Rocket boots are one of those things that comes up again and again in science fiction because the fundamental idea is so basic and desirable. More stylish than a jetpack, too. Iron Man loves them, as does the Star-Lord from Guardians of the Galaxy. I just never thought they could work, until I talked to Dr. Larry Silverberg at NC State.
In fact, here's a direct quote from the good doctor on the feasibility of rocket boots:
No question it's possible.
That's a pretty solid endorsement.
Dr. Silverberg's core research areas include aerodynamics, propulsion, space exploration systems, energy systems, structural mechanics, dynamics, vibrations, controls — he's one of the best possible people I could ask about rocket boots, really.
I came into this expecting Dr.Silverberg to dismiss them out of hand. I was so sure that I came in with the caveat that we didn't even have to deal with the huge engineering issues of rocket boots, such as adequate fuel storage and all that. If we just accept that the technology is feasible, would these boots even be remotely controllable?
In my head I was picturing how I would be with a pair of rockets firing down from my heels. I imagine it would be a few seconds of hovering elation, followed by minutes of me saying OW OW OW OW FOR THE LOVE OF GOD GET THEM OFF ME as I was repeatedly slammed into buildings and pavement by a pair of wildly gyrating rockets attached to my feet, flinging me around like a ragdoll on fire.
But Dr.Silverberg brought up one thing I hadn't considered: the Segway.
See, this dorkiest-looking of personal transportation technology also has the seeds in it for possibly the coolest-looking personal transportation technology. They key is in the same technology that the Segway uses to remain upright on its two wheels. That same system of gyros, sensors, feedback and motors could be employed to make rocket boots work like they do in fiction and not in my insecure self-destructive fantasies.
Essentially, the rocket boots would behave in the same way your hand does when you balance a broom vertically — it shifts and moves with the broom to keep the center of gravity where you want it. Viable rocket boots would need to have vectored thrust, via a gimbaled exhaust nozzle or some other (vanes, etc) method. You can't just thrust straight down from the heels; you need to adjust, continuously, the direction of the thrust.
As far as your body's ability to withstand the force, your legs are actually capable of withstanding about 1000 lbs of force when you jump, according to Dr. Silverberg. The human body should be able to endure most rocket boot thrust. The weak point would be the knees, so, ideally, rocket boots would be thigh-highs, with the thrust coming from about halfway between the knee and foot.
Dr. Silverberg speculated that something with two rockets on the front of the boot and two on the rear would probably work well. The knee joint could be locked as needed to prevent buckling or injury, and to make controlling the flight path more manageable.
In fact, the biggest limitation a person in rocket boots would face would be blacking out from high G force loads, so if you're trying this on your own, best to keep the speeds fairly low.
Since Dr.Silverberg pretty effectively convinced me that a dynamically-vectored thrust system using a Segway-like CoG management computer system could make rocket boots controllable, I pressed on to see if they could be plausible even if we now were forced to deal with real-world engineering. No assumptions of magical fuel and energy sources.
In that case, Dr.Silverberg still feels they're possible, but you're not going to fly with them. At best, you'll get one really good 20-story jump from them. The problem with them is, like jetpacks, fuel. You simply can't cram enough fuel in a pair of boots — even massive platform boots — to get enough energy to fly more than a few seconds.
So, if you wanted a one-shot leaping superpower, hell yes, get yourself some rocket boots. If you want to take off and leisurely fly around the city and hover in front of bathroom windows on high-rise apartments, I'm afraid you're out of luck.
We also discussed the possibility of rocket boots with an electrically-powered plasma motor taking power from the electrical grid via long, trailing wires, then the idea came up of how it'd be nice to at least have a seat while you were flying around, then we got into weather protection, and before you knew it we re-invented the ski lift.
Sometimes its best to quit while you're ahead.
Still, the big take-away here is that yes, rocket boots are possible. Even with all the real-world caveats, you've still got a pair of boots that could let you jump onto the roof of a skyscraper, and that's pretty damn cool.
Looks like I owe Iron Man an apology. Fruit basket?