It’s obvious, but I'll say it: Rockets are cool. Sending stuff into space with a chemical reaction is just stupid-awesome. But clearly, we can't keep using chemical rockets to put satellites in orbit. They're too expensive, and the fuel is heavy—which means you need even more fuel to carry the fuel.So I’m excited about this new proposed launch system, the SpinLaunch . The basic idea is to physically throw a missile off the planet, in much the same way our ancestors hurled rocks with a leather sling. In this case, a giant centrifuge would spin the craft around in a vacuum to build up insane speed, then open a door and release it into the sky.
Across the street a retro McDonnell Douglas sign perches above the aerospace giant’s former factory, and just around the corner Virgin Orbit is developing air-launched rockets .It’s a fitting headquarters for SpinLaunch, a company breathing new life into the decades-old idea of using giant mechanical slings to hurl rockets into orbit.
But the physicist in me also can’t help being a little skeptical. The challenges here—like air drag, for starters—seem enormous. I’m not saying this thing won’t work, but I want to crunch the numbers myself to see what’s involved. Come on, let's take it for a spin!Acceleration Sensation
Before I get to the calculations, let's look at the details of the system and the physics involved. Here's what I know about SpinLaunch from current specs:
- Launcher spins in a circle with a diameter of 100 meters.
- Payload mass of 100 kilograms, plus maybe another 100 kg for the spacecraft (I assume this is just a small prototype)
- Rotation speed at launch of 450 revolutions per minute
- Launch speed of 7,500 kilometers per hour (4,660 mph)
- Spin-up time of 1.5 hours
- Launch angle at 35 degrees
Just to be clear, it’s still a rocket. Once the craft reaches the outer atmosphere, at an altitude of about 60 kilometers, it uses a small rocket engine to push it the rest of the way.
Now for some physics. There's a bunch of stuff here, so I'll just go over the key ideas. I'll start with objects spinning in a circle. Suppose I take a ball on a string and swing it around in a horizontal plane. As viewed from the top, it would look like this: