Not Coming Soon to a Spaceship Near You

Mustafa’s Space Drive: An Egyptian Student’s Quantum Physics Invention

Mustafa invented a way of tapping this quantum effect via what’s known as the dynamic Casimir effect. This uses a “moving mirror” cavity, where two very reflective very flat plates are held close together, and then moved slightly to interact with the quantum particle sea. It’s horribly technical, but the end result is that Mustafa’s use of shaped silicon plates similar to those used in solar power cells results in a net force being delivered. A force, of course, means a push or a pull and in space this equates to a drive or engine.

In terms of space propulsion, this is amazing. Most forms of spacecraft rely on the rocket principle to work: Some fuel is made energetic and then thrust out of an engine, pushing the rocket forward.

First of all: clever. The dynamic Casimir force was observed last year or thereabouts (thenabouts?), and it breaks down like this: the vacuum isn’t empty, it has a bunch of virtual photons and other virtual particle/antiparticle pairs in it. In the static Casimir effect you can get a force by excluding some of the EM modes, which gives an imbalance in the energy, which manifests itself as a force. In the dynamic Casimir effect, you move a mirror really fast and create real photons from the virtual photons (basically you are adding energy to them to allow them to become real). So as far as I can tell, this drive is photons. The generation of the photons is a new process, but at the end of the day, it’s photons. From a dynamics standpoint, this is going to be the same as shining an LED out of your rocket and feeling the thrust, because photons have momentum. This is the rocket principle, despite the implication of the article.

Which means this all boils down to how efficiently you can make your photons, from an energy and thrust/weight standpoint. I suspect that energy-wise, this is an inefficient way of making photons; LEDs are in the vicinity of 50% in converting input power to photons. All of that presupposes that photons are a good solution to the space propulsion problem, but photons are very inefficient in terms of how much momentum you get for the energy you use.

For a photon, the momentum is simply E/c. 1 eV of photons (be is a single photon or a bunch of lower-energy ones, it doesn’t matter) gives you a momentum of about 5 x 10^-28 kg-m/s of momentum. (Non-relativistic) Massive particles, though, have a momentum of sqrt(2mE). Give that same energy to a hydrogen atom and you get almost 50,000 times as much momentum; this scales with the square root of the mass, so Xenon, with an atomic mass ~130 times larger, boosts your momentum by another factor of 11 or so. That’s what you get with ion drives, and those still have limited use.

And Mustafa’s invention can, rudimentarily, be compared to a solar sail…because it doesn’t need “fuel” as such, and exerts just the tiniest push compared to the thundery flames of SpaceX’s rockets. It’s potential is enormous–because of its mechanical simplicity and reliability it could make satellite propulsion lighter, cheaper, and thus indirectly lower the cost of space missions of all sorts.

It’s actually half as efficient as a solar sail, because a reflection gives you twice the change in momentum (since the photon changes direction) and while, like an LED, no fuel is needed, you still need the energy source to run the thing. So it remains to be seen if this is viable and better than existing systems, but there’s a reason why we don’t use photons already (other than by accident, as with the mentioned Pioneer anomaly — which was a ten billionth of a g, i.e. a tiny effect) and this isn’t going to get you into orbit in the first place.

6 thoughts on “Not Coming Soon to a Spaceship Near You

  1. Scale down expectations, for the mass/area of silicon required is not particularly reflective or conductive to create the Casimir etalon, ditto graphene. One would obtain immensely more thrust by pissing into vacuum (thereby circumventing the “wind” boundary condition, obviously in a way not obvious to one skilled in the art, and therefore patentable).

    But wait! If we set up deep ultrasonic organ pipe resonance in a plasma column, say at THz frequencies, the compressions and rarefactions would mimic a vibrating jellium surface! We could then apply for DARPA funding citing extrapolation to 10^44 J GRB rigs (giant resonance bells, not gamma ray bursts or grant recovery bountyhunting).

  2. When you look at efficiency in terms of energy, you’re looking at the wrong thing. There’s a sort of paradox with rocket propulsion. With a chemical rocket, you want your fuel to have a high specific impulse, which is the change in momentum per unit mass. This equates to having the highest possible propellant velocity, which also means you’re actually using the highest kinetic energy.

    So an “efficient” rocket in terms of momentum/mass is very inefficient in terms of momentum/energy. I’m not sure if this same principle holds for an engine that uses the Casimir force.

  3. You already got the “EM radiation is a terrible way to get momentum” angle, but here’s my other issue–if you heart is set on sending out EM radiation for the impulse, just use a high efficiency antenna (you can get 90% energy conversion efficiency, and then just put it in a parabolic mirror) or a laser (easier to focus, solid state gives you about 50% efficiency). Currently the Dynamic Casimir gives efficiencies like 10^-16 or so (the effect is relativistic, with number of photons generated ~ (v/c)^2). You can use SQUIDs to get “high” v/c (10^-7 so far) and high Q cavities to improve this number, but why bother when you can already generate photons so efficiently?

  4. And then I re-read your post and you mention using LEDs, so you covered that angle already. Whoops, I feel silly.

  5. I am going to try this post again. I am actually surprised that something similar based on the Casimir effect hasn’t been patented already. I am curious about the quality and spectrum of the photons produced and the type of vibrations that are needed to generate photons in setup. One could imagine one application of dynamic Casimir technology would be in some type of stability sensor or motion sensor, where photons off specific frequency would be generated in response to motion such that they could be identified readily in a detector. It would have one advantage in that it would operate best in a vacuum

Comments are closed.