs down, especially for rockets that are unlikely to be used more than once or for long durations.
There's a lot to accomplish before that happens. The scientists are researching larger, more resilient motors. Eventually, they're aiming for plastic-hulled rockets powerful enough for flight. Don't be surprised if you one day see lighter, cheaper rockets that only use metal sparingly.