Microwaves Could Power Tomorrow’s Space Shuttles

By Carl Engelking | July 22, 2015 4:20 pm
A rendering of Escape Dynamics' microwave-powered space-plane. (Screengrab from YouTube/Escape Dynamics)

A rendering of Escape Dynamics’ microwave-powered space-plane. (Screen grab from YouTube/Escape Dynamics)

The same electromagnetic radiation used to heat up a Hot Pocket could propel a shuttle into space.

A Colorado-based technology company, Escape Dynamics, says initial testing indicates it’s possible to launch single-stage shuttles into orbit using microwaves beamed from the ground. If researchers can make the concept work, it could drastically reduce costs and make it safer to send satellites and humans into space.

Microwaves vs. Propellant

Currently, we rely on multistage rockets packed with an extraordinary amount of combustible fuel to propel shuttles into space. The fuel is heavy, making up about 90 percent of the rocket’s initial mass, which makes it expensive to ferry cargo and people into space — it costs anywhere from $5,000 to $50,000 per kilogram of payload delivered into orbit. Furthermore, there’s always a risk when you strap a human into a rocket that relies on powerful chemical combustion.

Escape Dynamics wants spacecraft to shed the weight and safety risks associated with explosive rocket fuel and use hydrogen for propellant. The space-plane would carry a far lighter fuel tank filled with hydrogen, which would be heated up by microwaves sent from Earth to the space-plane’s external microwave-absorbing heat exchanger. The hydrogen would heat up in the tank and eventually burst out of a nozzle system in the shuttle to create thrust.

When Escape Dynamics tested a scaled-down, ground-based thruster using helium as fuel, it generated a specific impulse — the force that moves a rocket through the air — of 500 seconds. Engineers believe they can push that number to 600 with hydrogen, a duration they believe would be enough to send their space-plane into space. For comparison, chemical combustion rockets top out at about 460 seconds.

If Escape Dynamics can perfect the technique, they believe their space-planes could fly into orbit, deliver a payload of about 200 to 400 pounds, glide back down to Earth and be reused multiple times — a goal Elon Musk’s SpaceX is currently pursuing.

Work to Do

There are still quite a few challenges standing in the way before Escape Dynamics’ microwave-powered space-plane can run missions to the International Space Station. Engineers need to make sure it’s possible to build a microwave antenna array powerful enough to push the craft into space. They also need to ensure the microwaves stay on target and, of course, that it’s safe to fire microwaves into space.

But if they can put all the pieces together, the system could radically transform the way we send people and cargo into space.

CATEGORIZED UNDER: Space & Physics
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  • Jim LeSire

    Great for nuking birds, too!

  • Jim LeSire

    I understand that hydrogen is very light, but it carries very little mass, and because of that produces less thrust than any other material. It’s a trade-off, but I think the subject should be explored thoroughly.

  • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

    far lighter fuel tank filled with hydrogen” The Space Scuttle’s LOX/H2 main engines generated 37 million horsepower or 27.6 gigawatts. You would need more than 10 Palo Verde, AZ nuclear power plants, more than 30 nuclear reactors red-lined, to microwave pull that off (counting conversion inefficiencies). What does a 28 gigawatt microwave horn look like, Yosemite National Park’s El Capitan?

    The fuel tank will require a rather large nominal volume.
    RP-1, 0.81 g/cm^3
    JP-10, 0.94 g/cm^3
    LOX, 1.141 g/cm^3
    Liquid hydrogen, 0.071 g/cm^3

  • Mike Richardson

    It’s an interesting concept in terms of simplifying the launch vehicle and saving on the weight of extra propellant. The only drawback is that the vehicle is dependent on the ground power source, although it looks like it could safely glide back to Earth in an emergency (based on the lifting body design shown). Well, the only other drawback might be as another poster put it, “nuking birds.” Unlike space to ground microwave transmission via solar power satellites, as envisioned by proponents of space-based solar energy, these beams would be tight and focused, meaning anything that crossed their path would not get a gentle warming effect, but instead receive lethal burns. So yes, anything that crossed that beam path would likely die, including our fine feathered friends. Be wary of any place selling fresh rotisserie chicken within a few miles of the launch site. 😉

    • Ivar Ivarson

      The number of fried birds would probably be quite small given how narrow the beam(s) used and how long they run. OTOH, the beams will likely track the launch vehicle covering more sky and thus more birds. Still probably only a fraction of a large glass sheathed building or a big windmill in terms of lethal area.

      • Mike Richardson

        Good point. And like busy airports, a spaceport could always take measures to deter birds from the flight paths of launching craft.

    • Van Snyder

      Space-based solar energy sounds like a keen idea, until you calculate how much energy is required to lift the power station to orbit. It can never produce enough energy, and beam it down, to repay that. It’s a net loss, and therefore a nutty idea, not a cool one.

      • Mike Richardson

        Only if you launch from Earth. Mine the moon or asteroids for the material to build the arrays (an idea going back to 1970s), and assemble outside of the Earth’s gravity well, and that isn’t a problem. But it does require some infrastructure in space for mining, refining, and assembling, so it’s probably at least a few decades away.

        • Van Snyder

          And how much energy will it take to establish a manufacturing infrastructure there? It’s still a nutty idea to try to justify on the basis of beaming down energy.

          • Mike Richardson

            No nuttier than an energy infrastructure based on burning a limited supply of polluting fossil fuels, and that’s been the business as usual model for the past century. We’ve spent trillions over the past several decades subsidizing the production and extraction of oil and coal. I’d wager it would cost less than that to invest in space-based power, and it would be better for us in the long run.

          • Van Snyder

            Show me the numbers that prove it’s not a net energy loss. Maybe after a space-based manufacturing infrastructure is established for entirely different reasons, it can start producing and exporting energy. By then, our climate will be screwed by what I believe we agree is a bad thing: burning fossil fuels. In the nearer term, perhaps before it’s too late, we can produce energy without CO2 emissions, and at the same time destroy nuclear waste, with a single system called the Integral Fast Reactor.

  • Sean M.

    This might be terribly naive of me, but what does it matter which gas you use? Hydrogen is lighter, but the thrust produced by an expanding gas is dependent on the mass of the gas, correct?

    • anna.dahl2
    • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

      Look up “specific impulse.” The lower the exhaust’s average molecular weight, the larger the specific impulse of a given mass of fuel. US H2/LOX rockets are run way over stoichiometry in hydrogen to boost I_sp (and film-cool rocket bell walls.)

      A rocket engine imparts momentum, (mass)(velocity). It requires energy to do it, (1/2)((mass)(velocity)^2. Faster exhaust doesn’t necessarily buy you more change in momentum/tankage unless the energy is cheap (or externally supplied).

  • threadnut

    This is interesting, jus in not having to lift the fuel.Great idea.

  • lharbaugh

    I remember this idea from a Jerry Pournelle novel from 30-40 years ago. He proposed using lasers rather than microwaves, but it was generally the same idea.

  • ericlipps

    300-400 pounds of payload sounds impressive, but it’s only about 2 to 3 people without food, water or air, or relatively small satellites. Modern communications satellites weigh tons.

    • http://careersreport.com Melissa Robi

      Let me show you how you can make some extra funds for doing basic jobs on computer few hrs weekly from your house>Visit my disqus profile for more info

  • Van Snyder

    The unit “seconds” of specific impulse is not a “duration.”

    A similar idea, using a laser to ablate lucite, was pondered by the McDonnell-Douglas Advanced Propulsion Division in Huntington Beach, CA, about 35 years ago. The size of lens/mirror/antenna to focus a laser to a given spot size at a given distance is significantly smaller than what would be needed for microwaves.

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